Auto merge of #122338 - workingjubilee:rollup-xzpt4v4, r=workingjubilee

Rollup of 15 pull requests

Successful merges:

 - #116791 (Allow codegen backends to opt-out of parallel codegen)
 - #116793 (Allow targets to override default codegen backend)
 - #117458 (LLVM Bitcode Linker: A self contained linker for nvptx and other targets)
 - #119385 (Fix type resolution of associated const equality bounds (take 2))
 - #121438 (std support for wasm32 panic=unwind)
 - #121893 (Add tests (and a bit of cleanup) for interior mut handling in promotion and const-checking)
 - #122080 (Clarity improvements to `DropTree`)
 - #122152 (Improve diagnostics for parenthesized type arguments)
 - #122166 (Remove the unused `field_remapping` field from `TypeLowering`)
 - #122249 (interpret: do not call machine read hooks during validation)
 - #122299 (Store backtrace for `must_produce_diag`)
 - #122318 (Revision-related tweaks for next-solver tests)
 - #122320 (Use ptradd for vtable indexing)
 - #122328 (unix_sigpipe: Replace `inherit` with `sig_dfl` in syntax tests)
 - #122330 (bootstrap readme: fix, improve, update)

r? `@ghost`
`@rustbot` modify labels: rollup

Cargo.lock

@@ -2265,6 +2265,17 @@ checksum = "f9d642685b028806386b2b6e75685faadd3eb65a85fff7df711ce18446a422da"
 name = "lld-wrapper"
 version = "0.1.0"
 
+[[package]]
+name = "llvm-bitcode-linker"
+version = "0.0.1"
+dependencies = [
+ "anyhow",
+ "clap",
+ "thiserror",
+ "tracing",
+ "tracing-subscriber",
+]
+
 [[package]]
 name = "lock_api"
 version = "0.4.11"

Cargo.toml

@@ -34,6 +34,7 @@ members = [
   "src/tools/expand-yaml-anchors",
   "src/tools/jsondocck",
   "src/tools/jsondoclint",
+  "src/tools/llvm-bitcode-linker",
   "src/tools/html-checker",
   "src/tools/bump-stage0",
   "src/tools/replace-version-placeholder",

compiler/rustc_codegen_llvm/src/context.rs

@@ -77,8 +77,8 @@ pub struct CodegenCx<'ll, 'tcx> {
     /// See <https://llvm.org/docs/LangRef.html#the-llvm-compiler-used-global-variable> for details
     pub compiler_used_statics: RefCell<Vec<&'ll Value>>,
 
-    /// Mapping of non-scalar types to llvm types and field remapping if needed.
-    pub type_lowering: RefCell<FxHashMap<(Ty<'tcx>, Option<VariantIdx>), TypeLowering<'ll>>>,
+    /// Mapping of non-scalar types to llvm types.
+    pub type_lowering: RefCell<FxHashMap<(Ty<'tcx>, Option<VariantIdx>), &'ll Type>>,
 
     /// Mapping of scalar types to llvm types.
     pub scalar_lltypes: RefCell<FxHashMap<Ty<'tcx>, &'ll Type>>,
@@ -105,15 +105,6 @@ pub struct CodegenCx<'ll, 'tcx> {
     pub renamed_statics: RefCell<FxHashMap<DefId, &'ll Value>>,
 }
 
-pub struct TypeLowering<'ll> {
-    /// Associated LLVM type
-    pub lltype: &'ll Type,
-
-    /// If padding is used the slice maps fields from source order
-    /// to llvm order.
-    pub field_remapping: Option<SmallVec<[u32; 4]>>,
-}
-
 fn to_llvm_tls_model(tls_model: TlsModel) -> llvm::ThreadLocalMode {
     match tls_model {
         TlsModel::GeneralDynamic => llvm::ThreadLocalMode::GeneralDynamic,

compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -5,6 +5,7 @@ use crate::errors::{
 };
 use crate::llvm;
 use libc::c_int;
+use rustc_codegen_ssa::base::wants_wasm_eh;
 use rustc_codegen_ssa::traits::PrintBackendInfo;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::small_c_str::SmallCStr;
@@ -98,6 +99,10 @@ unsafe fn configure_llvm(sess: &Session) {
             }
         }
 
+        if wants_wasm_eh(sess) {
+            add("-wasm-enable-eh", false);
+        }
+
         if sess.target.os == "emscripten" && sess.panic_strategy() == PanicStrategy::Unwind {
             add("-enable-emscripten-cxx-exceptions", false);
         }
@@ -523,6 +528,10 @@ pub(crate) fn global_llvm_features(sess: &Session, diagnostics: bool) -> Vec<Str
             .map(String::from),
     );
 
+    if wants_wasm_eh(sess) && sess.panic_strategy() == PanicStrategy::Unwind {
+        features.push("+exception-handling".into());
+    }
+
     // -Ctarget-features
     let supported_features = sess.target.supported_target_features();
     let mut featsmap = FxHashMap::default();

compiler/rustc_codegen_llvm/src/type_of.rs

@@ -1,5 +1,4 @@
 use crate::common::*;
-use crate::context::TypeLowering;
 use crate::type_::Type;
 use rustc_codegen_ssa::traits::*;
 use rustc_middle::bug;
@@ -10,7 +9,6 @@ use rustc_target::abi::HasDataLayout;
 use rustc_target::abi::{Abi, Align, FieldsShape};
 use rustc_target::abi::{Int, Pointer, F128, F16, F32, F64};
 use rustc_target::abi::{Scalar, Size, Variants};
-use smallvec::{smallvec, SmallVec};
 
 use std::fmt::Write;
 
@@ -18,7 +16,6 @@ fn uncached_llvm_type<'a, 'tcx>(
     cx: &CodegenCx<'a, 'tcx>,
     layout: TyAndLayout<'tcx>,
     defer: &mut Option<(&'a Type, TyAndLayout<'tcx>)>,
-    field_remapping: &mut Option<SmallVec<[u32; 4]>>,
 ) -> &'a Type {
     match layout.abi {
         Abi::Scalar(_) => bug!("handled elsewhere"),
@@ -71,8 +68,7 @@ fn uncached_llvm_type<'a, 'tcx>(
         FieldsShape::Array { count, .. } => cx.type_array(layout.field(cx, 0).llvm_type(cx), count),
         FieldsShape::Arbitrary { .. } => match name {
             None => {
-                let (llfields, packed, new_field_remapping) = struct_llfields(cx, layout);
-                *field_remapping = new_field_remapping;
+                let (llfields, packed) = struct_llfields(cx, layout);
                 cx.type_struct(&llfields, packed)
             }
             Some(ref name) => {
@@ -87,7 +83,7 @@ fn uncached_llvm_type<'a, 'tcx>(
 fn struct_llfields<'a, 'tcx>(
     cx: &CodegenCx<'a, 'tcx>,
     layout: TyAndLayout<'tcx>,
-) -> (Vec<&'a Type>, bool, Option<SmallVec<[u32; 4]>>) {
+) -> (Vec<&'a Type>, bool) {
     debug!("struct_llfields: {:#?}", layout);
     let field_count = layout.fields.count();
 
@@ -95,7 +91,6 @@ fn struct_llfields<'a, 'tcx>(
     let mut offset = Size::ZERO;
     let mut prev_effective_align = layout.align.abi;
     let mut result: Vec<_> = Vec::with_capacity(1 + field_count * 2);
-    let mut field_remapping = smallvec![0; field_count];
     for i in layout.fields.index_by_increasing_offset() {
         let target_offset = layout.fields.offset(i as usize);
         let field = layout.field(cx, i);
@@ -120,12 +115,10 @@ fn struct_llfields<'a, 'tcx>(
             result.push(cx.type_padding_filler(padding, padding_align));
             debug!("    padding before: {:?}", padding);
         }
-        field_remapping[i] = result.len() as u32;
         result.push(field.llvm_type(cx));
         offset = target_offset + field.size;
         prev_effective_align = effective_field_align;
     }
-    let padding_used = result.len() > field_count;
     if layout.is_sized() && field_count > 0 {
         if offset > layout.size {
             bug!("layout: {:#?} stride: {:?} offset: {:?}", layout, layout.size, offset);
@@ -143,8 +136,7 @@ fn struct_llfields<'a, 'tcx>(
     } else {
         debug!("struct_llfields: offset: {:?} stride: {:?}", offset, layout.size);
     }
-    let field_remapping = padding_used.then_some(field_remapping);
-    (result, packed, field_remapping)
+    (result, packed)
 }
 
 impl<'a, 'tcx> CodegenCx<'a, 'tcx> {
@@ -224,7 +216,7 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyAndLayout<'tcx> {
             _ => None,
         };
         if let Some(llty) = cx.type_lowering.borrow().get(&(self.ty, variant_index)) {
-            return llty.lltype;
+            return llty;
         }
 
         debug!("llvm_type({:#?})", self);
@@ -236,7 +228,6 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyAndLayout<'tcx> {
         let normal_ty = cx.tcx.erase_regions(self.ty);
 
         let mut defer = None;
-        let mut field_remapping = None;
         let llty = if self.ty != normal_ty {
             let mut layout = cx.layout_of(normal_ty);
             if let Some(v) = variant_index {
@@ -244,22 +235,15 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyAndLayout<'tcx> {
             }
             layout.llvm_type(cx)
         } else {
-            uncached_llvm_type(cx, *self, &mut defer, &mut field_remapping)
+            uncached_llvm_type(cx, *self, &mut defer)
         };
         debug!("--> mapped {:#?} to llty={:?}", self, llty);
 
-        cx.type_lowering
-            .borrow_mut()
-            .insert((self.ty, variant_index), TypeLowering { lltype: llty, field_remapping });
+        cx.type_lowering.borrow_mut().insert((self.ty, variant_index), llty);
 
         if let Some((llty, layout)) = defer {
-            let (llfields, packed, new_field_remapping) = struct_llfields(cx, layout);
+            let (llfields, packed) = struct_llfields(cx, layout);
             cx.set_struct_body(llty, &llfields, packed);
-            cx.type_lowering
-                .borrow_mut()
-                .get_mut(&(self.ty, variant_index))
-                .unwrap()
-                .field_remapping = new_field_remapping;
         }
         llty
     }

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -24,6 +24,7 @@ use rustc_span::symbol::Symbol;
 use rustc_target::spec::crt_objects::CrtObjects;
 use rustc_target::spec::LinkSelfContainedComponents;
 use rustc_target::spec::LinkSelfContainedDefault;
+use rustc_target::spec::LinkerFlavorCli;
 use rustc_target::spec::{Cc, LinkOutputKind, LinkerFlavor, Lld, PanicStrategy};
 use rustc_target::spec::{RelocModel, RelroLevel, SanitizerSet, SplitDebuginfo};
 
@@ -1350,6 +1351,7 @@ pub fn linker_and_flavor(sess: &Session) -> (PathBuf, LinkerFlavor) {
                         }
                     }
                     LinkerFlavor::Bpf => "bpf-linker",
+                    LinkerFlavor::Llbc => "llvm-bitcode-linker",
                     LinkerFlavor::Ptx => "rust-ptx-linker",
                 }),
                 flavor,
@@ -1367,8 +1369,17 @@ pub fn linker_and_flavor(sess: &Session) -> (PathBuf, LinkerFlavor) {
 
     // linker and linker flavor specified via command line have precedence over what the target
     // specification specifies
-    let linker_flavor =
-        sess.opts.cg.linker_flavor.map(|flavor| sess.target.linker_flavor.with_cli_hints(flavor));
+    let linker_flavor = match sess.opts.cg.linker_flavor {
+        // The linker flavors that are non-target specific can be directly translated to LinkerFlavor
+        Some(LinkerFlavorCli::Llbc) => Some(LinkerFlavor::Llbc),
+        Some(LinkerFlavorCli::Ptx) => Some(LinkerFlavor::Ptx),
+        // The linker flavors that corresponds to targets needs logic that keeps the base LinkerFlavor
+        _ => sess
+            .opts
+            .cg
+            .linker_flavor
+            .map(|flavor| sess.target.linker_flavor.with_cli_hints(flavor)),
+    };
     if let Some(ret) = infer_from(sess, sess.opts.cg.linker.clone(), linker_flavor) {
         return ret;
     }
@@ -2338,8 +2349,12 @@ fn add_order_independent_options(
         });
     }
 
-    if flavor == LinkerFlavor::Ptx {
-        // Provide the linker with fallback to internal `target-cpu`.
+    if flavor == LinkerFlavor::Llbc {
+        cmd.arg("--target");
+        cmd.arg(sess.target.llvm_target.as_ref());
+        cmd.arg("--target-cpu");
+        cmd.arg(&codegen_results.crate_info.target_cpu);
+    } else if flavor == LinkerFlavor::Ptx {
         cmd.arg("--fallback-arch");
         cmd.arg(&codegen_results.crate_info.target_cpu);
     } else if flavor == LinkerFlavor::Bpf {

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -153,6 +153,7 @@ pub fn get_linker<'a>(
         LinkerFlavor::Msvc(..) => Box::new(MsvcLinker { cmd, sess }) as Box<dyn Linker>,
         LinkerFlavor::EmCc => Box::new(EmLinker { cmd, sess }) as Box<dyn Linker>,
         LinkerFlavor::Bpf => Box::new(BpfLinker { cmd, sess }) as Box<dyn Linker>,
+        LinkerFlavor::Llbc => Box::new(LlbcLinker { cmd, sess }) as Box<dyn Linker>,
         LinkerFlavor::Ptx => Box::new(PtxLinker { cmd, sess }) as Box<dyn Linker>,
     }
 }
@@ -1824,7 +1825,7 @@ impl<'a> Linker for PtxLinker<'a> {
             }
 
             Lto::No => {}
-        };
+        }
     }
 
     fn output_filename(&mut self, path: &Path) {
@@ -1862,6 +1863,104 @@ impl<'a> Linker for PtxLinker<'a> {
     fn linker_plugin_lto(&mut self) {}
 }
 
+/// The `self-contained` LLVM bitcode linker
+pub struct LlbcLinker<'a> {
+    cmd: Command,
+    sess: &'a Session,
+}
+
+impl<'a> Linker for LlbcLinker<'a> {
+    fn cmd(&mut self) -> &mut Command {
+        &mut self.cmd
+    }
+
+    fn set_output_kind(&mut self, _output_kind: LinkOutputKind, _out_filename: &Path) {}
+
+    fn link_dylib_by_name(&mut self, _name: &str, _verbatim: bool, _as_needed: bool) {
+        panic!("external dylibs not supported")
+    }
+
+    fn link_staticlib_by_name(
+        &mut self,
+        _name: &str,
+        _verbatim: bool,
+        _whole_archive: bool,
+        _search_paths: &SearchPaths,
+    ) {
+        panic!("staticlibs not supported")
+    }
+
+    fn link_staticlib_by_path(&mut self, path: &Path, _whole_archive: bool) {
+        self.cmd.arg(path);
+    }
+
+    fn include_path(&mut self, path: &Path) {
+        self.cmd.arg("-L").arg(path);
+    }
+
+    fn debuginfo(&mut self, _strip: Strip, _: &[PathBuf]) {
+        self.cmd.arg("--debug");
+    }
+
+    fn add_object(&mut self, path: &Path) {
+        self.cmd.arg(path);
+    }
+
+    fn optimize(&mut self) {
+        match self.sess.opts.optimize {
+            OptLevel::No => "-O0",
+            OptLevel::Less => "-O1",
+            OptLevel::Default => "-O2",
+            OptLevel::Aggressive => "-O3",
+            OptLevel::Size => "-Os",
+            OptLevel::SizeMin => "-Oz",
+        };
+    }
+
+    fn output_filename(&mut self, path: &Path) {
+        self.cmd.arg("-o").arg(path);
+    }
+
+    fn framework_path(&mut self, _path: &Path) {
+        panic!("frameworks not supported")
+    }
+
+    fn full_relro(&mut self) {}
+
+    fn partial_relro(&mut self) {}
+
+    fn no_relro(&mut self) {}
+
+    fn gc_sections(&mut self, _keep_metadata: bool) {}
+
+    fn no_gc_sections(&mut self) {}
+
+    fn pgo_gen(&mut self) {}
+
+    fn no_crt_objects(&mut self) {}
+
+    fn no_default_libraries(&mut self) {}
+
+    fn control_flow_guard(&mut self) {}
+
+    fn ehcont_guard(&mut self) {}
+
+    fn export_symbols(&mut self, _tmpdir: &Path, _crate_type: CrateType, symbols: &[String]) {
+        match _crate_type {
+            CrateType::Cdylib => {
+                for sym in symbols {
+                    self.cmd.arg("--export-symbol").arg(sym);
+                }
+            }
+            _ => (),
+        }
+    }
+
+    fn subsystem(&mut self, _subsystem: &str) {}
+
+    fn linker_plugin_lto(&mut self) {}
+}
+
 pub struct BpfLinker<'a> {
     cmd: Command,
     sess: &'a Session,

compiler/rustc_codegen_ssa/src/back/write.rs

@@ -374,6 +374,10 @@ pub struct CodegenContext<B: WriteBackendMethods> {
     pub incr_comp_session_dir: Option<PathBuf>,
     /// Channel back to the main control thread to send messages to
     pub coordinator_send: Sender<Box<dyn Any + Send>>,
+    /// `true` if the codegen should be run in parallel.
+    ///
+    /// Depends on [`CodegenBackend::supports_parallel()`] and `-Zno_parallel_backend`.
+    pub parallel: bool,
 }
 
 impl<B: WriteBackendMethods> CodegenContext<B> {
@@ -1152,6 +1156,7 @@ fn start_executing_work<B: ExtraBackendMethods>(
         target_arch: tcx.sess.target.arch.to_string(),
         split_debuginfo: tcx.sess.split_debuginfo(),
         split_dwarf_kind: tcx.sess.opts.unstable_opts.split_dwarf_kind,
+        parallel: backend.supports_parallel() && !sess.opts.unstable_opts.no_parallel_backend,
     };
 
