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Unify "needs thunk" logic. (#6277)

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Remove duplication between determining whether a parameter needs custom
thunk mapping and whether a function needs a thunk. Now a function needs
a thunk if any parameter or the return type does.

This fixes some inconsistencies; previously:
- We would not require a thunk when passing an `unsigned int`, but if we
  had a thunk we'd pass `unsigned int` indirectly.
- We would always require a thunk for an enum parameter, even though
  we'd actually pass it directly if its underlying type is a 32- or
  64-bit integer.
- We would require a thunk for a nullable pointer, even though
  we arrange for all pointer types to have the same ABI in Carbon and
  C++, including nullable pointers / Optional(T*).

This also causes us to use a thunk for rvalue reference return types,
which we used to miscompile.

Depends on #6276.
This commit is contained in:
Richard Smith
2025-10-27 22:49:29 +00:00
committed by GitHub
parent f022e91e45
commit a1a35c207e
7 changed files with 181 additions and 229 deletions
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toolchain/lower/testdata/interop/cpp/parameters.carbon
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+46 -56
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@@ -121,49 +121,43 @@ fn PassValueExpr(y: Cpp.Y) {
// CHECK:STDOUT: %.loc7_22.3.temp = alloca i16, align 2, !dbg !11
// CHECK:STDOUT: %.loc9_21.3.temp = alloca i8, align 1, !dbg !12
// CHECK:STDOUT: %.loc9_24.3.temp = alloca i16, align 2, !dbg !13
// CHECK:STDOUT: %.loc9_27.3.temp = alloca i32, align 4, !dbg !14
// CHECK:STDOUT: %.loc9_30.3.temp = alloca i64, align 8, !dbg !15
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.loc7_19.3.temp), !dbg !10
// CHECK:STDOUT: store i8 1, ptr %.loc7_19.3.temp, align 1, !dbg !10
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.loc7_22.3.temp), !dbg !11
// CHECK:STDOUT: store i16 2, ptr %.loc7_22.3.temp, align 2, !dbg !11
// CHECK:STDOUT: call void @_Z11pass_signedasil.carbon_thunk(ptr %.loc7_19.3.temp, ptr %.loc7_22.3.temp, i32 3, i64 4), !dbg !16
// CHECK:STDOUT: call void @_Z11pass_signedasil.carbon_thunk(ptr %.loc7_19.3.temp, ptr %.loc7_22.3.temp, i32 3, i64 4), !dbg !14
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.loc9_21.3.temp), !dbg !12
// CHECK:STDOUT: store i8 1, ptr %.loc9_21.3.temp, align 1, !dbg !12
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.loc9_24.3.temp), !dbg !13
// CHECK:STDOUT: store i16 2, ptr %.loc9_24.3.temp, align 2, !dbg !13
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.loc9_27.3.temp), !dbg !14
// CHECK:STDOUT: store i32 3, ptr %.loc9_27.3.temp, align 4, !dbg !14
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.loc9_30.3.temp), !dbg !15
// CHECK:STDOUT: store i64 4, ptr %.loc9_30.3.temp, align 4, !dbg !15
// CHECK:STDOUT: call void @_Z13pass_unsignedhtjm.carbon_thunk(ptr %.loc9_21.3.temp, ptr %.loc9_24.3.temp, ptr %.loc9_27.3.temp, ptr %.loc9_30.3.temp), !dbg !17
// CHECK:STDOUT: ret void, !dbg !18
// CHECK:STDOUT: call void @_Z13pass_unsignedhtjm.carbon_thunk(ptr %.loc9_21.3.temp, ptr %.loc9_24.3.temp, i32 3, i64 4), !dbg !15
// CHECK:STDOUT: ret void, !dbg !16
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: declare i16 @_CMakeShort.Main()
// CHECK:STDOUT:
// CHECK:STDOUT: define void @_CPassShort.Main(i16 %a, ptr %b) !dbg !19 {
// CHECK:STDOUT: define void @_CPassShort.Main(i16 %a, ptr %b) !dbg !17 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %.loc17_18.1.temp = alloca i16, align 2, !dbg !20
// CHECK:STDOUT: %.loc18_18.3.temp = alloca i16, align 2, !dbg !21
// CHECK:STDOUT: %.loc19_18.2.temp = alloca i16, align 2, !dbg !22
// CHECK:STDOUT: %.loc20_28.3.temp = alloca i16, align 2, !dbg !23
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.loc17_18.1.temp), !dbg !20
