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

Browse Source 
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/function/generic/call_different_impls.carbon
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+21 -18
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@@ -53,27 +53,27 @@ fn Run() {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define void @main() #0 !dbg !12 {
// CHECK:STDOUT: define i32 @main() #0 !dbg !12 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: call void @_CG.Main.e55c78367db83a6b(), !dbg !13
// CHECK:STDOUT: call void @_CG.Main.95a632fb0c368a62(), !dbg !14
// CHECK:STDOUT: ret void, !dbg !15
// CHECK:STDOUT: call void @_CG.Main.e55c78367db83a6b(), !dbg !16
// CHECK:STDOUT: call void @_CG.Main.95a632fb0c368a62(), !dbg !17
// CHECK:STDOUT: ret i32 0, !dbg !18
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: declare i32 @printf(ptr, ...)
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define linkonce_odr void @_CG.Main.e55c78367db83a6b() #0 !dbg !16 {
// CHECK:STDOUT: define linkonce_odr void @_CG.Main.e55c78367db83a6b() #0 !dbg !19 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: call void @"_CF.X.Main:I.Main"(), !dbg !17
// CHECK:STDOUT: ret void, !dbg !18
// CHECK:STDOUT: call void @"_CF.X.Main:I.Main"(), !dbg !20
// CHECK:STDOUT: ret void, !dbg !21
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define linkonce_odr void @_CG.Main.95a632fb0c368a62() #0 !dbg !19 {
// CHECK:STDOUT: define linkonce_odr void @_CG.Main.95a632fb0c368a62() #0 !dbg !22 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: call void @"_CF.Y.Main:I.Main"(), !dbg !20
// CHECK:STDOUT: ret void, !dbg !21
// CHECK:STDOUT: call void @"_CF.Y.Main:I.Main"(), !dbg !23
// CHECK:STDOUT: ret void, !dbg !24
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; uselistorder directives
@@ -96,13 +96,16 @@ fn Run() {
// CHECK:STDOUT: !9 = distinct !DISubprogram(name: "F", linkageName: "_CF.Y.Main:I.Main", scope: null, file: !3, line: 24, type: !5, spFlags: DISPFlagDefinition, unit: !2)
// CHECK:STDOUT: !10 = !DILocation(line: 24, column: 12, scope: !9)
// CHECK:STDOUT: !11 = !DILocation(line: 24, column: 3, scope: !9)
// CHECK:STDOUT: !12 = distinct !DISubprogram(name: "Run", linkageName: "main", scope: null, file: !3, line: 31, type: !5, spFlags: DISPFlagDefinition, unit: !2)
// CHECK:STDOUT: !13 = !DILocation(line: 32, column: 3, scope: !12)
// CHECK:STDOUT: !14 = !DILocation(line: 33, column: 3, scope: !12)
// CHECK:STDOUT: !15 = !DILocation(line: 31, column: 1, scope: !12)
// CHECK:STDOUT: !16 = distinct !DISubprogram(name: "G", linkageName: "_CG.Main.e55c78367db83a6b", scope: null, file: !3, line: 29, type: !5, spFlags: DISPFlagDefinition, unit: !2)
// CHECK:STDOUT: !17 = !DILocation(line: 29, column: 15, scope: !16)
// CHECK:STDOUT: !18 = !DILocation(line: 29, column: 1, scope: !16)
// CHECK:STDOUT: !19 = distinct !DISubprogram(name: "G", linkageName: "_CG.Main.95a632fb0c368a62", scope: null, file: !3, line: 29, type: !5, spFlags: DISPFlagDefinition, unit: !2)
// CHECK:STDOUT: !12 = distinct !DISubprogram(name: "Run", linkageName: "main", scope: null, file: !3, line: 31, type: !13, spFlags: DISPFlagDefinition, unit: !2)
// CHECK:STDOUT: !13 = !DISubroutineType(types: !14)
// CHECK:STDOUT: !14 = !{!15}
// CHECK:STDOUT: !15 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
// CHECK:STDOUT: !16 = !DILocation(line: 32, column: 3, scope: !12)
// CHECK:STDOUT: !17 = !DILocation(line: 33, column: 3, scope: !12)
// CHECK:STDOUT: !18 = !DILocation(line: 31, column: 1, scope: !12)
// CHECK:STDOUT: !19 = distinct !DISubprogram(name: "G", linkageName: "_CG.Main.e55c78367db83a6b", scope: null, file: !3, line: 29, type: !5, spFlags: DISPFlagDefinition, unit: !2)
// CHECK:STDOUT: !20 = !DILocation(line: 29, column: 15, scope: !19)
// CHECK:STDOUT: !21 = !DILocation(line: 29, column: 1, scope: !19)
// CHECK:STDOUT: !22 = distinct !DISubprogram(name: "G", linkageName: "_CG.Main.95a632fb0c368a62", scope: null, file: !3, line: 29, type: !5, spFlags: DISPFlagDefinition, unit: !2)
// CHECK:STDOUT: !23 = !DILocation(line: 29, column: 15, scope: !22)
// CHECK:STDOUT: !24 = !DILocation(line: 29, column: 1, scope: !22)