     // This is the "main loop" of parallel work happening for parallel codegen.
@@ -1422,7 +1427,7 @@ fn start_executing_work<B: ExtraBackendMethods>(
                             .binary_search_by_key(&cost, |&(_, cost)| cost)
                             .unwrap_or_else(|e| e);
                         work_items.insert(insertion_index, (work, cost));
-                        if !cgcx.opts.unstable_opts.no_parallel_llvm {
+                        if cgcx.parallel {
                             helper.request_token();
                         }
                     }
@@ -1545,7 +1550,7 @@ fn start_executing_work<B: ExtraBackendMethods>(
                     };
                     work_items.insert(insertion_index, (llvm_work_item, cost));
 
-                    if !cgcx.opts.unstable_opts.no_parallel_llvm {
+                    if cgcx.parallel {
                         helper.request_token();
                     }
                     assert_eq!(main_thread_state, MainThreadState::Codegenning);

compiler/rustc_codegen_ssa/src/base.rs

@@ -165,14 +165,11 @@ pub fn unsized_info<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
                 cx.tcx().vtable_trait_upcasting_coercion_new_vptr_slot((source, target));
 
             if let Some(entry_idx) = vptr_entry_idx {
-                let ptr_ty = cx.type_ptr();
-                let ptr_align = cx.tcx().data_layout.pointer_align.abi;
-                let gep = bx.inbounds_gep(
-                    ptr_ty,
-                    old_info,
-                    &[bx.const_usize(u64::try_from(entry_idx).unwrap())],
-                );
-                let new_vptr = bx.load(ptr_ty, gep, ptr_align);
+                let ptr_size = bx.data_layout().pointer_size;
+                let ptr_align = bx.data_layout().pointer_align.abi;
+                let vtable_byte_offset = u64::try_from(entry_idx).unwrap() * ptr_size.bytes();
+                let gep = bx.inbounds_ptradd(old_info, bx.const_usize(vtable_byte_offset));
+                let new_vptr = bx.load(bx.type_ptr(), gep, ptr_align);
                 bx.nonnull_metadata(new_vptr);
                 // VTable loads are invariant.
                 bx.set_invariant_load(new_vptr);

compiler/rustc_codegen_ssa/src/meth.rs

@@ -20,9 +20,13 @@ impl<'a, 'tcx> VirtualIndex {
         ty: Ty<'tcx>,
         fn_abi: &FnAbi<'tcx, Ty<'tcx>>,
     ) -> Bx::Value {
-        // Load the data pointer from the object.
+        // Load the function pointer from the object.
         debug!("get_fn({llvtable:?}, {ty:?}, {self:?})");
+
         let llty = bx.fn_ptr_backend_type(fn_abi);
+        let ptr_size = bx.data_layout().pointer_size;
+        let ptr_align = bx.data_layout().pointer_align.abi;
+        let vtable_byte_offset = self.0 * ptr_size.bytes();
 
         if bx.cx().sess().opts.unstable_opts.virtual_function_elimination
             && bx.cx().sess().lto() == Lto::Fat
@@ -30,12 +34,10 @@ impl<'a, 'tcx> VirtualIndex {
             let typeid = bx
                 .typeid_metadata(typeid_for_trait_ref(bx.tcx(), expect_dyn_trait_in_self(ty)))
                 .unwrap();
-            let vtable_byte_offset = self.0 * bx.data_layout().pointer_size.bytes();
             let func = bx.type_checked_load(llvtable, vtable_byte_offset, typeid);
             func
         } else {
-            let ptr_align = bx.tcx().data_layout.pointer_align.abi;
-            let gep = bx.inbounds_gep(llty, llvtable, &[bx.const_usize(self.0)]);
+            let gep = bx.inbounds_ptradd(llvtable, bx.const_usize(vtable_byte_offset));
             let ptr = bx.load(llty, gep, ptr_align);
             bx.nonnull_metadata(ptr);
             // VTable loads are invariant.
@@ -53,9 +55,12 @@ impl<'a, 'tcx> VirtualIndex {
         debug!("get_int({:?}, {:?})", llvtable, self);
 
         let llty = bx.type_isize();
-        let usize_align = bx.tcx().data_layout.pointer_align.abi;
-        let gep = bx.inbounds_gep(llty, llvtable, &[bx.const_usize(self.0)]);
-        let ptr = bx.load(llty, gep, usize_align);
+        let ptr_size = bx.data_layout().pointer_size;
+        let ptr_align = bx.data_layout().pointer_align.abi;
+        let vtable_byte_offset = self.0 * ptr_size.bytes();
+
+        let gep = bx.inbounds_ptradd(llvtable, bx.const_usize(vtable_byte_offset));
+        let ptr = bx.load(llty, gep, ptr_align);
         // VTable loads are invariant.
         bx.set_invariant_load(ptr);
         ptr

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -1597,7 +1597,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         let funclet;
         let llbb;
         let mut bx;
-        if base::wants_msvc_seh(self.cx.sess()) {
+        if base::wants_new_eh_instructions(self.cx.sess()) {
             // This is a basic block that we're aborting the program for,
             // notably in an `extern` function. These basic blocks are inserted
             // so that we assert that `extern` functions do indeed not panic,

compiler/rustc_codegen_ssa/src/traits/backend.rs

@@ -111,6 +111,13 @@ pub trait CodegenBackend {
         codegen_results: CodegenResults,
         outputs: &OutputFilenames,
     ) -> Result<(), ErrorGuaranteed>;
+
+    /// Returns `true` if this backend can be safely called from multiple threads.
+    ///
+    /// Defaults to `true`.
+    fn supports_parallel(&self) -> bool {
+        true
+    }
 }
 
 pub trait ExtraBackendMethods:

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

@@ -380,16 +380,12 @@ pub fn eval_in_interpreter<'mir, 'tcx>(
         }
         Ok(mplace) => {
             // Since evaluation had no errors, validate the resulting constant.
-
-            // Temporarily allow access to the static_root_alloc_id for the purpose of validation.
-            let static_root_alloc_id = ecx.machine.static_root_alloc_id.take();
-            let validation = const_validate_mplace(&ecx, &mplace, cid);
-            ecx.machine.static_root_alloc_id = static_root_alloc_id;
+            let res = const_validate_mplace(&ecx, &mplace, cid);
 
             let alloc_id = mplace.ptr().provenance.unwrap().alloc_id();
 
             // Validation failed, report an error.
-            if let Err(error) = validation {
+            if let Err(error) = res {
                 Err(const_report_error(&ecx, error, alloc_id))
             } else {
                 // Convert to raw constant
@@ -412,10 +408,10 @@ pub fn const_validate_mplace<'mir, 'tcx>(
             _ if cid.promoted.is_some() => CtfeValidationMode::Promoted,
             Some(mutbl) => CtfeValidationMode::Static { mutbl }, // a `static`
             None => {
-                // In normal `const` (not promoted), the outermost allocation is always only copied,
-                // so having `UnsafeCell` in there is okay despite them being in immutable memory.
-                let allow_immutable_unsafe_cell = cid.promoted.is_none() && !inner;
-                CtfeValidationMode::Const { allow_immutable_unsafe_cell }
+                // This is a normal `const` (not promoted).
+                // The outermost allocation is always only copied, so having `UnsafeCell` in there
+                // is okay despite them being in immutable memory.
+                CtfeValidationMode::Const { allow_immutable_unsafe_cell: !inner }
             }
         };
         ecx.const_validate_operand(&mplace.into(), path, &mut ref_tracking, mode)?;

compiler/rustc_const_eval/src/interpret/machine.rs

@@ -391,6 +391,8 @@ pub trait Machine<'mir, 'tcx: 'mir>: Sized {
 
     /// Hook for performing extra checks on a memory read access.
     ///
+    /// This will *not* be called during validation!
+    ///
     /// Takes read-only access to the allocation so we can keep all the memory read
     /// operations take `&self`. Use a `RefCell` in `AllocExtra` if you
     /// need to mutate.
@@ -410,6 +412,8 @@ pub trait Machine<'mir, 'tcx: 'mir>: Sized {
     /// Hook for performing extra checks on any memory read access,
     /// that involves an allocation, even ZST reads.
     ///
+    /// This will *not* be called during validation!
+    ///
     /// Used to prevent statics from self-initializing by reading from their own memory
     /// as it is being initialized.
     fn before_alloc_read(

compiler/rustc_const_eval/src/interpret/memory.rs

@@ -8,6 +8,7 @@
 
 use std::assert_matches::assert_matches;
 use std::borrow::Cow;
+use std::cell::Cell;
 use std::collections::VecDeque;
 use std::fmt;
 use std::ptr;
@@ -111,6 +112,11 @@ pub struct Memory<'mir, 'tcx, M: Machine<'mir, 'tcx>> {
     /// that do not exist any more.
     // FIXME: this should not be public, but interning currently needs access to it
     pub(super) dead_alloc_map: FxIndexMap<AllocId, (Size, Align)>,
+
+    /// This stores whether we are currently doing reads purely for the purpose of validation.
+    /// Those reads do not trigger the machine's hooks for memory reads.
+    /// Needless to say, this must only be set with great care!
+    validation_in_progress: Cell<bool>,
 }
 
 /// A reference to some allocation that was already bounds-checked for the given region
@@ -137,6 +143,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
             alloc_map: M::MemoryMap::default(),
             extra_fn_ptr_map: FxIndexMap::default(),
             dead_alloc_map: FxIndexMap::default(),
+            validation_in_progress: Cell::new(false),
         }
     }
 
@@ -624,10 +631,12 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             size,
             CheckInAllocMsg::MemoryAccessTest,
             |alloc_id, offset, prov| {
-                // We want to call the hook on *all* accesses that involve an AllocId,
-                // including zero-sized accesses. That means we have to do it here
-                // rather than below in the `Some` branch.
-                M::before_alloc_read(self, alloc_id)?;
+                if !self.memory.validation_in_progress.get() {
+                    // We want to call the hook on *all* accesses that involve an AllocId,
+                    // including zero-sized accesses. That means we have to do it here
+                    // rather than below in the `Some` branch.
+                    M::before_alloc_read(self, alloc_id)?;
+                }
                 let alloc = self.get_alloc_raw(alloc_id)?;
                 Ok((alloc.size(), alloc.align, (alloc_id, offset, prov, alloc)))
             },
@@ -635,7 +644,15 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
         if let Some((alloc_id, offset, prov, alloc)) = ptr_and_alloc {
             let range = alloc_range(offset, size);
-            M::before_memory_read(self.tcx, &self.machine, &alloc.extra, (alloc_id, prov), range)?;
+            if !self.memory.validation_in_progress.get() {
+                M::before_memory_read(
+                    self.tcx,
+                    &self.machine,
+                    &alloc.extra,
+                    (alloc_id, prov),
+                    range,
+                )?;
+            }
             Ok(Some(AllocRef { alloc, range, tcx: *self.tcx, alloc_id }))
         } else {
             Ok(None)
@@ -909,6 +926,21 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             }
         })
     }
+
+    /// Runs the close in "validation" mode, which means the machine's memory read hooks will be
+    /// suppressed. Needless to say, this must only be set with great care! Cannot be nested.
+    pub(super) fn run_for_validation<R>(&self, f: impl FnOnce() -> R) -> R {
+        assert!(
+            self.memory.validation_in_progress.replace(true) == false,
+            "`validation_in_progress` was already set"
+        );
+        let res = f();
+        assert!(
+            self.memory.validation_in_progress.replace(false) == true,
+            "`validation_in_progress` was unset by someone else"
+        );
+        res
+    }
 }
 
 #[doc(hidden)]
@@ -1154,6 +1186,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         };
         let src_alloc = self.get_alloc_raw(src_alloc_id)?;
         let src_range = alloc_range(src_offset, size);
+        assert!(!self.memory.validation_in_progress.get(), "we can't be copying during validation");
         M::before_memory_read(
             tcx,
             &self.machine,

compiler/rustc_const_eval/src/interpret/validity.rs

@@ -971,7 +971,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         let mut visitor = ValidityVisitor { path, ref_tracking, ctfe_mode, ecx: self };
 
         // Run it.
-        match visitor.visit_value(op) {
+        match self.run_for_validation(|| visitor.visit_value(op)) {
             Ok(()) => Ok(()),
             // Pass through validation failures and "invalid program" issues.
             Err(err)

compiler/rustc_const_eval/src/transform/check_consts/check.rs

@@ -30,7 +30,7 @@ type QualifResults<'mir, 'tcx, Q> =
     rustc_mir_dataflow::ResultsCursor<'mir, 'tcx, FlowSensitiveAnalysis<'mir, 'mir, 'tcx, Q>>;
 
 #[derive(Default)]
-pub struct Qualifs<'mir, 'tcx> {
+pub(crate) struct Qualifs<'mir, 'tcx> {
     has_mut_interior: Option<QualifResults<'mir, 'tcx, HasMutInterior>>,
     needs_drop: Option<QualifResults<'mir, 'tcx, NeedsDrop>>,
     needs_non_const_drop: Option<QualifResults<'mir, 'tcx, NeedsNonConstDrop>>,

compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs

@@ -284,6 +284,7 @@ where
                 if Q::in_adt_inherently(cx, def, args) {
                     return true;
                 }
+                // Don't do any value-based reasoning for unions.
                 if def.is_union() && Q::in_any_value_of_ty(cx, rvalue.ty(cx.body, cx.tcx)) {
                     return true;
                 }

compiler/rustc_driver_impl/src/lib.rs

@@ -37,7 +37,7 @@ use rustc_session::config::{nightly_options, CG_OPTIONS, Z_OPTIONS};
 use rustc_session::config::{ErrorOutputType, Input, OutFileName, OutputType};
 use rustc_session::getopts::{self, Matches};
 use rustc_session::lint::{Lint, LintId};
-use rustc_session::{config, EarlyDiagCtxt, Session};
+use rustc_session::{config, filesearch, EarlyDiagCtxt, Session};
 use rustc_span::def_id::LOCAL_CRATE;
 use rustc_span::source_map::FileLoader;
 use rustc_span::symbol::sym;
@@ -887,7 +887,11 @@ pub fn version_at_macro_invocation(
 
         let debug_flags = matches.opt_strs("Z");
         let backend_name = debug_flags.iter().find_map(|x| x.strip_prefix("codegen-backend="));
-        get_codegen_backend(early_dcx, &None, backend_name).print_version();
+        let opts = config::Options::default();
+        let sysroot = filesearch::materialize_sysroot(opts.maybe_sysroot.clone());
+        let target = config::build_target_config(early_dcx, &opts, None, &sysroot);
+
+        get_codegen_backend(early_dcx, &sysroot, backend_name, &target).print_version();
     }
 }
 
@@ -1092,7 +1096,12 @@ pub fn describe_flag_categories(early_dcx: &EarlyDiagCtxt, matches: &Matches) ->
 
     if cg_flags.iter().any(|x| *x == "passes=list") {
         let backend_name = debug_flags.iter().find_map(|x| x.strip_prefix("codegen-backend="));
-        get_codegen_backend(early_dcx, &None, backend_name).print_passes();
+
+        let opts = config::Options::default();
+        let sysroot = filesearch::materialize_sysroot(opts.maybe_sysroot.clone());
+        let target = config::build_target_config(early_dcx, &opts, None, &sysroot);
+
+        get_codegen_backend(early_dcx, &sysroot, backend_name, &target).print_passes();
         return true;
     }
 

compiler/rustc_errors/src/lib.rs

@@ -442,8 +442,8 @@ struct DiagCtxtInner {
     emitter: Box<DynEmitter>,
 
     /// Must we produce a diagnostic to justify the use of the expensive
-    /// `trimmed_def_paths` function?
-    must_produce_diag: bool,
+    /// `trimmed_def_paths` function? Backtrace is the location of the call.
+    must_produce_diag: Option<Backtrace>,
 
     /// Has this diagnostic context printed any diagnostics? (I.e. has
     /// `self.emitter.emit_diagnostic()` been called?
@@ -572,10 +572,11 @@ impl Drop for DiagCtxtInner {
         }
 
         if !self.has_printed && !self.suppressed_expected_diag && !std::thread::panicking() {
-            if self.must_produce_diag {
+            if let Some(backtrace) = &self.must_produce_diag {
                 panic!(
-                    "must_produce_diag: trimmed_def_paths called but no diagnostics emitted; \
-                       use `DelayDm` for lints or `with_no_trimmed_paths` for debugging"
+                    "must_produce_diag: `trimmed_def_paths` called but no diagnostics emitted; \
+                       use `DelayDm` for lints or `with_no_trimmed_paths` for debugging. \
+                       called at: {backtrace}"
                 );
             }
         }
@@ -721,7 +722,7 @@ impl DiagCtxt {
         *delayed_bugs = Default::default();
         *deduplicated_err_count = 0;
         *deduplicated_warn_count = 0;
-        *must_produce_diag = false;
+        *must_produce_diag = None;
         *has_printed = false;
         *suppressed_expected_diag = false;
         *taught_diagnostics = Default::default();
@@ -1091,8 +1092,13 @@ impl DiagCtxt {
 
     /// Used when trimmed_def_paths is called and we must produce a diagnostic
     /// to justify its cost.
+    #[track_caller]
     pub fn set_must_produce_diag(&self) {
-        self.inner.borrow_mut().must_produce_diag = true;
+        assert!(
+            self.inner.borrow().must_produce_diag.is_none(),
+            "should only need to collect a backtrace once"
+        );
+        self.inner.borrow_mut().must_produce_diag = Some(Backtrace::capture());
     }
 }
 
