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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/reference.carbon
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+2 -2
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@@ -177,7 +177,7 @@ fn GetRefs() {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define void @"_COp:thunk:Default.dc3dd9c349162a91.Core:C.Cpp"(ptr sret({}) %return) #2 !dbg !30 {
// CHECK:STDOUT: define weak_odr void @"_COp:thunk:Default.dc3dd9c349162a91.Core:C.Cpp"(ptr sret({}) %return) #2 !dbg !30 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: call void @_ZN1CC1Ev.carbon_thunk.(ptr %return), !dbg !34
// CHECK:STDOUT: ret void, !dbg !34
@@ -368,7 +368,7 @@ fn GetRefs() {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define void @"_COp:thunk:Default.dc3dd9c349162a91.Core:C.Cpp"(ptr sret({}) %return) #2 !dbg !30 {
// CHECK:STDOUT: define weak_odr void @"_COp:thunk:Default.dc3dd9c349162a91.Core:C.Cpp"(ptr sret({}) %return) #2 !dbg !30 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: call void @_ZN1CC1Ev.carbon_thunk.(ptr %return), !dbg !34
// CHECK:STDOUT: ret void, !dbg !34