From 94e940dd3034f1821c3a72900e9a274f791a7e3a Mon Sep 17 00:00:00 2001
From: Gary Guo <gary@garyguo.net>
Date: Fri, 29 Oct 2021 15:51:52 +0100
Subject: [PATCH 1/2] Collect `panic/panic_bounds_check` during
 monomorphization

---
 compiler/rustc_monomorphize/src/collector.rs  | 13 ++++-
 .../item-collection/implicit-panic-call.rs    | 58 +++++++++++++++++++
 2 files changed, 69 insertions(+), 2 deletions(-)
 create mode 100644 src/test/codegen-units/item-collection/implicit-panic-call.rs

diff --git a/compiler/rustc_monomorphize/src/collector.rs b/compiler/rustc_monomorphize/src/collector.rs
index 5147408210e..59988e69b5d 100644
--- a/compiler/rustc_monomorphize/src/collector.rs
+++ b/compiler/rustc_monomorphize/src/collector.rs
@@ -806,13 +806,22 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> {
                     }
                 }
             }
+            mir::TerminatorKind::Assert { ref msg, .. } => {
+                let lang_item = match msg {
+                    mir::AssertKind::BoundsCheck { .. } => LangItem::PanicBoundsCheck,
+                    _ => LangItem::Panic,
+                };
+                let instance = Instance::mono(tcx, tcx.require_lang_item(lang_item, Some(source)));
+                if should_codegen_locally(tcx, &instance) {
+                    self.output.push(create_fn_mono_item(tcx, instance, source));
+                }
+            }
             mir::TerminatorKind::Goto { .. }
             | mir::TerminatorKind::SwitchInt { .. }
             | mir::TerminatorKind::Resume
             | mir::TerminatorKind::Abort
             | mir::TerminatorKind::Return
-            | mir::TerminatorKind::Unreachable
-            | mir::TerminatorKind::Assert { .. } => {}
+            | mir::TerminatorKind::Unreachable => {}
             mir::TerminatorKind::GeneratorDrop
             | mir::TerminatorKind::Yield { .. }
             | mir::TerminatorKind::FalseEdge { .. }
diff --git a/src/test/codegen-units/item-collection/implicit-panic-call.rs b/src/test/codegen-units/item-collection/implicit-panic-call.rs
new file mode 100644
index 00000000000..abec7ad50ae
--- /dev/null
+++ b/src/test/codegen-units/item-collection/implicit-panic-call.rs
@@ -0,0 +1,58 @@
+// compile-flags:-Zprint-mono-items=lazy
+
+// rust-lang/rust#90405
+// Ensure implicit panic calls are collected
+
+#![feature(lang_items)]
+#![feature(no_core)]
+#![crate_type = "lib"]
+#![no_core]
+#![no_std]
+
+#[lang = "panic_location"]
+struct Location<'a> {
+    _file: &'a str,
+    _line: u32,
+    _col: u32,
+}
+
+#[lang = "panic"]
+#[inline]
+#[track_caller]
+fn panic(_: &'static str) -> ! {
+    loop {}
+}
+
+#[lang = "sized"]
+trait Sized {}
+
+#[lang = "copy"]
+trait Copy {}
+
+#[lang = "freeze"]
+trait Freeze {}
+
+impl Copy for i32 {}
+
+#[lang = "div"]
+trait Div<Rhs = Self> {
+    type Output;
+    fn div(self, rhs: Rhs) -> Self::Output;
+}
+
+impl Div for i32 {
+    type Output = i32;
+    fn div(self, rhs: i32) -> i32 {
+        self / rhs
+    }
+}
+
+#[allow(unconditional_panic)]
+pub fn foo() {
+    // This implicitly generates a panic call.
+    let _ = 1 / 0;
+}
+
+//~ MONO_ITEM fn foo
+//~ MONO_ITEM fn <i32 as Div>::div
+//~ MONO_ITEM fn panic

From 4d619d92aea769d1646ff95dbd85d9f0b7655074 Mon Sep 17 00:00:00 2001
From: Gary Guo <gary@garyguo.net>
Date: Sun, 31 Oct 2021 17:57:32 +0000
Subject: [PATCH 2/2] Require `panic` and `panic_bounds_check` to be
 non-generic

---
 compiler/rustc_hir/src/lang_items.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/compiler/rustc_hir/src/lang_items.rs b/compiler/rustc_hir/src/lang_items.rs
index 97d4123138e..3037996d48b 100644
--- a/compiler/rustc_hir/src/lang_items.rs
+++ b/compiler/rustc_hir/src/lang_items.rs
@@ -281,12 +281,12 @@ language_item_table! {
     // in the sense that a crate is not required to have it defined to use it, but a final product
     // is required to define it somewhere. Additionally, there are restrictions on crates that use
     // a weak lang item, but do not have it defined.
-    Panic,                   sym::panic,               panic_fn,                   Target::Fn,             GenericRequirement::None;
+    Panic,                   sym::panic,               panic_fn,                   Target::Fn,             GenericRequirement::Exact(0);
     PanicFmt,                sym::panic_fmt,           panic_fmt,                  Target::Fn,             GenericRequirement::None;
     PanicDisplay,            sym::panic_display,       panic_display,              Target::Fn,             GenericRequirement::None;
     PanicStr,                sym::panic_str,           panic_str,                  Target::Fn,             GenericRequirement::None;
     ConstPanicFmt,           sym::const_panic_fmt,     const_panic_fmt,            Target::Fn,             GenericRequirement::None;
-    PanicBoundsCheck,        sym::panic_bounds_check,  panic_bounds_check_fn,      Target::Fn,             GenericRequirement::None;
+    PanicBoundsCheck,        sym::panic_bounds_check,  panic_bounds_check_fn,      Target::Fn,             GenericRequirement::Exact(0);
     PanicInfo,               sym::panic_info,          panic_info,                 Target::Struct,         GenericRequirement::None;
     PanicLocation,           sym::panic_location,      panic_location,             Target::Struct,         GenericRequirement::None;
     PanicImpl,               sym::panic_impl,          panic_impl,                 Target::Fn,             GenericRequirement::None;