@@ -1384,7 +1390,7 @@ impl DiagCtxtInner {
             deduplicated_err_count: 0,
             deduplicated_warn_count: 0,
             emitter,
-            must_produce_diag: false,
+            must_produce_diag: None,
             has_printed: false,
             suppressed_expected_diag: false,
             taught_diagnostics: Default::default(),

compiler/rustc_hir_analysis/src/astconv/bounds.rs

@@ -408,7 +408,7 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
             // Create the generic arguments for the associated type or constant by joining the
             // parent arguments (the arguments of the trait) and the own arguments (the ones of
             // the associated item itself) and construct an alias type using them.
-            candidate.map_bound(|trait_ref| {
+            let alias_ty = candidate.map_bound(|trait_ref| {
                 let ident = Ident::new(assoc_item.name, binding.ident.span);
                 let item_segment = hir::PathSegment {
                     ident,
@@ -430,7 +430,25 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
                 // *constants* to represent *const projections*. Alias *term* would be a more
                 // appropriate name but alas.
                 ty::AliasTy::new(tcx, assoc_item.def_id, alias_args)
-            })
+            });
+
+            // Provide the resolved type of the associated constant to `type_of(AnonConst)`.
+            if !speculative
+                && let hir::TypeBindingKind::Equality { term: hir::Term::Const(anon_const) } =
+                    binding.kind
+            {
+                let ty = alias_ty.map_bound(|ty| tcx.type_of(ty.def_id).instantiate(tcx, ty.args));
+                // Since the arguments passed to the alias type above may contain early-bound
+                // generic parameters, the instantiated type may contain some as well.
+                // Therefore wrap it in `EarlyBinder`.
+                // FIXME(fmease): Reject escaping late-bound vars.
+                tcx.feed_anon_const_type(
+                    anon_const.def_id,
+                    ty::EarlyBinder::bind(ty.skip_binder()),
+                );
+            }
+
+            alias_ty
         };
 
         match binding.kind {

compiler/rustc_hir_analysis/src/collect/type_of.rs

@@ -79,37 +79,6 @@ fn anon_const_type_of<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Ty<'tcx> {
                 .expect("const parameter types cannot be generic");
         }
 
-        Node::TypeBinding(binding @ &TypeBinding { hir_id: binding_id, .. })
-            if let Node::TraitRef(trait_ref) = tcx.parent_hir_node(binding_id) =>
-        {
-            let Some(trait_def_id) = trait_ref.trait_def_id() else {
-                return Ty::new_error_with_message(
-                    tcx,
-                    tcx.def_span(def_id),
-                    "Could not find trait",
-                );
-            };
-            let assoc_items = tcx.associated_items(trait_def_id);
-            let assoc_item = assoc_items.find_by_name_and_kind(
-                tcx,
-                binding.ident,
-                ty::AssocKind::Const,
-                def_id.to_def_id(),
-            );
-            return if let Some(assoc_item) = assoc_item {
-                tcx.type_of(assoc_item.def_id)
-                    .no_bound_vars()
-                    .expect("const parameter types cannot be generic")
-            } else {
-                // FIXME(associated_const_equality): add a useful error message here.
-                Ty::new_error_with_message(
-                    tcx,
-                    tcx.def_span(def_id),
-                    "Could not find associated const on trait",
-                )
-            };
-        }
-
         // This match arm is for when the def_id appears in a GAT whose
         // path can't be resolved without typechecking e.g.
         //

compiler/rustc_interface/src/interface.rs

@@ -16,7 +16,7 @@ use rustc_parse::maybe_new_parser_from_source_str;
 use rustc_query_impl::QueryCtxt;
 use rustc_query_system::query::print_query_stack;
 use rustc_session::config::{self, Cfg, CheckCfg, ExpectedValues, Input, OutFileName};
-use rustc_session::filesearch::sysroot_candidates;
+use rustc_session::filesearch::{self, sysroot_candidates};
 use rustc_session::parse::ParseSess;
 use rustc_session::{lint, CompilerIO, EarlyDiagCtxt, Session};
 use rustc_span::source_map::FileLoader;
@@ -339,16 +339,53 @@ pub fn run_compiler<R: Send>(config: Config, f: impl FnOnce(&Compiler) -> R + Se
 
             let early_dcx = EarlyDiagCtxt::new(config.opts.error_format);
 
-            let codegen_backend = if let Some(make_codegen_backend) = config.make_codegen_backend {
-                make_codegen_backend(&config.opts)
-            } else {
-                util::get_codegen_backend(
-                    &early_dcx,
-                    &config.opts.maybe_sysroot,
-                    config.opts.unstable_opts.codegen_backend.as_deref(),
-                )
+            let sysroot = filesearch::materialize_sysroot(config.opts.maybe_sysroot.clone());
+
+            let (codegen_backend, target_override) = match config.make_codegen_backend {
+                None => {
+                    // Build a target without override, so that it can override the backend if needed
+                    let target =
+                        config::build_target_config(&early_dcx, &config.opts, None, &sysroot);
+
+                    let backend = util::get_codegen_backend(
+                        &early_dcx,
+                        &sysroot,
+                        config.opts.unstable_opts.codegen_backend.as_deref(),
+                        &target,
+                    );
+
+                    // target_override is documented to be called before init(), so this is okay
+                    let target_override = backend.target_override(&config.opts);
+
+                    // Assert that we don't use target's override of the backend and
+                    // backend's override of the target at the same time
+                    if config.opts.unstable_opts.codegen_backend.is_none()
+                        && target.default_codegen_backend.is_some()
+                        && target_override.is_some()
+                    {
+                        rustc_middle::bug!(
+                            "Codegen backend requested target override even though the target requested the backend"
+                        );
+                    }
+
+                    (backend, target_override)
+                }
+                Some(make_codegen_backend) => {
+                    // N.B. `make_codegen_backend` takes precedence over `target.default_codegen_backend`,
+                    //      which is ignored in this case.
+                    let backend = make_codegen_backend(&config.opts);
+
+                    // target_override is documented to be called before init(), so this is okay
+                    let target_override = backend.target_override(&config.opts);
+
+                    (backend, target_override)
+                }
             };
 
+            // Re-build target with the (potential) override
+            let target_cfg =
+                config::build_target_config(&early_dcx, &config.opts, target_override, &sysroot);
+
             let temps_dir = config.opts.unstable_opts.temps_dir.as_deref().map(PathBuf::from);
 
             let bundle = match rustc_errors::fluent_bundle(
@@ -367,9 +404,6 @@ pub fn run_compiler<R: Send>(config: Config, f: impl FnOnce(&Compiler) -> R + Se
             let mut locale_resources = Vec::from(config.locale_resources);
             locale_resources.push(codegen_backend.locale_resource());
 
-            // target_override is documented to be called before init(), so this is okay
-            let target_override = codegen_backend.target_override(&config.opts);
-
             let mut sess = rustc_session::build_session(
                 early_dcx,
                 config.opts,
@@ -384,7 +418,8 @@ pub fn run_compiler<R: Send>(config: Config, f: impl FnOnce(&Compiler) -> R + Se
                 locale_resources,
                 config.lint_caps,
                 config.file_loader,
-                target_override,
+                target_cfg,
+                sysroot,
                 util::rustc_version_str().unwrap_or("unknown"),
                 config.ice_file,
                 config.using_internal_features,

compiler/rustc_interface/src/tests.rs

@@ -13,7 +13,7 @@ use rustc_session::config::{
 use rustc_session::lint::Level;
 use rustc_session::search_paths::SearchPath;
 use rustc_session::utils::{CanonicalizedPath, NativeLib, NativeLibKind};
-use rustc_session::{build_session, getopts, CompilerIO, EarlyDiagCtxt, Session};
+use rustc_session::{build_session, filesearch, getopts, CompilerIO, EarlyDiagCtxt, Session};
 use rustc_span::edition::{Edition, DEFAULT_EDITION};
 use rustc_span::symbol::sym;
 use rustc_span::{FileName, SourceFileHashAlgorithm};
@@ -37,6 +37,12 @@ fn mk_session(matches: getopts::Matches) -> (Session, Cfg) {
         output_file: None,
         temps_dir,
     };
+
+    let sysroot = filesearch::materialize_sysroot(sessopts.maybe_sysroot.clone());
+
+    let target_cfg =
+        rustc_session::config::build_target_config(&early_dcx, &sessopts, None, &sysroot);
+
     let sess = build_session(
         early_dcx,
         sessopts,
@@ -46,7 +52,8 @@ fn mk_session(matches: getopts::Matches) -> (Session, Cfg) {
         vec![],
         Default::default(),
         None,
-        None,
+        target_cfg,
+        sysroot,
         "",
         None,
         Arc::default(),
@@ -685,7 +692,7 @@ fn test_unstable_options_tracking_hash() {
     untracked!(nll_facts, true);
     untracked!(no_analysis, true);
     untracked!(no_leak_check, true);
-    untracked!(no_parallel_llvm, true);
+    untracked!(no_parallel_backend, true);
     untracked!(parse_only, true);
     // `pre_link_arg` is omitted because it just forwards to `pre_link_args`.
     untracked!(pre_link_args, vec![String::from("abc"), String::from("def")]);

compiler/rustc_interface/src/util.rs

@@ -14,13 +14,14 @@ use rustc_session::{filesearch, output, Session};
 use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::edition::Edition;
 use rustc_span::symbol::{sym, Symbol};
+use rustc_target::spec::Target;
 use session::EarlyDiagCtxt;
-use std::env;
 use std::env::consts::{DLL_PREFIX, DLL_SUFFIX};
 use std::path::{Path, PathBuf};
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::OnceLock;
 use std::thread;
+use std::{env, iter};
 
 /// Function pointer type that constructs a new CodegenBackend.
 pub type MakeBackendFn = fn() -> Box<dyn CodegenBackend>;
@@ -195,21 +196,25 @@ fn load_backend_from_dylib(early_dcx: &EarlyDiagCtxt, path: &Path) -> MakeBacken
 /// A name of `None` indicates that the default backend should be used.
 pub fn get_codegen_backend(
     early_dcx: &EarlyDiagCtxt,
-    maybe_sysroot: &Option<PathBuf>,
+    sysroot: &Path,
     backend_name: Option<&str>,
+    target: &Target,
 ) -> Box<dyn CodegenBackend> {
     static LOAD: OnceLock<unsafe fn() -> Box<dyn CodegenBackend>> = OnceLock::new();
 
     let load = LOAD.get_or_init(|| {
-        let default_codegen_backend = option_env!("CFG_DEFAULT_CODEGEN_BACKEND").unwrap_or("llvm");
+        let backend = backend_name
+            .or(target.default_codegen_backend.as_deref())
+            .or(option_env!("CFG_DEFAULT_CODEGEN_BACKEND"))
+            .unwrap_or("llvm");
 
-        match backend_name.unwrap_or(default_codegen_backend) {
+        match backend {
             filename if filename.contains('.') => {
                 load_backend_from_dylib(early_dcx, filename.as_ref())
             }
             #[cfg(feature = "llvm")]
             "llvm" => rustc_codegen_llvm::LlvmCodegenBackend::new,
-            backend_name => get_codegen_sysroot(early_dcx, maybe_sysroot, backend_name),
+            backend_name => get_codegen_sysroot(early_dcx, sysroot, backend_name),
         }
     });
 
@@ -244,7 +249,7 @@ fn get_rustc_path_inner(bin_path: &str) -> Option<PathBuf> {
 #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
 fn get_codegen_sysroot(
     early_dcx: &EarlyDiagCtxt,
-    maybe_sysroot: &Option<PathBuf>,
+    sysroot: &Path,
     backend_name: &str,
 ) -> MakeBackendFn {
     // For now we only allow this function to be called once as it'll dlopen a
@@ -261,28 +266,28 @@ fn get_codegen_sysroot(
     let target = session::config::host_triple();
     let sysroot_candidates = sysroot_candidates();
 
-    let sysroot = maybe_sysroot
-        .iter()
-        .chain(sysroot_candidates.iter())
+    let sysroot = iter::once(sysroot)
+        .chain(sysroot_candidates.iter().map(<_>::as_ref))
         .map(|sysroot| {
             filesearch::make_target_lib_path(sysroot, target).with_file_name("codegen-backends")
         })
         .find(|f| {
             info!("codegen backend candidate: {}", f.display());
             f.exists()
-        });
-    let sysroot = sysroot.unwrap_or_else(|| {
-        let candidates = sysroot_candidates
-            .iter()
-            .map(|p| p.display().to_string())
-            .collect::<Vec<_>>()
-            .join("\n* ");
-        let err = format!(
-            "failed to find a `codegen-backends` folder \
+        })
+        .unwrap_or_else(|| {
+            let candidates = sysroot_candidates
+                .iter()
+                .map(|p| p.display().to_string())
+                .collect::<Vec<_>>()
+                .join("\n* ");
+            let err = format!(
+                "failed to find a `codegen-backends` folder \
                            in the sysroot candidates:\n* {candidates}"
-        );
-        early_dcx.early_fatal(err);
-    });
+            );
+            early_dcx.early_fatal(err);
+        });
+
     info!("probing {} for a codegen backend", sysroot.display());
 
     let d = sysroot.read_dir().unwrap_or_else(|e| {

compiler/rustc_mir_build/src/build/scope.rs

@@ -203,16 +203,31 @@ const ROOT_NODE: DropIdx = DropIdx::from_u32(0);
 /// in `build_mir`.
 #[derive(Debug)]
 struct DropTree {
-    /// Drops in the tree.
-    drops: IndexVec<DropIdx, (DropData, DropIdx)>,
-    /// Map for finding the inverse of the `next_drop` relation:
-    ///
-    /// `previous_drops[(drops[i].1, drops[i].0.local, drops[i].0.kind)] == i`
-    previous_drops: FxHashMap<(DropIdx, Local, DropKind), DropIdx>,
+    /// Nodes in the drop tree, containing drop data and a link to the next node.
+    drops: IndexVec<DropIdx, DropNode>,
+    /// Map for finding the index of an existing node, given its contents.
+    existing_drops_map: FxHashMap<DropNodeKey, DropIdx>,
     /// Edges into the `DropTree` that need to be added once it's lowered.
     entry_points: Vec<(DropIdx, BasicBlock)>,
 }
 
+/// A single node in the drop tree.
+#[derive(Debug)]
+struct DropNode {
+    /// Info about the drop to be performed at this node in the drop tree.
+    data: DropData,
+    /// Index of the "next" drop to perform (in drop order, not declaration order).
+    next: DropIdx,
+}
+
+/// Subset of [`DropNode`] used for reverse lookup in a hash table.
+#[derive(Debug, PartialEq, Eq, Hash)]
+struct DropNodeKey {
+    next: DropIdx,
+    local: Local,
+    kind: DropKind,
+}
+
 impl Scope {
     /// Whether there's anything to do for the cleanup path, that is,
     /// when unwinding through this scope. This includes destructors,
@@ -247,7 +262,7 @@ trait DropTreeBuilder<'tcx> {
 
     /// Links a block outside the drop tree, `from`, to the block `to` inside
     /// the drop tree.
-    fn add_entry(cfg: &mut CFG<'tcx>, from: BasicBlock, to: BasicBlock);
+    fn link_entry_point(cfg: &mut CFG<'tcx>, from: BasicBlock, to: BasicBlock);
 }
 
 impl DropTree {
@@ -258,20 +273,29 @@ impl DropTree {
         let fake_source_info = SourceInfo::outermost(DUMMY_SP);
         let fake_data =
             DropData { source_info: fake_source_info, local: Local::MAX, kind: DropKind::Storage };
-        let drop_idx = DropIdx::MAX;
-        let drops = IndexVec::from_elem_n((fake_data, drop_idx), 1);
-        Self { drops, entry_points: Vec::new(), previous_drops: FxHashMap::default() }
+        let drops = IndexVec::from_raw(vec![DropNode { data: fake_data, next: DropIdx::MAX }]);
+        Self { drops, entry_points: Vec::new(), existing_drops_map: FxHashMap::default() }
     }
 
-    fn add_drop(&mut self, drop: DropData, next: DropIdx) -> DropIdx {
+    /// Adds a node to the drop tree, consisting of drop data and the index of
+    /// the "next" drop (in drop order), which could be the sentinel [`ROOT_NODE`].
+    ///
+    /// If there is already an equivalent node in the tree, nothing is added, and
+    /// that node's index is returned. Otherwise, the new node's index is returned.
+    fn add_drop(&mut self, data: DropData, next: DropIdx) -> DropIdx {
         let drops = &mut self.drops;
         *self
-            .previous_drops
-            .entry((next, drop.local, drop.kind))
-            .or_insert_with(|| drops.push((drop, next)))
+            .existing_drops_map
+            .entry(DropNodeKey { next, local: data.local, kind: data.kind })
+            // Create a new node, and also add its index to the map.
+            .or_insert_with(|| drops.push(DropNode { data, next }))
     }
 
-    fn add_entry(&mut self, from: BasicBlock, to: DropIdx) {
+    /// Registers `from` as an entry point to this drop tree, at `to`.
+    ///
+    /// During [`Self::build_mir`], `from` will be linked to the corresponding
+    /// block within the drop tree.
+    fn add_entry_point(&mut self, from: BasicBlock, to: DropIdx) {
         debug_assert!(to < self.drops.next_index());
         self.entry_points.push((to, from));
     }
@@ -326,13 +350,13 @@ impl DropTree {
         let entry_points = &mut self.entry_points;
         entry_points.sort();
 