// CHECK:STDOUT: store i16 %a, ptr %.loc17_18.1.temp, align 2, !dbg !20
// CHECK:STDOUT: call void @_Z10pass_shorts.carbon_thunk(ptr %.loc17_18.1.temp), !dbg !24
// CHECK:STDOUT: %.loc18_18.2 = load i16, ptr %b, align 2, !dbg !21
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.loc18_18.3.temp), !dbg !21
// CHECK:STDOUT: store i16 %.loc18_18.2, ptr %.loc18_18.3.temp, align 2, !dbg !21
// CHECK:STDOUT: call void @_Z10pass_shorts.carbon_thunk(ptr %.loc18_18.3.temp), !dbg !25
// CHECK:STDOUT: %.loc19_18.1 = load i16, ptr @_Cc.Main, align 2, !dbg !22
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.loc19_18.2.temp), !dbg !22
// CHECK:STDOUT: store i16 %.loc19_18.1, ptr %.loc19_18.2.temp, align 2, !dbg !22
// CHECK:STDOUT: call void @_Z10pass_shorts.carbon_thunk(ptr %.loc19_18.2.temp), !dbg !26
// CHECK:STDOUT: %MakeShort.call = call i16 @_CMakeShort.Main(), !dbg !23
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.loc20_28.3.temp), !dbg !23
// CHECK:STDOUT: store i16 %MakeShort.call, ptr %.loc20_28.3.temp, align 2, !dbg !23
// CHECK:STDOUT: call void @_Z10pass_shorts.carbon_thunk(ptr %.loc20_28.3.temp), !dbg !27
// CHECK:STDOUT: ret void, !dbg !28
// CHECK:STDOUT: %.loc17_18.1.temp = alloca i16, align 2, !dbg !18
// CHECK:STDOUT: %.loc18_18.3.temp = alloca i16, align 2, !dbg !19
// CHECK:STDOUT: %.loc19_18.2.temp = alloca i16, align 2, !dbg !20
// CHECK:STDOUT: %.loc20_28.3.temp = alloca i16, align 2, !dbg !21
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.loc17_18.1.temp), !dbg !18
// CHECK:STDOUT: store i16 %a, ptr %.loc17_18.1.temp, align 2, !dbg !18
// CHECK:STDOUT: call void @_Z10pass_shorts.carbon_thunk(ptr %.loc17_18.1.temp), !dbg !22
// CHECK:STDOUT: %.loc18_18.2 = load i16, ptr %b, align 2, !dbg !19
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.loc18_18.3.temp), !dbg !19
// CHECK:STDOUT: store i16 %.loc18_18.2, ptr %.loc18_18.3.temp, align 2, !dbg !19
// CHECK:STDOUT: call void @_Z10pass_shorts.carbon_thunk(ptr %.loc18_18.3.temp), !dbg !23
// CHECK:STDOUT: %.loc19_18.1 = load i16, ptr @_Cc.Main, align 2, !dbg !20
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.loc19_18.2.temp), !dbg !20
// CHECK:STDOUT: store i16 %.loc19_18.1, ptr %.loc19_18.2.temp, align 2, !dbg !20
// CHECK:STDOUT: call void @_Z10pass_shorts.carbon_thunk(ptr %.loc19_18.2.temp), !dbg !24
// CHECK:STDOUT: %MakeShort.call = call i16 @_CMakeShort.Main(), !dbg !21
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.loc20_28.3.temp), !dbg !21
// CHECK:STDOUT: store i16 %MakeShort.call, ptr %.loc20_28.3.temp, align 2, !dbg !21
// CHECK:STDOUT: call void @_Z10pass_shorts.carbon_thunk(ptr %.loc20_28.3.temp), !dbg !25
// CHECK:STDOUT: ret void, !dbg !26
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: readwrite)
@@ -193,25 +187,23 @@ fn PassValueExpr(y: Cpp.Y) {
// CHECK:STDOUT: declare void @_Z11pass_signedasil(i8 signext, i16 signext, i32, i64) #2
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline mustprogress
// CHECK:STDOUT: define dso_local void @_Z13pass_unsignedhtjm.carbon_thunk(ptr %0, ptr %1, ptr %2, ptr %3) #1 {
// CHECK:STDOUT: define dso_local void @_Z13pass_unsignedhtjm.carbon_thunk(ptr %0, ptr %1, i32 %2, i64 %3) #1 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %.addr = alloca ptr, align 8
// CHECK:STDOUT: %.addr1 = alloca ptr, align 8
// CHECK:STDOUT: %.addr2 = alloca ptr, align 8
// CHECK:STDOUT: %.addr3 = alloca ptr, align 8
// CHECK:STDOUT: %.addr2 = alloca i32, align 4
// CHECK:STDOUT: %.addr3 = alloca i64, align 8
// CHECK:STDOUT: store ptr %0, ptr %.addr, align 8
// CHECK:STDOUT: store ptr %1, ptr %.addr1, align 8
// CHECK:STDOUT: store ptr %2, ptr %.addr2, align 8
// CHECK:STDOUT: store ptr %3, ptr %.addr3, align 8
// CHECK:STDOUT: store i32 %2, ptr %.addr2, align 4
// CHECK:STDOUT: store i64 %3, ptr %.addr3, align 8
// CHECK:STDOUT: %4 = load ptr, ptr %.addr, align 8
