Don't use a 1-to-1 mapping between mir local and cranelift_frontend variable

src/abi/comments.rs

@@ -2,6 +2,8 @@ use std::borrow::Cow;
 
 use rustc_middle::mir;
 
+use cranelift_codegen::entity::EntityRef;
+
 use crate::abi::pass_mode::*;
 use crate::prelude::*;
 
@@ -72,9 +74,9 @@ pub(super) fn add_local_place_comments<'tcx>(
     } = layout;
 
     let (kind, extra) = match *place.inner() {
-        CPlaceInner::Var(var) => {
-            assert_eq!(local, var);
-            ("ssa", std::borrow::Cow::Borrowed(""))
+        CPlaceInner::Var(place_local, var) => {
+            assert_eq!(local, place_local);
+            ("ssa", Cow::Owned(format!(",var={}", var.index())))
         }
         CPlaceInner::Addr(ptr, meta) => {
             let meta = if let Some(meta) = meta {

src/base.rs

@@ -51,6 +51,7 @@ pub(crate) fn trans_fn<'tcx, B: Backend + 'static>(
         constants_cx: &mut cx.constants_cx,
         vtables: &mut cx.vtables,
         source_info_set: indexmap::IndexSet::new(),
+        next_ssa_var: 0,
     };
 
     let arg_uninhabited = fx.mir.args_iter().any(|arg| fx.layout_of(fx.monomorphize(&fx.mir.local_decls[arg].ty)).abi.is_uninhabited());

src/common.rs

@@ -6,10 +6,6 @@ use cranelift_codegen::ir::{InstructionData, Opcode, ValueDef};
 
 use crate::prelude::*;
 
-pub(crate) fn mir_var(loc: Local) -> Variable {
-    Variable::with_u32(loc.index() as u32)
-}
-
 pub(crate) fn pointer_ty(tcx: TyCtxt<'_>) -> types::Type {
     match tcx.data_layout.pointer_size.bits() {
         16 => types::I16,
@@ -258,6 +254,9 @@ pub(crate) struct FunctionCx<'clif, 'tcx, B: Backend + 'static> {
     pub(crate) vtables: &'clif mut FxHashMap<(Ty<'tcx>, Option<ty::PolyExistentialTraitRef<'tcx>>), DataId>,
 
     pub(crate) source_info_set: indexmap::IndexSet<SourceInfo>,
+
+    /// This should only be accessed by `CPlace::new_var`.
+    pub(crate) next_ssa_var: u32,
 }
 
 impl<'tcx, B: Backend> LayoutOf for FunctionCx<'_, 'tcx, B> {

src/debuginfo/mod.rs

@@ -4,6 +4,7 @@ mod unwind;
 
 use crate::prelude::*;
 
+use cranelift_codegen::entity::EntityRef;
 use cranelift_codegen::ir::{StackSlots, ValueLabel, ValueLoc};
 use cranelift_codegen::isa::TargetIsa;
 use cranelift_codegen::ValueLocRange;
@@ -376,8 +377,8 @@ fn place_location<'tcx>(
     assert!(place.projection.is_empty()); // FIXME implement them
 
     match local_map[&place.local].inner() {
-        CPlaceInner::Var(local) => {
-            let value_label = cranelift_codegen::ir::ValueLabel::from_u32(local.as_u32());
+        CPlaceInner::Var(_local, var) => {
+            let value_label = cranelift_codegen::ir::ValueLabel::new(var.index());
             if let Some(value_loc_ranges) = value_labels_ranges.get(&value_label) {
                 let loc_list = LocationList(
                     value_loc_ranges

src/value_and_place.rs

@@ -1,5 +1,6 @@
 use crate::prelude::*;
 
+use cranelift_codegen::entity::EntityRef;
 use cranelift_codegen::ir::immediates::Offset32;
 
 fn codegen_field<'tcx>(
@@ -256,7 +257,7 @@ pub(crate) struct CPlace<'tcx> {
 
 #[derive(Debug, Copy, Clone)]
 pub(crate) enum CPlaceInner {
-    Var(Local),
+    Var(Local, Variable),
     Addr(Pointer, Option<Value>),
 }
 
@@ -301,10 +302,12 @@ impl<'tcx> CPlace<'tcx> {
         local: Local,
         layout: TyAndLayout<'tcx>,
     ) -> CPlace<'tcx> {
+        let var = Variable::with_u32(fx.next_ssa_var);
+        fx.next_ssa_var += 1;
         fx.bcx
-            .declare_var(mir_var(local), fx.clif_type(layout.ty).unwrap());
+            .declare_var(var, fx.clif_type(layout.ty).unwrap());
         CPlace {
-            inner: CPlaceInner::Var(local),
+            inner: CPlaceInner::Var(local, var),
             layout,
         }
     }
@@ -326,9 +329,9 @@ impl<'tcx> CPlace<'tcx> {
     pub(crate) fn to_cvalue(self, fx: &mut FunctionCx<'_, 'tcx, impl Backend>) -> CValue<'tcx> {
         let layout = self.layout();
         match self.inner {
-            CPlaceInner::Var(var) => {
-                let val = fx.bcx.use_var(mir_var(var));
-                fx.bcx.set_val_label(val, cranelift_codegen::ir::ValueLabel::from_u32(var.as_u32()));
+            CPlaceInner::Var(_local, var) => {
+                let val = fx.bcx.use_var(var);
+                fx.bcx.set_val_label(val, cranelift_codegen::ir::ValueLabel::new(var.index()));
                 CValue::by_val(val, layout)
             }
             CPlaceInner::Addr(ptr, extra) => {
@@ -351,7 +354,7 @@ impl<'tcx> CPlace<'tcx> {
     pub(crate) fn to_ptr_maybe_unsized(self) -> (Pointer, Option<Value>) {
         match self.inner {
             CPlaceInner::Addr(ptr, extra) => (ptr, extra),
-            CPlaceInner::Var(_) => bug!("Expected CPlace::Addr, found {:?}", self),
+            CPlaceInner::Var(_, _) => bug!("Expected CPlace::Addr, found {:?}", self),
         }
     }
 
@@ -442,7 +445,7 @@ impl<'tcx> CPlace<'tcx> {
 
         let dst_layout = self.layout();
         let to_ptr = match self.inner {
-            CPlaceInner::Var(var) => {
+            CPlaceInner::Var(_local, var) => {
                 let data = CValue(from.0, dst_layout).load_scalar(fx);
                 let src_ty = fx.bcx.func.dfg.value_type(data);
                 let dst_ty = fx.clif_type(self.layout().ty).unwrap();
@@ -459,8 +462,8 @@ impl<'tcx> CPlace<'tcx> {
                     }
                     _ => unreachable!("write_cvalue_transmute: {:?} -> {:?}", src_ty, dst_ty),
                 };
-                fx.bcx.set_val_label(data, cranelift_codegen::ir::ValueLabel::from_u32(var.as_u32()));
-                fx.bcx.def_var(mir_var(var), data);
+                fx.bcx.set_val_label(data, cranelift_codegen::ir::ValueLabel::new(var.index()));
+                fx.bcx.def_var(var, data);
                 return;
             }
             CPlaceInner::Addr(ptr, None) => {