-        for (drop_idx, drop_data) in self.drops.iter_enumerated().rev() {
+        for (drop_idx, drop_node) in self.drops.iter_enumerated().rev() {
             if entry_points.last().is_some_and(|entry_point| entry_point.0 == drop_idx) {
                 let block = *blocks[drop_idx].get_or_insert_with(|| T::make_block(cfg));
                 needs_block[drop_idx] = Block::Own;
                 while entry_points.last().is_some_and(|entry_point| entry_point.0 == drop_idx) {
                     let entry_block = entry_points.pop().unwrap().1;
-                    T::add_entry(cfg, entry_block, block);
+                    T::link_entry_point(cfg, entry_block, block);
                 }
             }
             match needs_block[drop_idx] {
@@ -344,10 +368,10 @@ impl DropTree {
                     blocks[drop_idx] = blocks[pred];
                 }
             }
-            if let DropKind::Value = drop_data.0.kind {
-                needs_block[drop_data.1] = Block::Own;
+            if let DropKind::Value = drop_node.data.kind {
+                needs_block[drop_node.next] = Block::Own;
             } else if drop_idx != ROOT_NODE {
-                match &mut needs_block[drop_data.1] {
+                match &mut needs_block[drop_node.next] {
                     pred @ Block::None => *pred = Block::Shares(drop_idx),
                     pred @ Block::Shares(_) => *pred = Block::Own,
                     Block::Own => (),
@@ -364,34 +388,35 @@ impl DropTree {
         cfg: &mut CFG<'tcx>,
         blocks: &IndexSlice<DropIdx, Option<BasicBlock>>,
     ) {
-        for (drop_idx, drop_data) in self.drops.iter_enumerated().rev() {
+        for (drop_idx, drop_node) in self.drops.iter_enumerated().rev() {
             let Some(block) = blocks[drop_idx] else { continue };
-            match drop_data.0.kind {
+            match drop_node.data.kind {
                 DropKind::Value => {
                     let terminator = TerminatorKind::Drop {
-                        target: blocks[drop_data.1].unwrap(),
+                        target: blocks[drop_node.next].unwrap(),
                         // The caller will handle this if needed.
                         unwind: UnwindAction::Terminate(UnwindTerminateReason::InCleanup),
-                        place: drop_data.0.local.into(),
+                        place: drop_node.data.local.into(),
                         replace: false,
                     };
-                    cfg.terminate(block, drop_data.0.source_info, terminator);
+                    cfg.terminate(block, drop_node.data.source_info, terminator);
                 }
                 // Root nodes don't correspond to a drop.
                 DropKind::Storage if drop_idx == ROOT_NODE => {}
                 DropKind::Storage => {
                     let stmt = Statement {
-                        source_info: drop_data.0.source_info,
-                        kind: StatementKind::StorageDead(drop_data.0.local),
+                        source_info: drop_node.data.source_info,
+                        kind: StatementKind::StorageDead(drop_node.data.local),
                     };
                     cfg.push(block, stmt);
-                    let target = blocks[drop_data.1].unwrap();
+                    let target = blocks[drop_node.next].unwrap();
                     if target != block {
                         // Diagnostics don't use this `Span` but debuginfo
                         // might. Since we don't want breakpoints to be placed
                         // here, especially when this is on an unwind path, we
                         // use `DUMMY_SP`.
-                        let source_info = SourceInfo { span: DUMMY_SP, ..drop_data.0.source_info };
+                        let source_info =
+                            SourceInfo { span: DUMMY_SP, ..drop_node.data.source_info };
                         let terminator = TerminatorKind::Goto { target };
                         cfg.terminate(block, source_info, terminator);
                     }
@@ -673,11 +698,12 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             .flat_map(|scope| &scope.drops)
             .fold(ROOT_NODE, |drop_idx, &drop| drops.add_drop(drop, drop_idx));
 
-        drops.add_entry(block, drop_idx);
+        drops.add_entry_point(block, drop_idx);
 
         // `build_drop_trees` doesn't have access to our source_info, so we
         // create a dummy terminator now. `TerminatorKind::UnwindResume` is used
         // because MIR type checking will panic if it hasn't been overwritten.
+        // (See `<ExitScopes as DropTreeBuilder>::link_entry_point`.)
         self.cfg.terminate(block, source_info, TerminatorKind::UnwindResume);
 
         self.cfg.start_new_block().unit()
@@ -708,11 +734,12 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 drop_idx = drops.add_drop(*drop, drop_idx);
             }
         }
-        drops.add_entry(block, drop_idx);
+        drops.add_entry_point(block, drop_idx);
 
         // `build_drop_trees` doesn't have access to our source_info, so we
         // create a dummy terminator now. `TerminatorKind::UnwindResume` is used
         // because MIR type checking will panic if it hasn't been overwritten.
+        // (See `<ExitScopes as DropTreeBuilder>::link_entry_point`.)
         self.cfg.terminate(block, source_info, TerminatorKind::UnwindResume);
     }
 
@@ -1119,7 +1146,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         );
 
         let next_drop = self.diverge_cleanup();
-        self.scopes.unwind_drops.add_entry(start, next_drop);
+        self.scopes.unwind_drops.add_entry_point(start, next_drop);
     }
 
     /// Sets up a path that performs all required cleanup for dropping a
@@ -1153,7 +1180,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             scope.cached_coroutine_drop_block = Some(cached_drop);
         }
 
-        self.scopes.coroutine_drops.add_entry(yield_block, cached_drop);
+        self.scopes.coroutine_drops.add_entry_point(yield_block, cached_drop);
     }
 
     /// Utility function for *non*-scope code to build their own drops
@@ -1274,9 +1301,9 @@ fn build_scope_drops<'tcx>(
                 // `unwind_to` should drop the value that we're about to
                 // schedule. If dropping this value panics, then we continue
                 // with the *next* value on the unwind path.
-                debug_assert_eq!(unwind_drops.drops[unwind_to].0.local, drop_data.local);
-                debug_assert_eq!(unwind_drops.drops[unwind_to].0.kind, drop_data.kind);
-                unwind_to = unwind_drops.drops[unwind_to].1;
+                debug_assert_eq!(unwind_drops.drops[unwind_to].data.local, drop_data.local);
+                debug_assert_eq!(unwind_drops.drops[unwind_to].data.kind, drop_data.kind);
+                unwind_to = unwind_drops.drops[unwind_to].next;
 
                 // If the operand has been moved, and we are not on an unwind
                 // path, then don't generate the drop. (We only take this into
@@ -1286,7 +1313,7 @@ fn build_scope_drops<'tcx>(
                     continue;
                 }
 
-                unwind_drops.add_entry(block, unwind_to);
+                unwind_drops.add_entry_point(block, unwind_to);
 
                 let next = cfg.start_new_block();
                 cfg.terminate(
@@ -1303,9 +1330,9 @@ fn build_scope_drops<'tcx>(
             }
             DropKind::Storage => {
                 if storage_dead_on_unwind {
-                    debug_assert_eq!(unwind_drops.drops[unwind_to].0.local, drop_data.local);
-                    debug_assert_eq!(unwind_drops.drops[unwind_to].0.kind, drop_data.kind);
-                    unwind_to = unwind_drops.drops[unwind_to].1;
+                    debug_assert_eq!(unwind_drops.drops[unwind_to].data.local, drop_data.local);
+                    debug_assert_eq!(unwind_drops.drops[unwind_to].data.kind, drop_data.kind);
+                    unwind_to = unwind_drops.drops[unwind_to].next;
                 }
                 // Only temps and vars need their storage dead.
                 assert!(local.index() > arg_count);
@@ -1335,30 +1362,31 @@ impl<'a, 'tcx: 'a> Builder<'a, 'tcx> {
         let is_coroutine = self.coroutine.is_some();
 
         // Link the exit drop tree to unwind drop tree.
-        if drops.drops.iter().any(|(drop, _)| drop.kind == DropKind::Value) {
+        if drops.drops.iter().any(|drop_node| drop_node.data.kind == DropKind::Value) {
             let unwind_target = self.diverge_cleanup_target(else_scope, span);
             let mut unwind_indices = IndexVec::from_elem_n(unwind_target, 1);
-            for (drop_idx, drop_data) in drops.drops.iter_enumerated().skip(1) {
-                match drop_data.0.kind {
+            for (drop_idx, drop_node) in drops.drops.iter_enumerated().skip(1) {
+                match drop_node.data.kind {
                     DropKind::Storage => {
                         if is_coroutine {
                             let unwind_drop = self
                                 .scopes
                                 .unwind_drops
-                                .add_drop(drop_data.0, unwind_indices[drop_data.1]);
+                                .add_drop(drop_node.data, unwind_indices[drop_node.next]);
                             unwind_indices.push(unwind_drop);
                         } else {
-                            unwind_indices.push(unwind_indices[drop_data.1]);
+                            unwind_indices.push(unwind_indices[drop_node.next]);
                         }
                     }
                     DropKind::Value => {
                         let unwind_drop = self
                             .scopes
                             .unwind_drops
-                            .add_drop(drop_data.0, unwind_indices[drop_data.1]);
-                        self.scopes
-                            .unwind_drops
-                            .add_entry(blocks[drop_idx].unwrap(), unwind_indices[drop_data.1]);
+                            .add_drop(drop_node.data, unwind_indices[drop_node.next]);
+                        self.scopes.unwind_drops.add_entry_point(
+                            blocks[drop_idx].unwrap(),
+                            unwind_indices[drop_node.next],
+                        );
                         unwind_indices.push(unwind_drop);
                     }
                 }
@@ -1408,10 +1436,10 @@ impl<'a, 'tcx: 'a> Builder<'a, 'tcx> {
         // prevent drop elaboration from creating drop flags that would have
         // to be captured by the coroutine. I'm not sure how important this
         // optimization is, but it is here.
-        for (drop_idx, drop_data) in drops.drops.iter_enumerated() {
-            if let DropKind::Value = drop_data.0.kind {
-                debug_assert!(drop_data.1 < drops.drops.next_index());
-                drops.entry_points.push((drop_data.1, blocks[drop_idx].unwrap()));
+        for (drop_idx, drop_node) in drops.drops.iter_enumerated() {
+            if let DropKind::Value = drop_node.data.kind {
+                debug_assert!(drop_node.next < drops.drops.next_index());
+                drops.entry_points.push((drop_node.next, blocks[drop_idx].unwrap()));
             }
         }
         Self::build_unwind_tree(cfg, drops, fn_span, resume_block);
@@ -1442,8 +1470,16 @@ impl<'tcx> DropTreeBuilder<'tcx> for ExitScopes {
     fn make_block(cfg: &mut CFG<'tcx>) -> BasicBlock {
         cfg.start_new_block()
     }
-    fn add_entry(cfg: &mut CFG<'tcx>, from: BasicBlock, to: BasicBlock) {
-        cfg.block_data_mut(from).terminator_mut().kind = TerminatorKind::Goto { target: to };
+    fn link_entry_point(cfg: &mut CFG<'tcx>, from: BasicBlock, to: BasicBlock) {
+        // There should be an existing terminator with real source info and a
+        // dummy TerminatorKind. Replace it with a proper goto.
+        // (The dummy is added by `break_scope` and `break_for_else`.)
+        let term = cfg.block_data_mut(from).terminator_mut();
+        if let TerminatorKind::UnwindResume = term.kind {
+            term.kind = TerminatorKind::Goto { target: to };
+        } else {
+            span_bug!(term.source_info.span, "unexpected dummy terminator kind: {:?}", term.kind);
+        }
     }
 }
 
@@ -1453,7 +1489,7 @@ impl<'tcx> DropTreeBuilder<'tcx> for CoroutineDrop {
     fn make_block(cfg: &mut CFG<'tcx>) -> BasicBlock {
         cfg.start_new_block()
     }
-    fn add_entry(cfg: &mut CFG<'tcx>, from: BasicBlock, to: BasicBlock) {
+    fn link_entry_point(cfg: &mut CFG<'tcx>, from: BasicBlock, to: BasicBlock) {
         let term = cfg.block_data_mut(from).terminator_mut();
         if let TerminatorKind::Yield { ref mut drop, .. } = term.kind {
             *drop = Some(to);
@@ -1473,7 +1509,7 @@ impl<'tcx> DropTreeBuilder<'tcx> for Unwind {
     fn make_block(cfg: &mut CFG<'tcx>) -> BasicBlock {
         cfg.start_new_cleanup_block()
     }
-    fn add_entry(cfg: &mut CFG<'tcx>, from: BasicBlock, to: BasicBlock) {
+    fn link_entry_point(cfg: &mut CFG<'tcx>, from: BasicBlock, to: BasicBlock) {
         let term = &mut cfg.block_data_mut(from).terminator_mut();
         match &mut term.kind {
             TerminatorKind::Drop { unwind, .. } => {

compiler/rustc_parse/src/parser/path.rs

@@ -1,6 +1,7 @@
 use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign};
 use super::{Parser, Restrictions, TokenType};
 use crate::errors::PathSingleColon;
+use crate::parser::{CommaRecoveryMode, RecoverColon, RecoverComma};
 use crate::{errors, maybe_whole};
 use ast::token::IdentIsRaw;
 use rustc_ast::ptr::P;
@@ -10,7 +11,7 @@ use rustc_ast::{
     AssocConstraintKind, BlockCheckMode, GenericArg, GenericArgs, Generics, ParenthesizedArgs,
     Path, PathSegment, QSelf,
 };
-use rustc_errors::{Applicability, PResult};
+use rustc_errors::{Applicability, Diag, PResult};
 use rustc_span::symbol::{kw, sym, Ident};
 use rustc_span::{BytePos, Span};
 use std::mem;
@@ -373,7 +374,38 @@ impl<'a> Parser<'a> {
                     .into()
                 } else {
                     // `(T, U) -> R`
-                    let (inputs, _) = self.parse_paren_comma_seq(|p| p.parse_ty())?;
+
+                    let prev_token_before_parsing = self.prev_token.clone();
+                    let token_before_parsing = self.token.clone();
+                    let mut snapshot = None;
+                    if self.may_recover()
+                        && prev_token_before_parsing.kind == token::ModSep
+                        && (style == PathStyle::Expr && self.token.can_begin_expr()
+                            || style == PathStyle::Pat && self.token.can_begin_pattern())
+                    {
+                        snapshot = Some(self.create_snapshot_for_diagnostic());
+                    }
+
+                    let (inputs, _) = match self.parse_paren_comma_seq(|p| p.parse_ty()) {
+                        Ok(output) => output,
+                        Err(mut error) if prev_token_before_parsing.kind == token::ModSep => {
+                            error.span_label(
+                                prev_token_before_parsing.span.to(token_before_parsing.span),
+                                "while parsing this parenthesized list of type arguments starting here",
+                            );
+
+                            if let Some(mut snapshot) = snapshot {
+                                snapshot.recover_fn_call_leading_path_sep(
+                                    style,
+                                    prev_token_before_parsing,
+                                    &mut error,
+                                )
+                            }
+
+                            return Err(error);
+                        }
+                        Err(error) => return Err(error),
+                    };
                     let inputs_span = lo.to(self.prev_token.span);
                     let output =
                         self.parse_ret_ty(AllowPlus::No, RecoverQPath::No, RecoverReturnSign::No)?;
@@ -399,6 +431,56 @@ impl<'a> Parser<'a> {
         }
     }
 
+    /// Recover `$path::(...)` as `$path(...)`.
+    ///
+    /// ```ignore (diagnostics)
+    /// foo::(420, "bar")
+    ///    ^^ remove extra separator to make the function call
+    /// // or
+    /// match x {
+    ///    Foo::(420, "bar") => { ... },
+    ///       ^^ remove extra separator to turn this into tuple struct pattern
+    ///    _ => { ... },
+    /// }
+    /// ```
+    fn recover_fn_call_leading_path_sep(
+        &mut self,
+        style: PathStyle,
+        prev_token_before_parsing: Token,
+        error: &mut Diag<'_>,
+    ) {
+        if ((style == PathStyle::Expr && self.parse_paren_comma_seq(|p| p.parse_expr()).is_ok())
+            || (style == PathStyle::Pat
+                && self
+                    .parse_paren_comma_seq(|p| {
+                        p.parse_pat_allow_top_alt(
+                            None,
+                            RecoverComma::No,
+                            RecoverColon::No,
+                            CommaRecoveryMode::LikelyTuple,
+                        )
+                    })
+                    .is_ok()))
+            && !matches!(self.token.kind, token::ModSep | token::RArrow)
+        {
+            error.span_suggestion_verbose(
+                prev_token_before_parsing.span,
+                format!(
+                    "consider removing the `::` here to {}",
+                    match style {
+                        PathStyle::Expr => "call the expression",
+                        PathStyle::Pat => "turn this into a tuple struct pattern",
+                        _ => {
+                            return;
+                        }
+                    }
+                ),
+                "",
+                Applicability::MaybeIncorrect,
+            );
+        }
+    }
+
     /// Parses generic args (within a path segment) with recovery for extra leading angle brackets.
     /// For the purposes of understanding the parsing logic of generic arguments, this function
     /// can be thought of being the same as just calling `self.parse_angle_args()` if the source

compiler/rustc_session/src/config.rs

@@ -8,7 +8,7 @@ pub use crate::options::*;
 use crate::errors::FileWriteFail;
 use crate::search_paths::SearchPath;
 use crate::utils::{CanonicalizedPath, NativeLib, NativeLibKind};
-use crate::{lint, HashStableContext};
+use crate::{filesearch, lint, HashStableContext};
 use crate::{EarlyDiagCtxt, Session};
 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap, FxIndexSet};
 use rustc_data_structures::stable_hasher::{StableOrd, ToStableHashKey};
@@ -1564,7 +1564,7 @@ pub fn build_configuration(sess: &Session, mut user_cfg: Cfg) -> Cfg {
     user_cfg
 }
 
-pub(super) fn build_target_config(
+pub fn build_target_config(
     early_dcx: &EarlyDiagCtxt,
     opts: &Options,
     target_override: Option<Target>,
@@ -2863,16 +2863,8 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
 
     let logical_env = parse_logical_env(early_dcx, matches);
 
-    // Try to find a directory containing the Rust `src`, for more details see
-    // the doc comment on the `real_rust_source_base_dir` field.
-    let tmp_buf;
-    let sysroot = match &sysroot_opt {
-        Some(s) => s,
-        None => {
-            tmp_buf = crate::filesearch::get_or_default_sysroot().expect("Failed finding sysroot");
-            &tmp_buf
-        }
-    };
+    let sysroot = filesearch::materialize_sysroot(sysroot_opt);
+
     let real_rust_source_base_dir = {
         // This is the location used by the `rust-src` `rustup` component.
         let mut candidate = sysroot.join("lib/rustlib/src/rust");
@@ -2916,7 +2908,7 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
         describe_lints,
         output_types,
         search_paths,
-        maybe_sysroot: sysroot_opt,
+        maybe_sysroot: Some(sysroot),
         target_triple,
         test,
         incremental,

compiler/rustc_session/src/filesearch.rs

@@ -193,6 +193,12 @@ pub fn sysroot_candidates() -> SmallVec<[PathBuf; 2]> {
     return sysroot_candidates;
 }
 