// CHECK:STDOUT: %5 = load i8, ptr %4, align 1
// CHECK:STDOUT: %6 = load ptr, ptr %.addr1, align 8
// CHECK:STDOUT: %7 = load i16, ptr %6, align 2
// CHECK:STDOUT: %8 = load ptr, ptr %.addr2, align 8
// CHECK:STDOUT: %9 = load i32, ptr %8, align 4
// CHECK:STDOUT: %10 = load ptr, ptr %.addr3, align 8
// CHECK:STDOUT: %11 = load i64, ptr %10, align 8
// CHECK:STDOUT: call void @_Z13pass_unsignedhtjm(i8 zeroext %5, i16 zeroext %7, i32 %9, i64 %11)
// CHECK:STDOUT: %8 = load i32, ptr %.addr2, align 4
// CHECK:STDOUT: %9 = load i64, ptr %.addr3, align 8
// CHECK:STDOUT: call void @_Z13pass_unsignedhtjm(i8 zeroext %5, i16 zeroext %7, i32 %8, i64 %9)
// CHECK:STDOUT: ret void
// CHECK:STDOUT: }
// CHECK:STDOUT:
@@ -231,7 +223,7 @@ fn PassValueExpr(y: Cpp.Y) {
// CHECK:STDOUT: declare void @_Z10pass_shorts(i16 signext) #2
// CHECK:STDOUT:
// CHECK:STDOUT: ; uselistorder directives
// CHECK:STDOUT: uselistorder ptr @llvm.lifetime.start.p0, { 9, 8, 7, 6, 5, 4, 3, 2, 1, 0 }
// CHECK:STDOUT: uselistorder ptr @llvm.lifetime.start.p0, { 7, 6, 5, 4, 3, 2, 1, 0 }
// CHECK:STDOUT:
// CHECK:STDOUT: attributes #0 = { nocallback nofree nosync nounwind willreturn memory(argmem: readwrite) }
// CHECK:STDOUT: attributes #1 = { alwaysinline mustprogress "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="0" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
@@ -254,21 +246,19 @@ fn PassValueExpr(y: Cpp.Y) {
// CHECK:STDOUT: !11 = !DILocation(line: 7, column: 22, scope: !7)
// CHECK:STDOUT: !12 = !DILocation(line: 9, column: 21, scope: !7)
// CHECK:STDOUT: !13 = !DILocation(line: 9, column: 24, scope: !7)
// CHECK:STDOUT: !14 = !DILocation(line: 9, column: 27, scope: !7)
// CHECK:STDOUT: !15 = !DILocation(line: 9, column: 30, scope: !7)
// CHECK:STDOUT: !16 = !DILocation(line: 7, column: 3, scope: !7)
// CHECK:STDOUT: !17 = !DILocation(line: 9, column: 3, scope: !7)
// CHECK:STDOUT: !18 = !DILocation(line: 6, column: 1, scope: !7)
// CHECK:STDOUT: !19 = distinct !DISubprogram(name: "PassShort", linkageName: "_CPassShort.Main", scope: null, file: !6, line: 16, type: !8, spFlags: DISPFlagDefinition, unit: !5)
// CHECK:STDOUT: !20 = !DILocation(line: 17, column: 18, scope: !19)
// CHECK:STDOUT: !21 = !DILocation(line: 18, column: 18, scope: !19)
// CHECK:STDOUT: !22 = !DILocation(line: 19, column: 18, scope: !19)
// CHECK:STDOUT: !23 = !DILocation(line: 20, column: 18, scope: !19)
// CHECK:STDOUT: !24 = !DILocation(line: 17, column: 3, scope: !19)
// CHECK:STDOUT: !25 = !DILocation(line: 18, column: 3, scope: !19)
// CHECK:STDOUT: !26 = !DILocation(line: 19, column: 3, scope: !19)
// CHECK:STDOUT: !27 = !DILocation(line: 20, column: 3, scope: !19)
// CHECK:STDOUT: !28 = !DILocation(line: 16, column: 1, scope: !19)
// CHECK:STDOUT: !14 = !DILocation(line: 7, column: 3, scope: !7)
// CHECK:STDOUT: !15 = !DILocation(line: 9, column: 3, scope: !7)
// CHECK:STDOUT: !16 = !DILocation(line: 6, column: 1, scope: !7)
// CHECK:STDOUT: !17 = distinct !DISubprogram(name: "PassShort", linkageName: "_CPassShort.Main", scope: null, file: !6, line: 16, type: !8, spFlags: DISPFlagDefinition, unit: !5)
// CHECK:STDOUT: !18 = !DILocation(line: 17, column: 18, scope: !17)
// CHECK:STDOUT: !19 = !DILocation(line: 18, column: 18, scope: !17)
// CHECK:STDOUT: !20 = !DILocation(line: 19, column: 18, scope: !17)
// CHECK:STDOUT: !21 = !DILocation(line: 20, column: 18, scope: !17)
// CHECK:STDOUT: !22 = !DILocation(line: 17, column: 3, scope: !17)
// CHECK:STDOUT: !23 = !DILocation(line: 18, column: 3, scope: !17)
// CHECK:STDOUT: !24 = !DILocation(line: 19, column: 3, scope: !17)
// CHECK:STDOUT: !25 = !DILocation(line: 20, column: 3, scope: !17)
// CHECK:STDOUT: !26 = !DILocation(line: 16, column: 1, scope: !17)
// CHECK:STDOUT: ; ModuleID = 'import_struct.carbon'
// CHECK:STDOUT: source_filename = "import_struct.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"