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return 0 from Run when it doesn't specify a return value (#7180)

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https://carbon.compiler-explorer.com/z/88K9Kh5Wo shows the program
exiting with a garbage value copied from uninitialized memory.

This PR modifies `lower` to detect if the function lowered is the
entry point and doesn't specify a return type. If so, it emits
different LLVM IR to return int32 0, and modifies the lowered
function signature to match the int32 return type.
This commit is contained in:
Lucile Rose Nihlen
2026-05-08 19:00:47 +00:00
committed by GitHub
parent 3e36f7d43c
commit bc1ae703c3
22 changed files with 618 additions and 444 deletions
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toolchain/lower/testdata/interop/cpp/cpp_run.carbon
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+7 -6
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@@ -34,10 +34,10 @@ fn Run() {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define void @main() #1 !dbg !11 {
// CHECK:STDOUT: define i32 @main() #1 !dbg !11 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: call void @_ZN1N3RunEv(), !dbg !14
// CHECK:STDOUT: ret void, !dbg !15
// CHECK:STDOUT: call void @_ZN1N3RunEv(), !dbg !15
// CHECK:STDOUT: ret i32 0, !dbg !16
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: attributes #0 = { mustprogress nounwind uwtable "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
@@ -60,6 +60,7 @@ fn Run() {
// CHECK:STDOUT: !10 = !{!"Simple C++ TBAA"}
// CHECK:STDOUT: !11 = distinct !DISubprogram(name: "Run", linkageName: "main", scope: null, file: !6, line: 8, type: !12, spFlags: DISPFlagDefinition, unit: !5)
// CHECK:STDOUT: !12 = !DISubroutineType(types: !13)
// CHECK:STDOUT: !13 = !{null}
// CHECK:STDOUT: !14 = !DILocation(line: 9, column: 3, scope: !11)
// CHECK:STDOUT: !15 = !DILocation(line: 8, column: 1, scope: !11)
// CHECK:STDOUT: !13 = !{!14}
// CHECK:STDOUT: !14 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
// CHECK:STDOUT: !15 = !DILocation(line: 9, column: 3, scope: !11)
// CHECK:STDOUT: !16 = !DILocation(line: 8, column: 1, scope: !11)