+/// Returns the provided sysroot or calls [`get_or_default_sysroot`] if it's none.
+/// Panics if [`get_or_default_sysroot`]  returns an error.
+pub fn materialize_sysroot(maybe_sysroot: Option<PathBuf>) -> PathBuf {
+    maybe_sysroot.unwrap_or_else(|| get_or_default_sysroot().expect("Failed finding sysroot"))
+}
+
 /// This function checks if sysroot is found using env::args().next(), and if it
 /// is not found, finds sysroot from current rustc_driver dll.
 pub fn get_or_default_sysroot() -> Result<PathBuf, String> {

compiler/rustc_session/src/options.rs

@@ -1772,7 +1772,7 @@ options! {
         "disable the 'leak check' for subtyping; unsound, but useful for tests"),
     no_link: bool = (false, parse_no_flag, [TRACKED],
         "compile without linking"),
-    no_parallel_llvm: bool = (false, parse_no_flag, [UNTRACKED],
+    no_parallel_backend: bool = (false, parse_no_flag, [UNTRACKED],
         "run LLVM in non-parallel mode (while keeping codegen-units and ThinLTO)"),
     no_profiler_runtime: bool = (false, parse_no_flag, [TRACKED],
         "prevent automatic injection of the profiler_builtins crate"),

compiler/rustc_session/src/session.rs

@@ -1016,7 +1016,8 @@ pub fn build_session(
     fluent_resources: Vec<&'static str>,
     driver_lint_caps: FxHashMap<lint::LintId, lint::Level>,
     file_loader: Option<Box<dyn FileLoader + Send + Sync + 'static>>,
-    target_override: Option<Target>,
+    target_cfg: Target,
+    sysroot: PathBuf,
     cfg_version: &'static str,
     ice_file: Option<PathBuf>,
     using_internal_features: Arc<AtomicBool>,
@@ -1033,12 +1034,6 @@ pub fn build_session(
     let cap_lints_allow = sopts.lint_cap.is_some_and(|cap| cap == lint::Allow);
     let can_emit_warnings = !(warnings_allow || cap_lints_allow);
 
-    let sysroot = match &sopts.maybe_sysroot {
-        Some(sysroot) => sysroot.clone(),
-        None => filesearch::get_or_default_sysroot().expect("Failed finding sysroot"),
-    };
-
-    let target_cfg = config::build_target_config(&early_dcx, &sopts, target_override, &sysroot);
     let host_triple = TargetTriple::from_triple(config::host_triple());
     let (host, target_warnings) = Target::search(&host_triple, &sysroot).unwrap_or_else(|e| {
         early_dcx.early_fatal(format!("Error loading host specification: {e}"))

compiler/rustc_target/src/spec/mod.rs

@@ -123,6 +123,8 @@ pub enum LinkerFlavor {
     Bpf,
     /// Linker tool for Nvidia PTX.
     Ptx,
+    /// LLVM bitcode linker that can be used as a `self-contained` linker
+    Llbc,
 }
 
 /// Linker flavors available externally through command line (`-Clinker-flavor`)
@@ -141,6 +143,7 @@ pub enum LinkerFlavorCli {
     EmCc,
     Bpf,
     Ptx,
+    Llbc,
 
     // Legacy stable values
     Gcc,
@@ -160,6 +163,7 @@ impl LinkerFlavorCli {
             | LinkerFlavorCli::Msvc(Lld::Yes)
             | LinkerFlavorCli::EmCc
             | LinkerFlavorCli::Bpf
+            | LinkerFlavorCli::Llbc
             | LinkerFlavorCli::Ptx => true,
             LinkerFlavorCli::Gcc
             | LinkerFlavorCli::Ld
@@ -219,6 +223,7 @@ impl LinkerFlavor {
             LinkerFlavorCli::Msvc(lld) => LinkerFlavor::Msvc(lld),
             LinkerFlavorCli::EmCc => LinkerFlavor::EmCc,
             LinkerFlavorCli::Bpf => LinkerFlavor::Bpf,
+            LinkerFlavorCli::Llbc => LinkerFlavor::Llbc,
             LinkerFlavorCli::Ptx => LinkerFlavor::Ptx,
 
             // Below: legacy stable values
@@ -258,6 +263,7 @@ impl LinkerFlavor {
             LinkerFlavor::Msvc(..) => LinkerFlavorCli::Msvc(Lld::No),
             LinkerFlavor::EmCc => LinkerFlavorCli::Em,
             LinkerFlavor::Bpf => LinkerFlavorCli::Bpf,
+            LinkerFlavor::Llbc => LinkerFlavorCli::Llbc,
             LinkerFlavor::Ptx => LinkerFlavorCli::Ptx,
         }
     }
@@ -272,6 +278,7 @@ impl LinkerFlavor {
             LinkerFlavor::Msvc(lld) => LinkerFlavorCli::Msvc(lld),
             LinkerFlavor::EmCc => LinkerFlavorCli::EmCc,
             LinkerFlavor::Bpf => LinkerFlavorCli::Bpf,
+            LinkerFlavor::Llbc => LinkerFlavorCli::Llbc,
             LinkerFlavor::Ptx => LinkerFlavorCli::Ptx,
         }
     }
@@ -286,6 +293,7 @@ impl LinkerFlavor {
             LinkerFlavorCli::Msvc(lld) => (Some(Cc::No), Some(lld)),
             LinkerFlavorCli::EmCc => (Some(Cc::Yes), Some(Lld::Yes)),
             LinkerFlavorCli::Bpf | LinkerFlavorCli::Ptx => (None, None),
+            LinkerFlavorCli::Llbc => (None, None),
 
             // Below: legacy stable values
             LinkerFlavorCli::Gcc => (Some(Cc::Yes), None),
@@ -340,7 +348,7 @@ impl LinkerFlavor {
             LinkerFlavor::WasmLld(cc) => LinkerFlavor::WasmLld(cc_hint.unwrap_or(cc)),
             LinkerFlavor::Unix(cc) => LinkerFlavor::Unix(cc_hint.unwrap_or(cc)),
             LinkerFlavor::Msvc(lld) => LinkerFlavor::Msvc(lld_hint.unwrap_or(lld)),
-            LinkerFlavor::EmCc | LinkerFlavor::Bpf | LinkerFlavor::Ptx => self,
+            LinkerFlavor::EmCc | LinkerFlavor::Bpf | LinkerFlavor::Llbc | LinkerFlavor::Ptx => self,
         }
     }
 
@@ -355,8 +363,8 @@ impl LinkerFlavor {
     pub fn check_compatibility(self, cli: LinkerFlavorCli) -> Option<String> {
         let compatible = |cli| {
             // The CLI flavor should be compatible with the target if:
-            // 1. they are counterparts: they have the same principal flavor.
             match (self, cli) {
+                // 1. they are counterparts: they have the same principal flavor.
                 (LinkerFlavor::Gnu(..), LinkerFlavorCli::Gnu(..))
                 | (LinkerFlavor::Darwin(..), LinkerFlavorCli::Darwin(..))
                 | (LinkerFlavor::WasmLld(..), LinkerFlavorCli::WasmLld(..))
@@ -364,11 +372,14 @@ impl LinkerFlavor {
                 | (LinkerFlavor::Msvc(..), LinkerFlavorCli::Msvc(..))
                 | (LinkerFlavor::EmCc, LinkerFlavorCli::EmCc)
                 | (LinkerFlavor::Bpf, LinkerFlavorCli::Bpf)
+                | (LinkerFlavor::Llbc, LinkerFlavorCli::Llbc)
                 | (LinkerFlavor::Ptx, LinkerFlavorCli::Ptx) => return true,
+                // 2. The linker flavor is independent of target and compatible
+                (LinkerFlavor::Ptx, LinkerFlavorCli::Llbc) => return true,
                 _ => {}
             }
 
-            // 2. or, the flavor is legacy and survives this roundtrip.
+            // 3. or, the flavor is legacy and survives this roundtrip.
             cli == self.with_cli_hints(cli).to_cli()
         };
         (!compatible(cli)).then(|| {
@@ -387,6 +398,7 @@ impl LinkerFlavor {
             | LinkerFlavor::Unix(..)
             | LinkerFlavor::EmCc
             | LinkerFlavor::Bpf
+            | LinkerFlavor::Llbc
             | LinkerFlavor::Ptx => LldFlavor::Ld,
             LinkerFlavor::Darwin(..) => LldFlavor::Ld64,
             LinkerFlavor::WasmLld(..) => LldFlavor::Wasm,
@@ -412,6 +424,7 @@ impl LinkerFlavor {
             | LinkerFlavor::Msvc(_)
             | LinkerFlavor::Unix(_)
             | LinkerFlavor::Bpf
+            | LinkerFlavor::Llbc
             | LinkerFlavor::Ptx => false,
         }
     }
@@ -431,6 +444,7 @@ impl LinkerFlavor {
             | LinkerFlavor::Msvc(_)
             | LinkerFlavor::Unix(_)
             | LinkerFlavor::Bpf
+            | LinkerFlavor::Llbc
             | LinkerFlavor::Ptx => false,
         }
     }
@@ -480,6 +494,7 @@ linker_flavor_cli_impls! {
     (LinkerFlavorCli::Msvc(Lld::No)) "msvc"
     (LinkerFlavorCli::EmCc) "em-cc"
     (LinkerFlavorCli::Bpf) "bpf"
+    (LinkerFlavorCli::Llbc) "llbc"
     (LinkerFlavorCli::Ptx) "ptx"
 
     // Legacy stable flavors
@@ -2070,6 +2085,14 @@ pub struct TargetOptions {
     /// Default number of codegen units to use in debug mode
     pub default_codegen_units: Option<u64>,
 
+    /// Default codegen backend used for this target. Defaults to `None`.
+    ///
+    /// If `None`, then `CFG_DEFAULT_CODEGEN_BACKEND` environmental variable captured when
+    /// compiling `rustc` will be used instead (or llvm if it is not set).
+    ///
+    /// N.B. when *using* the compiler, backend can always be overriden with `-Zcodegen-backend`.
+    pub default_codegen_backend: Option<StaticCow<str>>,
+
     /// Whether to generate trap instructions in places where optimization would
     /// otherwise produce control flow that falls through into unrelated memory.
     pub trap_unreachable: bool,
@@ -2220,6 +2243,7 @@ fn add_link_args_iter(
         | LinkerFlavor::Unix(..)
         | LinkerFlavor::EmCc
         | LinkerFlavor::Bpf
+        | LinkerFlavor::Llbc
         | LinkerFlavor::Ptx => {}
     }
 }
@@ -2376,6 +2400,7 @@ impl Default for TargetOptions {
             stack_probes: StackProbeType::None,
             min_global_align: None,
             default_codegen_units: None,
+            default_codegen_backend: None,
             trap_unreachable: true,
             requires_lto: false,
             singlethread: false,

compiler/rustc_target/src/spec/targets/nvptx64_nvidia_cuda.rs

@@ -1,3 +1,4 @@
+use crate::spec::LinkSelfContainedDefault;
 use crate::spec::{LinkerFlavor, MergeFunctions, PanicStrategy, Target, TargetOptions};
 
 pub fn target() -> Target {
@@ -52,6 +53,9 @@ pub fn target() -> Target {
             // The LLVM backend does not support stack canaries for this target
             supports_stack_protector: false,
 
+            // Support using `self-contained` linkers like the llvm-bitcode-linker
+            link_self_contained: LinkSelfContainedDefault::True,
+
             ..Default::default()
         },
     }

compiler/rustc_target/src/spec/tests/tests_impl.rs

@@ -56,7 +56,10 @@ impl Target {
                     LinkerFlavor::Msvc(..) => {
                         assert_matches!(flavor, LinkerFlavor::Msvc(..))
                     }
-                    LinkerFlavor::EmCc | LinkerFlavor::Bpf | LinkerFlavor::Ptx => {
+                    LinkerFlavor::EmCc
+                    | LinkerFlavor::Bpf
+                    | LinkerFlavor::Ptx
+                    | LinkerFlavor::Llbc => {
                         assert_eq!(flavor, self.linker_flavor)
                     }
                 }

config.example.toml

@@ -679,6 +679,10 @@
 # sysroot.
 #llvm-tools = true
 
+# Indicates whether the `self-contained` llvm-bitcode-linker, will be made available
+# in the sysroot
+#llvm-bitcode-linker = false
+
 # Whether to deny warnings in crates
 #deny-warnings = true
 

library/panic_unwind/src/gcc.rs

@@ -62,7 +62,7 @@ pub unsafe fn panic(data: Box<dyn Any + Send>) -> u32 {
     let exception = Box::new(Exception {
         _uwe: uw::_Unwind_Exception {
             exception_class: rust_exception_class(),
-            exception_cleanup,
+            exception_cleanup: Some(exception_cleanup),
             private: [core::ptr::null(); uw::unwinder_private_data_size],
         },
         canary: &CANARY,

library/panic_unwind/src/lib.rs

@@ -53,12 +53,12 @@ cfg_if::cfg_if! {
         target_os = "solid_asp3",
         all(target_family = "unix", not(target_os = "espidf")),
         all(target_vendor = "fortanix", target_env = "sgx"),
+        target_family = "wasm",
     ))] {
         #[path = "gcc.rs"]
         mod real_imp;
     } else {
         // Targets that don't support unwinding.
-        // - family=wasm
         // - os=none ("bare metal" targets)
         // - os=uefi
         // - os=espidf

library/std/src/sys/personality/mod.rs

@@ -16,11 +16,12 @@ mod dwarf;
 cfg_if::cfg_if! {
     if #[cfg(target_os = "emscripten")] {
         mod emcc;
-    } else if #[cfg(target_env = "msvc")] {
+    } else if #[cfg(any(target_env = "msvc", target_family = "wasm"))] {
         // This is required by the compiler to exist (e.g., it's a lang item),
         // but it's never actually called by the compiler because
-        // _CxxFrameHandler3 is the personality function that is always used.
-        // Hence this is just an aborting stub.
+        // __CxxFrameHandler3 (msvc) / __gxx_wasm_personality_v0 (wasm) is the
+        // personality function that is always used.  Hence this is just an
+        // aborting stub.
         #[lang = "eh_personality"]
         fn rust_eh_personality() {
             core::intrinsics::abort()
@@ -36,7 +37,6 @@ cfg_if::cfg_if! {
         mod gcc;
     } else {
         // Targets that don't support unwinding.
-        // - family=wasm
         // - os=none ("bare metal" targets)
         // - os=uefi
         // - os=espidf

library/unwind/src/lib.rs

@@ -6,6 +6,10 @@
 #![cfg_attr(bootstrap, feature(cfg_target_abi))]
 #![feature(strict_provenance)]
 #![cfg_attr(not(target_env = "msvc"), feature(libc))]
+#![cfg_attr(
+    all(target_family = "wasm", not(target_os = "emscripten")),
+    feature(link_llvm_intrinsics)
+)]
 #![allow(internal_features)]
 
 cfg_if::cfg_if! {
@@ -29,9 +33,11 @@ cfg_if::cfg_if! {
     } else if #[cfg(target_os = "xous")] {
         mod unwinding;
         pub use unwinding::*;
+    } else if #[cfg(target_family = "wasm")] {
+        mod wasm;
+        pub use wasm::*;
     } else {
         // no unwinder on the system!
-        // - wasm32 (not emscripten, which is "unix" family)
         // - os=none ("bare metal" targets)
         // - os=hermit
         // - os=uefi

library/unwind/src/libunwind.rs

@@ -91,7 +91,7 @@ pub struct _Unwind_Exception {
 pub enum _Unwind_Context {}
 
 pub type _Unwind_Exception_Cleanup_Fn =
-    extern "C" fn(unwind_code: _Unwind_Reason_Code, exception: *mut _Unwind_Exception);
+    Option<extern "C" fn(unwind_code: _Unwind_Reason_Code, exception: *mut _Unwind_Exception)>;
 
 // FIXME: The `#[link]` attributes on `extern "C"` block marks those symbols declared in
 // the block are reexported in dylib build of std. This is needed when build rustc with

library/unwind/src/unwinding.rs

@@ -46,7 +46,7 @@ pub const unwinder_private_data_size: usize = core::mem::size_of::<UnwindExcepti
     - core::mem::size_of::<_Unwind_Exception_Cleanup_Fn>();
 
 pub type _Unwind_Exception_Cleanup_Fn =
-    extern "C" fn(unwind_code: _Unwind_Reason_Code, exception: *mut _Unwind_Exception);
+    Option<extern "C" fn(unwind_code: _Unwind_Reason_Code, exception: *mut _Unwind_Exception)>;
 
 #[repr(C)]
 pub struct _Unwind_Exception {

library/unwind/src/wasm.rs

@@ -0,0 +1,65 @@
+//! A shim for libunwind implemented in terms of the native wasm `throw` instruction.
+
+#![allow(nonstandard_style)]
+
+#[repr(C)]
+#[derive(Debug, Copy, Clone, PartialEq)]
+pub enum _Unwind_Reason_Code {
+    _URC_NO_REASON = 0,
+    _URC_FOREIGN_EXCEPTION_CAUGHT = 1,
+    _URC_FATAL_PHASE2_ERROR = 2,
+    _URC_FATAL_PHASE1_ERROR = 3,
+    _URC_NORMAL_STOP = 4,
+    _URC_END_OF_STACK = 5,
+    _URC_HANDLER_FOUND = 6,
+    _URC_INSTALL_CONTEXT = 7,
+    _URC_CONTINUE_UNWIND = 8,
+    _URC_FAILURE = 9, // used only by ARM EHABI
+}
+pub use _Unwind_Reason_Code::*;
+
+pub type _Unwind_Exception_Class = u64;
+pub type _Unwind_Word = *const u8;
+
+pub const unwinder_private_data_size: usize = 2;
+
+#[repr(C)]
+pub struct _Unwind_Exception {
+    pub exception_class: _Unwind_Exception_Class,
+    pub exception_cleanup: _Unwind_Exception_Cleanup_Fn,
+    pub private: [_Unwind_Word; unwinder_private_data_size],
+}
+
+pub type _Unwind_Exception_Cleanup_Fn =
+    Option<extern "C" fn(unwind_code: _Unwind_Reason_Code, exception: *mut _Unwind_Exception)>;
+
+pub unsafe fn _Unwind_DeleteException(exception: *mut _Unwind_Exception) {
+    if let Some(exception_cleanup) = unsafe { (*exception).exception_cleanup } {
+        exception_cleanup(_URC_FOREIGN_EXCEPTION_CAUGHT, exception);
+    }
+}
+
+pub unsafe fn _Unwind_RaiseException(exception: *mut _Unwind_Exception) -> _Unwind_Reason_Code {
+    #[cfg(panic = "unwind")]
+    extern "C" {
+        /// LLVM lowers this intrinsic to the `throw` instruction.
+        // FIXME(coolreader18): move to stdarch
+        #[link_name = "llvm.wasm.throw"]
+        fn wasm_throw(tag: i32, ptr: *mut u8) -> !;
+    }
+
+    // The wasm `throw` instruction takes a "tag", which differentiates certain
+    // types of exceptions from others. LLVM currently just identifies these
+    // via integers, with 0 corresponding to C++ exceptions and 1 to C setjmp()/longjmp().
+    // Ideally, we'd be able to choose something unique for Rust, but for now,
+    // we pretend to be C++ and implement the Itanium exception-handling ABI.
+    cfg_if::cfg_if! {
+        // for now, unless we're -Zbuild-std with panic=unwind, never codegen a throw.
+        if #[cfg(panic = "unwind")] {
+            wasm_throw(0, exception.cast())
+        } else {
+            let _ = exception;
+            core::arch::wasm32::unreachable()
+        }
+    }
+}

src/bootstrap/README.md

@@ -1,7 +1,7 @@
 # rustbuild - Bootstrapping Rust
 
-This README is aimed at helping to explain how Rust is bootstrapped and in general,
-some of the technical details of the build system.
+This README is aimed at helping to explain how Rust is bootstrapped,
+and some of the technical details of the build system.
 
