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Give thunks weak_odr linkage. (#7525)

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We can end up emitting the same thunk from multiple compilations in some
cases -- in particular, when the thunk is wrapping a function that is
either synthesized by the compiler or imported from C++. When this
happens, we will have multiple-definition link errors unless we allow
redefinitions across multiple files.

It'd be nice to detect when we need to do this and when we don't, but
that's a bit tricky to do in practice. Ideally, in fact, we would use a
different strategy, and emit the thunks as discardable definitions in
each compilation that *uses* them. But for now emitting them with
weak_odr linkage seems like a good way to make progress.
This commit is contained in:
Richard Smith
2026-07-17 13:25:19 +00:00
committed by GitHub
parent 643ab57f5a
commit 5c544f7c2f
20 changed files with 362 additions and 75 deletions
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toolchain/lower/testdata/interop/cpp/enum.carbon
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+6 -6
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@@ -579,7 +579,7 @@ fn CallCompareGeneric3(a: Cpp.C.E, b: Cpp.ConvertToEnum2) -> bool {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define i1 @"_CEqual:thunk:EqWith.83b9626e83cf3dcc.Core:enclosed"(i16 %self, ptr %other) #2 !dbg !55 {
// CHECK:STDOUT: define weak_odr i1 @"_CEqual:thunk:EqWith.83b9626e83cf3dcc.Core:enclosed"(i16 %self, ptr %other) #2 !dbg !55 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %.4.temp = alloca i16, align 2, !dbg !59
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.4.temp), !dbg !59
@@ -590,7 +590,7 @@ fn CallCompareGeneric3(a: Cpp.C.E, b: Cpp.ConvertToEnum2) -> bool {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define i1 @"_CNotEqual:thunk:EqWith.83b9626e83cf3dcc.Core:enclosed"(i16 %self, ptr %other) #2 !dbg !60 {
// CHECK:STDOUT: define weak_odr i1 @"_CNotEqual:thunk:EqWith.83b9626e83cf3dcc.Core:enclosed"(i16 %self, ptr %other) #2 !dbg !60 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %.4.temp = alloca i16, align 2, !dbg !64
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.4.temp), !dbg !64
@@ -608,7 +608,7 @@ fn CallCompareGeneric3(a: Cpp.C.E, b: Cpp.ConvertToEnum2) -> bool {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define i1 @"_CEqual:thunk:EqWith.e8fe48de943d9652.Core:enclosed"(i32 %self, ptr %other) #2 !dbg !71 {
// CHECK:STDOUT: define weak_odr i1 @"_CEqual:thunk:EqWith.e8fe48de943d9652.Core:enclosed"(i32 %self, ptr %other) #2 !dbg !71 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %__carbon_thunk.call = call i32 @_ZNK13ConvertToEnumcv2E2Ev.carbon_thunk._(ptr %other), !dbg !75
// CHECK:STDOUT: %Equal.call = icmp eq i32 %self, %__carbon_thunk.call, !dbg !75
@@ -616,7 +616,7 @@ fn CallCompareGeneric3(a: Cpp.C.E, b: Cpp.ConvertToEnum2) -> bool {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define i1 @"_CNotEqual:thunk:EqWith.e8fe48de943d9652.Core:enclosed"(i32 %self, ptr %other) #2 !dbg !76 {
// CHECK:STDOUT: define weak_odr i1 @"_CNotEqual:thunk:EqWith.e8fe48de943d9652.Core:enclosed"(i32 %self, ptr %other) #2 !dbg !76 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %__carbon_thunk.call = call i32 @_ZNK13ConvertToEnumcv2E2Ev.carbon_thunk._(ptr %other), !dbg !80
// CHECK:STDOUT: %NotEqual.call = icmp ne i32 %self, %__carbon_thunk.call, !dbg !80
@@ -631,7 +631,7 @@ fn CallCompareGeneric3(a: Cpp.C.E, b: Cpp.ConvertToEnum2) -> bool {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define i1 @"_CEqual:thunk:EqWith.a294139a6615e163.Core:enclosed"(i16 %self, ptr %other) #2 !dbg !87 {
// CHECK:STDOUT: define weak_odr i1 @"_CEqual:thunk:EqWith.a294139a6615e163.Core:enclosed"(i16 %self, ptr %other) #2 !dbg !87 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %.4.temp = alloca i16, align 2, !dbg !91
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.4.temp), !dbg !91
@@ -642,7 +642,7 @@ fn CallCompareGeneric3(a: Cpp.C.E, b: Cpp.ConvertToEnum2) -> bool {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define i1 @"_CNotEqual:thunk:EqWith.a294139a6615e163.Core:enclosed"(i16 %self, ptr %other) #2 !dbg !92 {
// CHECK:STDOUT: define weak_odr i1 @"_CNotEqual:thunk:EqWith.a294139a6615e163.Core:enclosed"(i16 %self, ptr %other) #2 !dbg !92 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %.4.temp = alloca i16, align 2, !dbg !96
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.4.temp), !dbg !96