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Rework handling of C++ references. (#6268)

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For now, map C++ reference types to const-qualified Carbon pointer types
rather than picking between a (non-const) pointer or a value type. This
fixes misbehavior in lowering for reference members in classes and
reference return types.

Update the special-case handling for references as function parameters
so that it continues to map const reference parameters to Carbon
pass-by-value, and unify the code paths for `self` parameters and other
parameters, which were mostly doing the same thing but had some subtle
differences.

Add references to the list of types that we can pass to and from C++
directly, without needing an additional layer of thunks.
This commit is contained in:
Richard Smith
2025-10-28 00:33:26 +00:00
committed by GitHub
parent 33166ffc7a
commit 6011040481
17 changed files with 845 additions and 437 deletions
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toolchain/lower/testdata/interop/cpp/method.carbon
Vendored
+5 -4
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@@ -90,11 +90,11 @@ fn Call(n: Cpp.NeedThunk) {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline mustprogress
// CHECK:STDOUT: define dso_local i32 @_ZNK1A6by_valEv.carbon_thunk(ptr %this) #0 {
// CHECK:STDOUT: define dso_local i32 @_ZNK1A6by_valEv.carbon_thunk(ptr nonnull align 8 dereferenceable(12) %this) #0 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %this.addr = alloca ptr, align 8
// CHECK:STDOUT: store ptr %this, ptr %this.addr, align 8
// CHECK:STDOUT: %0 = load ptr, ptr %this.addr, align 8
// CHECK:STDOUT: %0 = load ptr, ptr %this.addr, align 8, !nonnull !9, !align !12
// CHECK:STDOUT: %call = call i32 @_ZNK1A6by_valEv(ptr nonnull align 8 dereferenceable(12) %0)
// CHECK:STDOUT: ret i32 %call
// CHECK:STDOUT: }
@@ -128,6 +128,7 @@ fn Call(n: Cpp.NeedThunk) {
// CHECK:STDOUT: !9 = !{}
// CHECK:STDOUT: !10 = !DILocation(line: 7, column: 10, scope: !7)
// CHECK:STDOUT: !11 = !DILocation(line: 7, column: 3, scope: !7)
// CHECK:STDOUT: !12 = !{i64 8}
// CHECK:STDOUT: ; ModuleID = 'call_by_ref.carbon'
// CHECK:STDOUT: source_filename = "call_by_ref.carbon"
// CHECK:STDOUT: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
@@ -235,13 +236,13 @@ fn Call(n: Cpp.NeedThunk) {
// CHECK:STDOUT: declare void @llvm.lifetime.start.p0(ptr captures(none)) #0
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline mustprogress
// CHECK:STDOUT: define dso_local void @_ZNK9NeedThunk8ImplicitEa.carbon_thunk(ptr %this, ptr %c) #1 {
// CHECK:STDOUT: define dso_local void @_ZNK9NeedThunk8ImplicitEa.carbon_thunk(ptr nonnull align 1 dereferenceable(1) %this, ptr %c) #1 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %this.addr = alloca ptr, align 8
// CHECK:STDOUT: %c.addr = alloca ptr, align 8
// CHECK:STDOUT: store ptr %this, ptr %this.addr, align 8
// CHECK:STDOUT: store ptr %c, ptr %c.addr, align 8
// CHECK:STDOUT: %0 = load ptr, ptr %this.addr, align 8
// CHECK:STDOUT: %0 = load ptr, ptr %this.addr, align 8, !nonnull !9
// CHECK:STDOUT: %1 = load ptr, ptr %c.addr, align 8
// CHECK:STDOUT: %2 = load i8, ptr %1, align 1
// CHECK:STDOUT: call void @_ZNK9NeedThunk8ImplicitEa(ptr nonnull align 1 dereferenceable(1) %0, i8 signext %2)