 Note that this README only covers internal information, not how to use the tool.
 Please check [bootstrapping dev guide][bootstrapping-dev-guide] for further information.
@@ -10,12 +10,12 @@ Please check [bootstrapping dev guide][bootstrapping-dev-guide] for further info
 
 ## Introduction
 
-The build system defers most of the complicated logic managing invocations
+The build system defers most of the complicated logic of managing invocations
 of rustc and rustdoc to Cargo itself. However, moving through various stages
 and copying artifacts is still necessary for it to do. Each time rustbuild
 is invoked, it will iterate through the list of predefined steps and execute
 each serially in turn if it matches the paths passed or is a default rule.
-For each step rustbuild relies on the step internally being incremental and
+For each step, rustbuild relies on the step internally being incremental and
 parallel. Note, though, that the `-j` parameter to rustbuild gets forwarded
 to appropriate test harnesses and such.
 
@@ -24,7 +24,7 @@ to appropriate test harnesses and such.
 The rustbuild build system goes through a few phases to actually build the
 compiler. What actually happens when you invoke rustbuild is:
 
-1. The entry point script(`x` for unix like systems, `x.ps1` for windows systems,
+1. The entry point script (`x` for unix like systems, `x.ps1` for windows systems,
    `x.py` cross-platform) is run. This script is responsible for downloading the stage0
    compiler/Cargo binaries, and it then compiles the build system itself (this folder).
    Finally, it then invokes the actual `bootstrap` binary build system.
@@ -107,12 +107,13 @@ build/
 
     # Location where the stage0 Cargo and Rust compiler are unpacked. This
     # directory is purely an extracted and overlaid tarball of these two (done
-    # by the bootstrap python script). In theory, the build system does not
+    # by the bootstrap Python script). In theory, the build system does not
     # modify anything under this directory afterwards.
     stage0/
 
     # These to-build directories are the cargo output directories for builds of
-    # the standard library and compiler, respectively. Internally, these may also
+    # the standard library, the test system, the compiler, and various tools,
+    # respectively. Internally, these may also
     # have other target directories, which represent artifacts being compiled
     # from the host to the specified target.
     #
@@ -169,17 +170,17 @@ read by the other.
 
 Some general areas that you may be interested in modifying are:
 
-* Adding a new build tool? Take a look at `bootstrap/tool.rs` for examples of
-  other tools.
+* Adding a new build tool? Take a look at `bootstrap/src/core/build_steps/tool.rs`
+  for examples of other tools.
 * Adding a new compiler crate? Look no further! Adding crates can be done by
-  adding a new directory with `Cargo.toml` followed by configuring all
+  adding a new directory with `Cargo.toml`, followed by configuring all
   `Cargo.toml` files accordingly.
 * Adding a new dependency from crates.io? This should just work inside the
   compiler artifacts stage (everything other than libtest and libstd).
-* Adding a new configuration option? You'll want to modify `bootstrap/flags.rs`
-  for command line flags and then `bootstrap/config.rs` to copy the flags to the
+* Adding a new configuration option? You'll want to modify `bootstrap/src/core/config/flags.rs`
+  for command line flags and then `bootstrap/src/core/config/config.rs` to copy the flags to the
   `Config` struct.
-* Adding a sanity check? Take a look at `bootstrap/sanity.rs`.
+* Adding a sanity check? Take a look at `bootstrap/src/core/sanity.rs`.
 
 If you make a major change on bootstrap configuration, please remember to:
 

src/bootstrap/configure.py

@@ -54,6 +54,7 @@ o("cargo-native-static", "build.cargo-native-static", "static native libraries i
 o("profiler", "build.profiler", "build the profiler runtime")
 o("full-tools", None, "enable all tools")
 o("lld", "rust.lld", "build lld")
+o("llvm-bitcode-linker", "rust.llvm-bitcode-linker", "build llvm bitcode linker")
 o("clang", "llvm.clang", "build clang")
 o("use-libcxx", "llvm.use-libcxx", "build LLVM with libc++")
 o("control-flow-guard", "rust.control-flow-guard", "Enable Control Flow Guard")
@@ -366,6 +367,7 @@ def apply_args(known_args, option_checking, config):
             set('rust.codegen-backends', ['llvm'], config)
             set('rust.lld', True, config)
             set('rust.llvm-tools', True, config)
+            set('rust.llvm-bitcode-linker', True, config)
             set('build.extended', True, config)
         elif option.name in ['option-checking', 'verbose-configure']:
             # this was handled above

src/bootstrap/defaults/config.compiler.toml

@@ -17,6 +17,8 @@ lto = "off"
 # Forces frame pointers to be used with `-Cforce-frame-pointers`.
 # This can be helpful for profiling at a small performance cost.
 frame-pointers = true
+# Build the llvm-bitcode-linker as it is required for running nvptx tests
+llvm-bitcode-linker = true
 
 [llvm]
 # Having this set to true disrupts compiler development workflows for people who use `llvm.download-ci-llvm = true`

src/bootstrap/defaults/config.dist.toml

@@ -16,6 +16,8 @@ download-ci-llvm = false
 # Make sure they don't get set when installing from source.
 channel = "nightly"
 download-rustc = false
+# Build the llvm-bitcode-linker as it is required for running nvptx tests
+llvm-bitcode-linker = true
 
 [dist]
 # Use better compression when preparing tarballs.

src/bootstrap/defaults/config.library.toml

@@ -10,6 +10,8 @@ bench-stage = 0
 incremental = true
 # Make the compiler and standard library faster to build, at the expense of a ~20% runtime slowdown.
 lto = "off"
+# Build the llvm-bitcode-linker as it is required for running nvptx tests
+llvm-bitcode-linker = true
 
 [llvm]
 # Will download LLVM from CI if available on your platform.

src/bootstrap/defaults/config.tools.toml

@@ -12,6 +12,8 @@ incremental = true
 # Using these defaults will download the stage2 compiler (see `download-rustc`
 # setting) and the stage2 toolchain should therefore be used for these defaults.
 download-rustc = "if-unchanged"
+# Build the llvm-bitcode-linker as it is required for running nvptx tests
+llvm-bitcode-linker = true
 
 [build]
 # Document with the in-tree rustdoc by default, since `download-rustc` makes it quick to compile.

src/bootstrap/src/core/build_steps/compile.rs

@@ -1843,6 +1843,16 @@ impl Step for Assemble {
             }
         }
 
+        if builder.config.llvm_bitcode_linker_enabled {
+            let src_path = builder.ensure(crate::core::build_steps::tool::LlvmBitcodeLinker {
+                compiler: build_compiler,
+                target: target_compiler.host,
+                extra_features: vec![],
+            });
+            let tool_exe = exe("llvm-bitcode-linker", target_compiler.host);
+            builder.copy(&src_path, &libdir_bin.join(&tool_exe));
+        }
+
         // Ensure that `libLLVM.so` ends up in the newly build compiler directory,
         // so that it can be found when the newly built `rustc` is run.
         dist::maybe_install_llvm_runtime(builder, target_compiler.host, &sysroot);

src/bootstrap/src/core/build_steps/tool.rs

@@ -795,6 +795,7 @@ tool_extended!((self, builder),
     Rls, "src/tools/rls", "rls", stable=true, tool_std=true;
     RustDemangler, "src/tools/rust-demangler", "rust-demangler", stable=false, tool_std=true;
     Rustfmt, "src/tools/rustfmt", "rustfmt", stable=true, add_bins_to_sysroot = ["rustfmt", "cargo-fmt"];
+    LlvmBitcodeLinker, "src/tools/llvm-bitcode-linker", "llvm-bitcode-linker", stable=false, add_bins_to_sysroot = ["llvm-bitcode-linker"];
 );
 
 impl<'a> Builder<'a> {

src/bootstrap/src/core/builder.rs

@@ -763,6 +763,7 @@ impl<'a> Builder<'a> {
                 tool::RustdocGUITest,
                 tool::OptimizedDist,
                 tool::CoverageDump,
+                tool::LlvmBitcodeLinker
             ),
             Kind::Check | Kind::Clippy | Kind::Fix => describe!(
                 check::Std,

src/bootstrap/src/core/config/config.rs

@@ -236,6 +236,7 @@ pub struct Config {
     pub lld_mode: LldMode,
     pub lld_enabled: bool,
     pub llvm_tools_enabled: bool,
+    pub llvm_bitcode_linker_enabled: bool,
 
     pub llvm_cflags: Option<String>,
     pub llvm_cxxflags: Option<String>,
@@ -1099,6 +1100,7 @@ define_config! {
         dist_src: Option<bool> = "dist-src",
         save_toolstates: Option<String> = "save-toolstates",
         codegen_backends: Option<Vec<String>> = "codegen-backends",
+        llvm_bitcode_linker: Option<bool> = "llvm-bitcode-linker",
         lld: Option<bool> = "lld",
         lld_mode: Option<LldMode> = "use-lld",
         llvm_tools: Option<bool> = "llvm-tools",
@@ -1571,6 +1573,7 @@ impl Config {
                 codegen_backends,
                 lld,
                 llvm_tools,
+                llvm_bitcode_linker,
                 deny_warnings,
                 backtrace_on_ice,
                 verify_llvm_ir,
@@ -1650,6 +1653,7 @@ impl Config {
             }
             set(&mut config.lld_mode, lld_mode);
             set(&mut config.lld_enabled, lld);
+            set(&mut config.llvm_bitcode_linker_enabled, llvm_bitcode_linker);
 
             if matches!(config.lld_mode, LldMode::SelfContained)
                 && !config.lld_enabled

src/bootstrap/src/lib.rs

@@ -64,6 +64,7 @@ const LLVM_TOOLS: &[&str] = &[
     "llvm-ar",       // used for creating and modifying archive files
     "llvm-as",       // used to convert LLVM assembly to LLVM bitcode
     "llvm-dis",      // used to disassemble LLVM bitcode
+    "llvm-link",     // Used to link LLVM bitcode
     "llc",           // used to compile LLVM bytecode
     "opt",           // used to optimize LLVM bytecode
 ];

src/bootstrap/src/utils/change_tracker.rs

@@ -146,4 +146,9 @@ pub const CONFIG_CHANGE_HISTORY: &[ChangeInfo] = &[
         severity: ChangeSeverity::Info,
         summary: "a new `target.*.runner` option is available to specify a wrapper executable required to run tests for a target",
     },
+    ChangeInfo {
+        change_id: 117458,
+        severity: ChangeSeverity::Info,
+        summary: "New option `rust.llvm-bitcode-linker` that will build the llvm-bitcode-linker.",
+    },
 ];

src/ci/docker/host-x86_64/dist-various-2/Dockerfile

@@ -135,7 +135,7 @@ ENV TARGETS=$TARGETS,x86_64-unknown-uefi
 # Luckily one of the folders is /usr/local/include so symlink /usr/include/x86_64-linux-gnu/asm there
 RUN ln -s /usr/include/x86_64-linux-gnu/asm /usr/local/include/asm
 
-ENV RUST_CONFIGURE_ARGS --enable-extended --enable-lld --disable-docs \
+ENV RUST_CONFIGURE_ARGS --enable-extended --enable-lld --enable-llvm-bitcode-linker --disable-docs \
   --set target.wasm32-wasi.wasi-root=/wasm32-wasip1 \
   --set target.wasm32-wasip1.wasi-root=/wasm32-wasip1 \
   --set target.wasm32-wasi-preview1-threads.wasi-root=/wasm32-wasi-preview1-threads \

src/tools/llvm-bitcode-linker/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "llvm-bitcode-linker"
+version = "0.0.1"
+description = "A self-contained linker for llvm bitcode"
+license = "MIT OR Apache-2.0"
+edition = "2021"
+publish = false
+
+[dependencies]
+anyhow = "1.0"
+tracing = "0.1"
+tracing-subscriber = {version = "0.3.0", features = ["std"] }
+clap = { version = "4.3", features = ["derive"] }
+thiserror = "1.0.24"

src/tools/llvm-bitcode-linker/README.md

@@ -0,0 +1,5 @@
+# LLVM Bitcode Linker
+The LLVM bitcode linker can be used to link targets without any dependency on system libraries.
+The code will be linked in llvm-bc before compiling to native code. For some of these targets
+(e.g. ptx) there does not exist a sensible way to link the native format at all. A bitcode linker
+is required to link code compiled for such targets.

src/tools/llvm-bitcode-linker/src/bin/llvm-bitcode-linker.rs

@@ -0,0 +1,62 @@
+use std::path::PathBuf;
+
+use clap::Parser;
+
+use llvm_bitcode_linker::{Optimization, Session, Target};
+
+#[derive(Debug, Parser)]
+/// Linker for embedded code without any system dependencies
+pub struct Args {
+    /// Input files - objects, archives and static libraries.
+    ///
+    /// An archive can be, but not required to be, a Rust rlib.
+    files: Vec<PathBuf>,
+
+    /// A symbol that should be exported
+    #[arg(long)]
+    export_symbol: Vec<String>,
+
+    /// Input files directory
+    #[arg(short = 'L')]
+    input_dir: Vec<PathBuf>,
+
+    /// Target triple for which the code is compiled
+    #[arg(long)]
+    target: Target,
+
+    /// The target cpu
+    #[arg(long)]
+    target_cpu: Option<String>,
+
+    /// Write output to the filename
+    #[arg(short, long)]
+    output: PathBuf,
+
+    // Enable link time optimization
+    #[arg(long)]
+    lto: bool,
+
+    /// Emit debug information
+    #[arg(long)]
+    debug: bool,
+
+    /// The optimization level
+    #[arg(short = 'O', value_enum, default_value = "0")]
+    optimization: Optimization,
+}
+
+fn main() -> anyhow::Result<()> {
+    tracing_subscriber::FmtSubscriber::builder().with_max_level(tracing::Level::DEBUG).init();
+
+    let args = Args::parse();
+
+    let mut linker = Session::new(args.target, args.target_cpu, args.output);
+
+    linker.add_exported_symbols(args.export_symbol);
+
+    for rlib in args.files {
+        linker.add_file(rlib);
+    }
+
+    linker.lto(args.optimization, args.debug)
+}

src/tools/llvm-bitcode-linker/src/lib.rs

@@ -0,0 +1,7 @@
+mod linker;
+mod opt;
+mod target;
+
+pub use linker::Session;
+pub use opt::Optimization;
+pub use target::Target;

src/tools/llvm-bitcode-linker/src/linker.rs

@@ -0,0 +1,163 @@
+use std::path::PathBuf;
+
+use anyhow::Context;
+
+use crate::Optimization;
+use crate::Target;
+
+#[derive(Debug)]
+pub struct Session {
+    target: Target,
+    cpu: Option<String>,
+    symbols: Vec<String>,
+
+    /// A file that `llvm-link` supports, like a bitcode file or an archive.
+    files: Vec<PathBuf>,
+
+    // Output files
+    link_path: PathBuf,
+    opt_path: PathBuf,
+    sym_path: PathBuf,
+    out_path: PathBuf,
+}
+
+impl Session {
+    pub fn new(target: crate::Target, cpu: Option<String>, out_path: PathBuf) -> Self {
+        let link_path = out_path.with_extension("o");
+        let opt_path = out_path.with_extension("optimized.o");
+        let sym_path = out_path.with_extension("symbols.txt");
+
+        Session {
+            target,
+            cpu,
+            symbols: Vec::new(),
+            files: Vec::new(),
+            link_path,
+            opt_path,
+            sym_path,
+            out_path,
+        }
+    }
+
+    /// Add a file, like an rlib or bitcode file that should be linked
+    pub fn add_file(&mut self, path: PathBuf) {
+        self.files.push(path);
+    }
+
+    /// Add a Vec of symbols to the list of exported symbols
+    pub fn add_exported_symbols(&mut self, symbols: Vec<String>) {
+        self.symbols.extend(symbols);
+    }
+
+    /// Reads every file that was added to the session and link them without optimization.
+    ///
+    /// The resulting artifact will be written to a file that can later be read to perform
+    /// optimizations and/or compilation from bitcode to the final artifact.
+    fn link(&mut self) -> anyhow::Result<()> {
+        tracing::info!("Linking {} files using llvm-link", self.files.len());
+
+        let llvm_link_output = std::process::Command::new("llvm-link")
+            .arg("--ignore-non-bitcode")
+            .args(&self.files)
+            .arg("-o")
+            .arg(&self.link_path)
+            .output()
+            .unwrap();
+
+        if !llvm_link_output.status.success() {
+            tracing::error!(
+                "llvm-link returned with Exit status: {}\n stdout: {}\n stderr: {}",
+                llvm_link_output.status,
+                String::from_utf8(llvm_link_output.stdout).unwrap(),
+                String::from_utf8(llvm_link_output.stderr).unwrap(),
+            );
+            anyhow::bail!("llvm-link failed to link files {:?}", self.files);
+        }
+
+        Ok(())
+    }
+
+    /// Optimize and compile to native format using `opt` and `llc`
+    ///
+    /// Before this can be called `link` needs to be called
+    fn optimize(&mut self, optimization: Optimization, mut debug: bool) -> anyhow::Result<()> {
+        let mut passes = format!("default<{}>", optimization);
+
+        // FIXME(@kjetilkjeka) Debug symbol generation is broken for nvptx64 so we must remove them even in debug mode
+        if debug && self.target == crate::Target::Nvptx64NvidiaCuda {
+            tracing::warn!("nvptx64 target detected - stripping debug symbols");
+            debug = false;
+        }
+
+        // We add an internalize pass as the rust compiler as we require exported symbols to be explicitly marked
+        passes.push_str(",internalize,globaldce");
+        let symbol_file_content = self.symbols.iter().fold(String::new(), |s, x| s + &x + "\n");
+        std::fs::write(&self.sym_path, symbol_file_content)
+            .context(format!("Failed to write symbol file: {}", self.sym_path.display()))?;
+
+        tracing::info!("optimizing bitcode with passes: {}", passes);
+        let mut opt_cmd = std::process::Command::new("opt");
+        opt_cmd
+            .arg(&self.link_path)
+            .arg("-o")
+            .arg(&self.opt_path)
+            .arg(format!("--internalize-public-api-file={}", self.sym_path.display()))
+            .arg(format!("--passes={}", passes));
+
+        if !debug {
+            opt_cmd.arg("--strip-debug");
+        }
+
+        let opt_output = opt_cmd.output().unwrap();
+
+        if !opt_output.status.success() {
+            tracing::error!(
+                "opt returned with Exit status: {}\n stdout: {}\n stderr: {}",
+                opt_output.status,
+                String::from_utf8(opt_output.stdout).unwrap(),
+                String::from_utf8(opt_output.stderr).unwrap(),
+            );
+            anyhow::bail!("opt failed optimize bitcode: {}", self.link_path.display());
+        };
+
+        Ok(())
+    }
+
+    /// Compile the optimized bitcode file to native format using `llc`
+    ///
+    /// Before this can be called `optimize` needs to be called
+    fn compile(&mut self) -> anyhow::Result<()> {
+        let mut lcc_command = std::process::Command::new("llc");
+
+        if let Some(mcpu) = &self.cpu {
+            lcc_command.arg("--mcpu").arg(mcpu);
+        }
+
+        let lcc_output =
+            lcc_command.arg(&self.opt_path).arg("-o").arg(&self.out_path).output().unwrap();
+
+        if !lcc_output.status.success() {
+            tracing::error!(
+                "llc returned with Exit status: {}\n stdout: {}\n stderr: {}",
+                lcc_output.status,
+                String::from_utf8(lcc_output.stdout).unwrap(),
+                String::from_utf8(lcc_output.stderr).unwrap(),
+            );
+
+            anyhow::bail!(
+                "llc failed to compile {} into {}",
+                self.opt_path.display(),
+                self.out_path.display()
+            );
+        }
+
+        Ok(())
+    }
+
+    /// Links, optimizes and compiles to the native format
+    pub fn lto(&mut self, optimization: crate::Optimization, debug: bool) -> anyhow::Result<()> {
+        self.link()?;
+        self.optimize(optimization, debug)?;
+        self.compile()
+    }
+}

