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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/thunks.carbon
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+6 -6
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@@ -128,14 +128,14 @@ fn Call(a: Cpp.Collide, b: Cpp.AnonCollide) {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define void @"_COp:thunk:Copy.60e3c6e2415a2ad6.Core:NeedThunk.Cpp"(ptr sret([1 x i8]) %return, ptr %self) #2 !dbg !24 {
// CHECK:STDOUT: define weak_odr void @"_COp:thunk:Copy.60e3c6e2415a2ad6.Core:NeedThunk.Cpp"(ptr sret([1 x i8]) %return, ptr %self) #2 !dbg !24 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: call void @_ZN9NeedThunkC1ERKS_.carbon_thunk._(ptr %self, ptr %return), !dbg !30
// CHECK:STDOUT: ret void, !dbg !30
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define void @"_COp:thunk:Destroy.092ad14c7174f642.Core:NeedThunk.Cpp"(ptr %self) #2 !dbg !31 {
// CHECK:STDOUT: define weak_odr void @"_COp:thunk:Destroy.092ad14c7174f642.Core:NeedThunk.Cpp"(ptr %self) #2 !dbg !31 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: ret void, !dbg !34
// CHECK:STDOUT: }
@@ -232,7 +232,7 @@ fn Call(a: Cpp.Collide, b: Cpp.AnonCollide) {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define void @"_COp:thunk:Copy.c0735c73762b4d1c.Core:Box.Cpp"(ptr sret([1 x i8]) %return, ptr %self) #2 !dbg !27 {
// CHECK:STDOUT: define weak_odr void @"_COp:thunk:Copy.c0735c73762b4d1c.Core:Box.Cpp"(ptr sret([1 x i8]) %return, ptr %self) #2 !dbg !27 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: call void @_ZN3BoxI1AEC1ERKS1_.carbon_thunk._(ptr %self, ptr %return), !dbg !33
// CHECK:STDOUT: ret void, !dbg !33
@@ -252,7 +252,7 @@ fn Call(a: Cpp.Collide, b: Cpp.AnonCollide) {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define void @"_COp:thunk:Copy.2c1dd62357f2b914.Core:Box.Cpp"(ptr sret([1 x i8]) %return, ptr %self) #2 !dbg !36 {
// CHECK:STDOUT: define weak_odr void @"_COp:thunk:Copy.2c1dd62357f2b914.Core:Box.Cpp"(ptr sret([1 x i8]) %return, ptr %self) #2 !dbg !36 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: call void @_ZN3BoxI1BEC1ERKS1_.carbon_thunk._(ptr %self, ptr %return), !dbg !39
// CHECK:STDOUT: ret void, !dbg !39
@@ -368,7 +368,7 @@ fn Call(a: Cpp.Collide, b: Cpp.AnonCollide) {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define void @"_COp:thunk:Copy.9e522bb4dbf82e5c.Core:Collide.Cpp"(ptr sret([1 x i8]) %return, ptr %self) #2 !dbg !27 {
// CHECK:STDOUT: define weak_odr void @"_COp:thunk:Copy.9e522bb4dbf82e5c.Core:Collide.Cpp"(ptr sret([1 x i8]) %return, ptr %self) #2 !dbg !27 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: call void @_ZN7CollideC1ERKS_.carbon_thunk._(ptr %self, ptr %return), !dbg !33
// CHECK:STDOUT: ret void, !dbg !33
@@ -388,7 +388,7 @@ fn Call(a: Cpp.Collide, b: Cpp.AnonCollide) {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define void @"_COp:thunk:Copy.d1fe27f3241437fa.Core:Collide..Cpp"(ptr sret([1 x i8]) %return, ptr %self) #2 !dbg !36 {
// CHECK:STDOUT: define weak_odr void @"_COp:thunk:Copy.d1fe27f3241437fa.Core:Collide..Cpp"(ptr sret([1 x i8]) %return, ptr %self) #2 !dbg !36 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: call void @_ZN12_GLOBAL__N_17CollideC1ERKS0_.carbon_thunk._(ptr %self, ptr %return), !dbg !39
// CHECK:STDOUT: ret void, !dbg !39