src/tools/llvm-bitcode-linker/src/opt.rs

@@ -0,0 +1,53 @@
+use std::fmt::Display;
+use std::fmt::Formatter;
+
+#[derive(Debug, Clone, Copy, Default, Hash, Eq, PartialEq, clap::ValueEnum)]
+pub enum Optimization {
+    #[default]
+    #[value(name = "0")]
+    O0,
+    #[value(name = "1")]
+    O1,
+    #[value(name = "2")]
+    O2,
+    #[value(name = "3")]
+    O3,
+    #[value(name = "s")]
+    Os,
+    #[value(name = "z")]
+    Oz,
+}
+
+#[derive(Debug, Clone, Copy, thiserror::Error)]
+/// An invalid optimization level
+#[error("invalid optimization level")]
+pub struct InvalidOptimizationLevel;
+
+impl std::str::FromStr for Optimization {
+    type Err = InvalidOptimizationLevel;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "0" | "O0" => Ok(Optimization::O0),
+            "1" | "O1" => Ok(Optimization::O1),
+            "2" | "O2" => Ok(Optimization::O2),
+            "3" | "O3" => Ok(Optimization::O3),
+            "s" | "Os" => Ok(Optimization::Os),
+            "z" | "Oz" => Ok(Optimization::Oz),
+            _ => Err(InvalidOptimizationLevel),
+        }
+    }
+}
+
+impl Display for Optimization {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        match *self {
+            Optimization::O0 => write!(f, "O0"),
+            Optimization::O1 => write!(f, "O1"),
+            Optimization::O2 => write!(f, "O2"),
+            Optimization::O3 => write!(f, "O3"),
+            Optimization::Os => write!(f, "Os"),
+            Optimization::Oz => write!(f, "Oz"),
+        }
+    }
+}

src/tools/llvm-bitcode-linker/src/target.rs

@@ -0,0 +1,20 @@
+#[derive(Clone, Copy, Debug, Eq, PartialEq, Hash, clap::ValueEnum)]
+pub enum Target {
+    Nvptx64NvidiaCuda,
+}
+
+#[derive(Debug, Clone, Copy, thiserror::Error)]
+/// The target is not supported by this linker
+#[error("unsupported target")]
+pub struct UnsupportedTarget;
+
+impl std::str::FromStr for Target {
+    type Err = UnsupportedTarget;
+
+    fn from_str(s: &str) -> Result<Target, UnsupportedTarget> {
+        match s {
+            "nvptx64-nvidia-cuda" => Ok(Target::Nvptx64NvidiaCuda),
+            _ => Err(UnsupportedTarget),
+        }
+    }
+}

src/tools/miri/tests/pass/alloc-access-tracking.rs

@@ -0,0 +1,25 @@
+#![feature(start)]
+#![no_std]
+//@compile-flags: -Zmiri-track-alloc-id=17 -Zmiri-track-alloc-accesses -Cpanic=abort
+//@only-target-linux: alloc IDs differ between OSes for some reason
+
+extern "Rust" {
+    fn miri_alloc(size: usize, align: usize) -> *mut u8;
+    fn miri_dealloc(ptr: *mut u8, size: usize, align: usize);
+}
+
+#[start]
+fn start(_: isize, _: *const *const u8) -> isize {
+    unsafe {
+        let ptr = miri_alloc(123, 1);
+        *ptr = 42; // Crucially, only a write is printed here, no read!
+        assert_eq!(*ptr, 42);
+        miri_dealloc(ptr, 123, 1);
+    }
+    0
+}
+
+#[panic_handler]
+fn panic_handler(_: &core::panic::PanicInfo) -> ! {
+    loop {}
+}

src/tools/miri/tests/pass/alloc-access-tracking.stderr

@@ -0,0 +1,37 @@
+note: tracking was triggered
+  --> $DIR/alloc-access-tracking.rs:LL:CC
+   |
+LL |         let ptr = miri_alloc(123, 1);
+   |                   ^^^^^^^^^^^^^^^^^^ created Miri bare-metal heap allocation of 123 bytes (alignment ALIGN bytes) with id 17
+   |
+   = note: BACKTRACE:
+   = note: inside `start` at $DIR/alloc-access-tracking.rs:LL:CC
+
+note: tracking was triggered
+  --> $DIR/alloc-access-tracking.rs:LL:CC
+   |
+LL |         *ptr = 42; // Crucially, only a write is printed here, no read!
+   |         ^^^^^^^^^ write access to allocation with id 17
+   |
+   = note: BACKTRACE:
+   = note: inside `start` at $DIR/alloc-access-tracking.rs:LL:CC
+
+note: tracking was triggered
+  --> $DIR/alloc-access-tracking.rs:LL:CC
+   |
+LL |         assert_eq!(*ptr, 42);
+   |         ^^^^^^^^^^^^^^^^^^^^ read access to allocation with id 17
+   |
+   = note: BACKTRACE:
+   = note: inside `start` at RUSTLIB/core/src/macros/mod.rs:LL:CC
+   = note: this note originates in the macro `assert_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+note: tracking was triggered
+  --> $DIR/alloc-access-tracking.rs:LL:CC
+   |
+LL |         miri_dealloc(ptr, 123, 1);
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^ freed allocation with id 17
+   |
+   = note: BACKTRACE:
+   = note: inside `start` at $DIR/alloc-access-tracking.rs:LL:CC
+

tests/assembly/nvptx-arch-default.rs

@@ -1,7 +1,6 @@
 //@ assembly-output: ptx-linker
-//@ compile-flags: --crate-type cdylib
+//@ compile-flags: --crate-type cdylib -Z unstable-options -Clinker-flavor=llbc
 //@ only-nvptx64
-//@ ignore-nvptx64
 
 #![no_std]
 

tests/assembly/nvptx-arch-emit-asm.rs

@@ -1,7 +1,6 @@
 //@ assembly-output: emit-asm
 //@ compile-flags: --crate-type rlib
 //@ only-nvptx64
-//@ ignore-nvptx64
 
 #![no_std]
 

tests/assembly/nvptx-arch-target-cpu.rs

@@ -1,7 +1,6 @@
 //@ assembly-output: ptx-linker
-//@ compile-flags: --crate-type cdylib -C target-cpu=sm_50
+//@ compile-flags: --crate-type cdylib -C target-cpu=sm_50 -Z unstable-options -Clinker-flavor=llbc
 //@ only-nvptx64
-//@ ignore-nvptx64
 
 #![no_std]
 

tests/assembly/nvptx-kernel-abi/nvptx-kernel-args-abi-v7.rs

@@ -1,7 +1,6 @@
 //@ assembly-output: ptx-linker
-//@ compile-flags: --crate-type cdylib -C target-cpu=sm_86
+//@ compile-flags: --crate-type cdylib -C target-cpu=sm_86 -Z unstable-options -Clinker-flavor=llbc
 //@ only-nvptx64
-//@ ignore-nvptx64
 
 // The following ABI tests are made with nvcc 11.6 does.
 //
@@ -226,10 +225,11 @@ pub unsafe extern "ptx-kernel" fn f_byte_array_arg(_a: [u8; 5]) {}
 #[no_mangle]
 pub unsafe extern "ptx-kernel" fn f_float_array_arg(_a: [f32; 5]) {}
 
-// CHECK: .visible .entry f_u128_array_arg(
-// CHECK: .param .align 16 .b8 f_u128_array_arg_param_0[80]
-#[no_mangle]
-pub unsafe extern "ptx-kernel" fn f_u128_array_arg(_a: [u128; 5]) {}
+// FIXME: u128 started to break compilation with disabled CI
+// NO_CHECK: .visible .entry f_u128_array_arg(
+// NO_CHECK: .param .align 16 .b8 f_u128_array_arg_param_0[80]
+//#[no_mangle]
+//pub unsafe extern "ptx-kernel" fn f_u128_array_arg(_a: [u128; 5]) {}
 
 // CHECK: .visible .entry f_u32_slice_arg(
 // CHECK: .param .u64 f_u32_slice_arg_param_0
@@ -247,7 +247,6 @@ pub unsafe extern "ptx-kernel" fn f_tuple_u8_u8_arg(_a: (u8, u8)) {}
 #[no_mangle]
 pub unsafe extern "ptx-kernel" fn f_tuple_u32_u32_arg(_a: (u32, u32)) {}
 
-
 // CHECK: .visible .entry f_tuple_u8_u8_u32_arg(
 // CHECK: .param .align 4 .b8 f_tuple_u8_u8_u32_arg_param_0[8]
 #[no_mangle]

tests/assembly/nvptx-safe-naming.rs

@@ -1,7 +1,6 @@
 //@ assembly-output: ptx-linker
-//@ compile-flags: --crate-type cdylib
+//@ compile-flags: --crate-type cdylib -Z unstable-options -Clinker-flavor=llbc
 //@ only-nvptx64
-//@ ignore-nvptx64
 
 #![feature(abi_ptx)]
 #![no_std]
@@ -10,7 +9,7 @@
 extern crate breakpoint_panic_handler;
 
 // Verify function name doesn't contain unacceaptable characters.
-// CHECK: .func (.param .b32 func_retval0) [[IMPL_FN:[a-zA-Z0-9$_]+square[a-zA-Z0-9$_]+]](
+// CHECK: .func (.param .b32 func_retval0) [[IMPL_FN:[a-zA-Z0-9$_]+square[a-zA-Z0-9$_]+]]
 
 // CHECK-LABEL: .visible .entry top_kernel(
 #[no_mangle]

tests/codegen/dst-offset.rs

@@ -25,9 +25,9 @@ struct Dst<T: ?Sized> {
 pub fn dst_dyn_trait_offset(s: &Dst<dyn Drop>) -> &dyn Drop {
 // The alignment of dyn trait is unknown, so we compute the offset based on align from the vtable.
 
-// CHECK: [[SIZE_PTR:%[0-9]+]] = getelementptr inbounds {{.+}} [[VTABLE_PTR]]
+// CHECK: [[SIZE_PTR:%[0-9]+]] = getelementptr inbounds i8, ptr [[VTABLE_PTR]]
 // CHECK: load [[USIZE]], ptr [[SIZE_PTR]]
-// CHECK: [[ALIGN_PTR:%[0-9]+]] = getelementptr inbounds {{.+}} [[VTABLE_PTR]]
+// CHECK: [[ALIGN_PTR:%[0-9]+]] = getelementptr inbounds i8, ptr [[VTABLE_PTR]]
 // CHECK: load [[USIZE]], ptr [[ALIGN_PTR]]
 
 // CHECK: getelementptr inbounds i8, ptr [[DATA_PTR]]

tests/codegen/vtable-upcast.rs

@@ -0,0 +1,85 @@
+//! This file tests that we correctly generate GEP instructions for vtable upcasting.
+//@ compile-flags: -C no-prepopulate-passes -Copt-level=0
+
+#![crate_type = "lib"]
+#![feature(trait_upcasting)]
+
+pub trait Base {
+    fn base(&self);
+}
+
+pub trait A : Base {
+    fn a(&self);
+}
+
+pub trait B : Base {
+    fn b(&self);
+}
+
+pub trait Diamond : A + B {
+    fn diamond(&self);
+}
+
+// CHECK-LABEL: upcast_a_to_base
+#[no_mangle]
+pub fn upcast_a_to_base(x: &dyn A) -> &dyn Base {
+    // Requires no adjustment, since its vtable is extended from `Base`.
+
+    // CHECK: start:
+    // CHECK-NEXT: insertvalue
+    // CHECK-NEXT: insertvalue
+    // CHECK-NEXT: ret
+    x as &dyn Base
+}
+
+// CHECK-LABEL: upcast_b_to_base
+#[no_mangle]
+pub fn upcast_b_to_base(x: &dyn B) -> &dyn Base {
+    // Requires no adjustment, since its vtable is extended from `Base`.
+
+    // CHECK: start:
+    // CHECK-NEXT: insertvalue
+    // CHECK-NEXT: insertvalue
+    // CHECK-NEXT: ret
+    x as &dyn Base
+}
+
+// CHECK-LABEL: upcast_diamond_to_a
+#[no_mangle]
+pub fn upcast_diamond_to_a(x: &dyn Diamond) -> &dyn A {
+    // Requires no adjustment, since its vtable is extended from `A` (as the first supertrait).
+
+    // CHECK: start:
+    // CHECK-NEXT: insertvalue
+    // CHECK-NEXT: insertvalue
+    // CHECK-NEXT: ret
+    x as &dyn A
+}
+
+// CHECK-LABEL: upcast_diamond_to_b
+// CHECK-SAME: (ptr align {{[0-9]+}} [[DATA_PTR:%.+]], ptr align {{[0-9]+}} [[VTABLE_PTR:%.+]])
+#[no_mangle]
+pub fn upcast_diamond_to_b(x: &dyn Diamond) -> &dyn B {
+    // Requires adjustment, since it's a non-first supertrait.
+
+    // CHECK: start:
+    // CHECK-NEXT: [[UPCAST_SLOT_PTR:%.+]] = getelementptr inbounds i8, ptr [[VTABLE_PTR]]
+    // CHECK-NEXT: [[UPCAST_VTABLE_PTR:%.+]] = load ptr, ptr [[UPCAST_SLOT_PTR]]
+    // CHECK-NEXT: [[FAT_PTR_1:%.+]] = insertvalue { ptr, ptr } poison, ptr [[DATA_PTR]], 0
+    // CHECK-NEXT: [[FAT_PTR_2:%.+]] = insertvalue { ptr, ptr } [[FAT_PTR_1]], ptr [[UPCAST_VTABLE_PTR]], 1
+    // CHECK-NEXT: ret { ptr, ptr } [[FAT_PTR_2]]
+    x as &dyn B
+}
+
+// CHECK-LABEL: upcast_diamond_to_b
+#[no_mangle]
+pub fn upcast_diamond_to_base(x: &dyn Diamond) -> &dyn Base {
+    // Requires no adjustment, since `Base` is the first supertrait of `A`,
+    // which is the first supertrait of `Diamond`.
+
+    // CHECK: start:
+    // CHECK-NEXT: insertvalue
+    // CHECK-NEXT: insertvalue
+    // CHECK-NEXT: ret
+    x as &dyn Base
+}

tests/ui/associated-consts/assoc-const-eq-supertraits.rs

@@ -0,0 +1,16 @@
+// Regression test for issue #118040.
+// Ensure that we support assoc const eq bounds where the assoc const comes from a supertrait.
+
+//@ check-pass
+
+#![feature(associated_const_equality)]
+
+trait Trait: SuperTrait {}
+trait SuperTrait: SuperSuperTrait<i32> {}
+trait SuperSuperTrait<T> {
+    const K: T;
+}
+
+fn take(_: impl Trait<K = 0>) {}
+
+fn main() {}

tests/ui/associated-consts/assoc-const-eq-ty-alias-noninteracting.rs

@@ -1,21 +1,25 @@
 // Regression test for issue #112560.
 // Respect the fact that (associated) types and constants live in different namespaces and
 // therefore equality bounds involving identically named associated items don't conflict if
-// their kind (type vs. const) differs.
-
-// FIXME(fmease): Extend this test to cover supertraits again
-// once #118040 is fixed. See initial version of PR #118360.
+// their kind (type vs. const) differs. This obviously extends to supertraits.
 
 //@ check-pass
 
 #![feature(associated_const_equality)]
 
-trait Trait {
+trait Trait: SuperTrait {
     type N;
+    type Q;
 
     const N: usize;
 }
 
-fn take(_: impl Trait<N = 0, N = ()>) {}
+trait SuperTrait {
+    const Q: &'static str;
+}
+
+fn take0(_: impl Trait<N = 0, N = ()>) {}
+
+fn take1(_: impl Trait<Q = "...", Q = [()]>) {}
 
 fn main() {}

tests/ui/associated-inherent-types/bugs/wf-check-skipped.next.stderr

@@ -0,0 +1,8 @@
+error: the type `Foo::Bar<Vec<[u32]>>` is not well-formed
+  --> $DIR/wf-check-skipped.rs:17:14
+   |
+LL | fn main() -> Foo::Bar::<Vec<[u32]>> {}
+   |              ^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+

tests/ui/associated-inherent-types/bugs/wf-check-skipped.rs

@@ -1,11 +1,13 @@
-//@ known-bug: #100041
-//@ check-pass
+//@ revisions: current next
+//@[next] compile-flags: -Znext-solver
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[current] known-bug: #100041
+//@[current] check-pass
+// FIXME(inherent_associated_types): This should fail.
 
 #![feature(inherent_associated_types)]
 #![allow(incomplete_features)]
 
-// FIXME(inherent_associated_types): This should fail.
-
 struct Foo;
 
 impl Foo {
@@ -13,3 +15,4 @@ impl Foo {
 }
 
 fn main() -> Foo::Bar::<Vec<[u32]>> {}
+//[next]~^ ERROR the type `Foo::Bar<Vec<[u32]>>` is not well-formed

tests/ui/associated-inherent-types/inference.rs

@@ -1,6 +1,7 @@
 // Testing inference capabilities.
 //@ check-pass
 //@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
 //@[next] compile-flags: -Znext-solver
 
 #![feature(inherent_associated_types)]

tests/ui/associated-types/defaults-unsound-62211-1.current.stderr

@@ -1,12 +1,12 @@
 error[E0277]: `Self` doesn't implement `std::fmt::Display`
-  --> $DIR/defaults-unsound-62211-1.rs:20:96
+  --> $DIR/defaults-unsound-62211-1.rs:26:96
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                                                                                                ^^^^ `Self` cannot be formatted with the default formatter
    |
    = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
 note: required by a bound in `UncheckedCopy::Output`
-  --> $DIR/defaults-unsound-62211-1.rs:20:86
+  --> $DIR/defaults-unsound-62211-1.rs:26:86
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                                                                                      ^^^^^^^ required by this bound in `UncheckedCopy::Output`
@@ -16,13 +16,13 @@ LL | trait UncheckedCopy: Sized + std::fmt::Display {
    |                            +++++++++++++++++++
 
 error[E0277]: cannot add-assign `&'static str` to `Self`
-  --> $DIR/defaults-unsound-62211-1.rs:20:96
+  --> $DIR/defaults-unsound-62211-1.rs:26:96
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                                                                                                ^^^^ no implementation for `Self += &'static str`
    |
 note: required by a bound in `UncheckedCopy::Output`
-  --> $DIR/defaults-unsound-62211-1.rs:20:47
+  --> $DIR/defaults-unsound-62211-1.rs:26:47
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                                               ^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `UncheckedCopy::Output`
@@ -32,13 +32,13 @@ LL | trait UncheckedCopy: Sized + AddAssign<&'static str> {
    |                            +++++++++++++++++++++++++
 
 error[E0277]: the trait bound `Self: Deref` is not satisfied
-  --> $DIR/defaults-unsound-62211-1.rs:20:96
+  --> $DIR/defaults-unsound-62211-1.rs:26:96
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                                                                                                ^^^^ the trait `Deref` is not implemented for `Self`
    |
 note: required by a bound in `UncheckedCopy::Output`
-  --> $DIR/defaults-unsound-62211-1.rs:20:25
+  --> $DIR/defaults-unsound-62211-1.rs:26:25
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                         ^^^^^^^^^^^^^^^^^^^ required by this bound in `UncheckedCopy::Output`
@@ -48,13 +48,13 @@ LL | trait UncheckedCopy: Sized + Deref {
    |                            +++++++
 
 error[E0277]: the trait bound `Self: Copy` is not satisfied
-  --> $DIR/defaults-unsound-62211-1.rs:20:96
+  --> $DIR/defaults-unsound-62211-1.rs:26:96
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                                                                                                ^^^^ the trait `Copy` is not implemented for `Self`
    |
 note: required by a bound in `UncheckedCopy::Output`
-  --> $DIR/defaults-unsound-62211-1.rs:20:18
+  --> $DIR/defaults-unsound-62211-1.rs:26:18
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                  ^^^^ required by this bound in `UncheckedCopy::Output`

tests/ui/associated-types/defaults-unsound-62211-1.next.stderr

@@ -0,0 +1,13 @@
+warning: calls to `std::mem::drop` with a value that implements `Copy` does nothing
+  --> $DIR/defaults-unsound-62211-1.rs:52:5
+   |
+LL |     drop(origin);
+   |     ^^^^^------^
+   |          |
+   |          argument has type `<T as UncheckedCopy>::Output`
+   |
+   = note: use `let _ = ...` to ignore the expression or result
+   = note: `#[warn(dropping_copy_types)]` on by default
+
+warning: 1 warning emitted
+

tests/ui/associated-types/defaults-unsound-62211-1.rs

@@ -1,3 +1,9 @@
+//@ revisions: current next
+//@[next] compile-flags: -Znext-solver
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] known-bug: rust-lang/trait-system-refactor-initiative#46
+//@[next] check-pass
+
 //! Regression test for https://github.com/rust-lang/rust/issues/62211
 //!
 //! The old implementation of defaults did not check whether the provided
@@ -18,10 +24,10 @@ trait UncheckedCopy: Sized {
     // This Output is said to be Copy. Yet we default to Self
     // and it's accepted, not knowing if Self ineed is Copy
     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
-    //~^ ERROR the trait bound `Self: Copy` is not satisfied
-    //~| ERROR the trait bound `Self: Deref` is not satisfied
-    //~| ERROR cannot add-assign `&'static str` to `Self`
-    //~| ERROR `Self` doesn't implement `std::fmt::Display`
+    //[current]~^ ERROR the trait bound `Self: Copy` is not satisfied
+    //[current]~| ERROR the trait bound `Self: Deref` is not satisfied
+    //[current]~| ERROR cannot add-assign `&'static str` to `Self`
+    //[current]~| ERROR `Self` doesn't implement `std::fmt::Display`
 
     // We said the Output type was Copy, so we can Copy it freely!
     fn unchecked_copy(other: &Self::Output) -> Self::Output {

tests/ui/associated-types/defaults-unsound-62211-2.current.stderr

@@ -1,12 +1,12 @@
 error[E0277]: `Self` doesn't implement `std::fmt::Display`
-  --> $DIR/defaults-unsound-62211-2.rs:20:96
+  --> $DIR/defaults-unsound-62211-2.rs:26:96
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                                                                                                ^^^^ `Self` cannot be formatted with the default formatter
    |
    = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
 note: required by a bound in `UncheckedCopy::Output`
-  --> $DIR/defaults-unsound-62211-2.rs:20:86
+  --> $DIR/defaults-unsound-62211-2.rs:26:86
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                                                                                      ^^^^^^^ required by this bound in `UncheckedCopy::Output`
@@ -16,13 +16,13 @@ LL | trait UncheckedCopy: Sized + std::fmt::Display {
    |                            +++++++++++++++++++
 
 error[E0277]: cannot add-assign `&'static str` to `Self`
-  --> $DIR/defaults-unsound-62211-2.rs:20:96
+  --> $DIR/defaults-unsound-62211-2.rs:26:96
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                                                                                                ^^^^ no implementation for `Self += &'static str`
    |
 note: required by a bound in `UncheckedCopy::Output`
-  --> $DIR/defaults-unsound-62211-2.rs:20:47
+  --> $DIR/defaults-unsound-62211-2.rs:26:47
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                                               ^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `UncheckedCopy::Output`
@@ -32,13 +32,13 @@ LL | trait UncheckedCopy: Sized + AddAssign<&'static str> {
    |                            +++++++++++++++++++++++++
 
 error[E0277]: the trait bound `Self: Deref` is not satisfied
-  --> $DIR/defaults-unsound-62211-2.rs:20:96
+  --> $DIR/defaults-unsound-62211-2.rs:26:96
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                                                                                                ^^^^ the trait `Deref` is not implemented for `Self`
    |
 note: required by a bound in `UncheckedCopy::Output`
-  --> $DIR/defaults-unsound-62211-2.rs:20:25
+  --> $DIR/defaults-unsound-62211-2.rs:26:25
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                         ^^^^^^^^^^^^^^^^^^^ required by this bound in `UncheckedCopy::Output`
@@ -48,13 +48,13 @@ LL | trait UncheckedCopy: Sized + Deref {
    |                            +++++++
 
 error[E0277]: the trait bound `Self: Copy` is not satisfied
-  --> $DIR/defaults-unsound-62211-2.rs:20:96
+  --> $DIR/defaults-unsound-62211-2.rs:26:96
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                                                                                                ^^^^ the trait `Copy` is not implemented for `Self`
    |
 note: required by a bound in `UncheckedCopy::Output`
-  --> $DIR/defaults-unsound-62211-2.rs:20:18
+  --> $DIR/defaults-unsound-62211-2.rs:26:18
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                  ^^^^ required by this bound in `UncheckedCopy::Output`

tests/ui/associated-types/defaults-unsound-62211-2.next.stderr

@@ -0,0 +1,13 @@
+warning: calls to `std::mem::drop` with a value that implements `Copy` does nothing
+  --> $DIR/defaults-unsound-62211-2.rs:52:5
+   |
+LL |     drop(origin);
+   |     ^^^^^------^
+   |          |
+   |          argument has type `<T as UncheckedCopy>::Output`
+   |
+   = note: use `let _ = ...` to ignore the expression or result
+   = note: `#[warn(dropping_copy_types)]` on by default
+
+warning: 1 warning emitted
+

tests/ui/associated-types/defaults-unsound-62211-2.rs

@@ -1,3 +1,9 @@
+//@ revisions: current next
+//@[next] compile-flags: -Znext-solver
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] known-bug: rust-lang/trait-system-refactor-initiative#46
+//@[next] check-pass
+
 //! Regression test for https://github.com/rust-lang/rust/issues/62211
 //!
 //! The old implementation of defaults did not check whether the provided
@@ -18,10 +24,10 @@ trait UncheckedCopy: Sized {
     // This Output is said to be Copy. Yet we default to Self
     // and it's accepted, not knowing if Self ineed is Copy
     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
-    //~^ ERROR the trait bound `Self: Copy` is not satisfied
-    //~| ERROR the trait bound `Self: Deref` is not satisfied
-    //~| ERROR cannot add-assign `&'static str` to `Self`
-    //~| ERROR `Self` doesn't implement `std::fmt::Display`
+    //[current]~^ ERROR the trait bound `Self: Copy` is not satisfied
+    //[current]~| ERROR the trait bound `Self: Deref` is not satisfied
+    //[current]~| ERROR cannot add-assign `&'static str` to `Self`
+    //[current]~| ERROR `Self` doesn't implement `std::fmt::Display`
 
     // We said the Output type was Copy, so we can Copy it freely!
     fn unchecked_copy(other: &Self::Output) -> Self::Output {

tests/ui/async-await/async-closures/is-fn.rs

@@ -2,6 +2,7 @@
 //@ edition:2021
 //@ build-pass
 //@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
 //@[next] compile-flags: -Znext-solver
 
 #![feature(async_closure)]

tests/ui/async-await/async-closures/once.rs

@@ -2,6 +2,7 @@
 //@ edition:2021
 //@ build-pass
 //@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
 //@[next] compile-flags: -Znext-solver
 
 #![feature(async_closure)]

tests/ui/async-await/async-fn/higher-ranked-async-fn.rs

@@ -1,6 +1,7 @@
 //@ aux-build:block-on.rs
 //@ edition:2018
 //@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
 //@[next] compile-flags: -Znext-solver
 //@ build-pass (since it ICEs during mono)
 

tests/ui/async-await/async-fn/project.rs

@@ -1,5 +1,6 @@
 //@ edition:2018
 //@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
 //@[next] compile-flags: -Znext-solver
 //@ check-pass
 

tests/ui/async-await/normalize-output-in-signature-deduction.rs

@@ -1,5 +1,6 @@
 //@ edition:2021
 //@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
 //@[next] compile-flags: -Znext-solver
 //@ check-pass
 

tests/ui/async-await/return-type-notation/normalizing-self-auto-trait-issue-109924.current.stderr

@@ -1,5 +1,5 @@
 warning: the feature `return_type_notation` is incomplete and may not be safe to use and/or cause compiler crashes
-  --> $DIR/normalizing-self-auto-trait-issue-109924.rs:6:12
+  --> $DIR/normalizing-self-auto-trait-issue-109924.rs:7:12
    |
 LL | #![feature(return_type_notation)]
    |            ^^^^^^^^^^^^^^^^^^^^

tests/ui/async-await/return-type-notation/normalizing-self-auto-trait-issue-109924.next.stderr

@@ -1,5 +1,5 @@
 warning: the feature `return_type_notation` is incomplete and may not be safe to use and/or cause compiler crashes
-  --> $DIR/normalizing-self-auto-trait-issue-109924.rs:6:12
+  --> $DIR/normalizing-self-auto-trait-issue-109924.rs:7:12
    |
 LL | #![feature(return_type_notation)]
    |            ^^^^^^^^^^^^^^^^^^^^

tests/ui/async-await/return-type-notation/normalizing-self-auto-trait-issue-109924.rs

@@ -1,5 +1,6 @@
 //@ check-pass
 //@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
 //@[next] compile-flags: -Znext-solver
 //@ edition:2021
 

tests/ui/attributes/unix_sigpipe/unix_sigpipe-crate.rs

@@ -1,4 +1,4 @@
 #![feature(unix_sigpipe)]
-#![unix_sigpipe = "inherit"] //~ error: `unix_sigpipe` attribute cannot be used at crate level
+#![unix_sigpipe = "sig_dfl"] //~ error: `unix_sigpipe` attribute cannot be used at crate level
 
 fn main() {}

tests/ui/attributes/unix_sigpipe/unix_sigpipe-crate.stderr

@@ -1,7 +1,7 @@
 error: `unix_sigpipe` attribute cannot be used at crate level
   --> $DIR/unix_sigpipe-crate.rs:2:1
    |
-LL | #![unix_sigpipe = "inherit"]
+LL | #![unix_sigpipe = "sig_dfl"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 LL |
 LL | fn main() {}
@@ -9,8 +9,8 @@ LL | fn main() {}
    |
 help: perhaps you meant to use an outer attribute
    |
-LL - #![unix_sigpipe = "inherit"]
-LL + #[unix_sigpipe = "inherit"]
+LL - #![unix_sigpipe = "sig_dfl"]
+LL + #[unix_sigpipe = "sig_dfl"]
    |
 
 error: aborting due to 1 previous error

tests/ui/attributes/unix_sigpipe/unix_sigpipe-list.rs

@@ -1,4 +1,4 @@
 #![feature(unix_sigpipe)]
 
-#[unix_sigpipe(inherit)] //~ error: malformed `unix_sigpipe` attribute input
+#[unix_sigpipe(sig_dfl)] //~ error: malformed `unix_sigpipe` attribute input
 fn main() {}

tests/ui/attributes/unix_sigpipe/unix_sigpipe-list.stderr

@@ -1,7 +1,7 @@
 error: malformed `unix_sigpipe` attribute input
   --> $DIR/unix_sigpipe-list.rs:3:1
    |
-LL | #[unix_sigpipe(inherit)]
+LL | #[unix_sigpipe(sig_dfl)]
    | ^^^^^^^^^^^^^^^^^^^^^^^^ help: must be of the form: `#[unix_sigpipe = "inherit|sig_ign|sig_dfl"]`
 
 error: aborting due to 1 previous error

tests/ui/attributes/unix_sigpipe/unix_sigpipe-non-main-fn.rs

@@ -1,6 +1,6 @@
 #![feature(unix_sigpipe)]
 
-#[unix_sigpipe = "inherit"] //~ error: `unix_sigpipe` attribute can only be used on `fn main()`
+#[unix_sigpipe = "sig_dfl"] //~ error: `unix_sigpipe` attribute can only be used on `fn main()`
 fn f() {}
 
 fn main() {}

tests/ui/attributes/unix_sigpipe/unix_sigpipe-non-main-fn.stderr

@@ -1,7 +1,7 @@
 error: `unix_sigpipe` attribute can only be used on `fn main()`
   --> $DIR/unix_sigpipe-non-main-fn.rs:3:1
    |
-LL | #[unix_sigpipe = "inherit"]
+LL | #[unix_sigpipe = "sig_dfl"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 1 previous error

tests/ui/attributes/unix_sigpipe/unix_sigpipe-non-root-main.rs

@@ -1,7 +1,7 @@
 #![feature(unix_sigpipe)]
 
 mod m {
-    #[unix_sigpipe = "inherit"] //~ error: `unix_sigpipe` attribute can only be used on root `fn main()`
+    #[unix_sigpipe = "sig_dfl"] //~ error: `unix_sigpipe` attribute can only be used on root `fn main()`
     fn main() {}
 }
 

tests/ui/attributes/unix_sigpipe/unix_sigpipe-non-root-main.stderr

@@ -1,7 +1,7 @@
 error: `unix_sigpipe` attribute can only be used on root `fn main()`
   --> $DIR/unix_sigpipe-non-root-main.rs:4:5
    |
-LL |     #[unix_sigpipe = "inherit"]
+LL |     #[unix_sigpipe = "sig_dfl"]
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 1 previous error

tests/ui/attributes/unix_sigpipe/unix_sigpipe-start.rs

@@ -2,5 +2,5 @@
 #![feature(unix_sigpipe)]
 
 #[start]
-#[unix_sigpipe = "inherit"] //~ error: `unix_sigpipe` attribute can only be used on `fn main()`
+#[unix_sigpipe = "sig_dfl"] //~ error: `unix_sigpipe` attribute can only be used on `fn main()`
 fn custom_start(argc: isize, argv: *const *const u8) -> isize { 0 }

tests/ui/attributes/unix_sigpipe/unix_sigpipe-start.stderr

@@ -1,7 +1,7 @@
 error: `unix_sigpipe` attribute can only be used on `fn main()`
   --> $DIR/unix_sigpipe-start.rs:5:1
    |
-LL | #[unix_sigpipe = "inherit"]
+LL | #[unix_sigpipe = "sig_dfl"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 1 previous error