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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/tuple/access/return_value_access.carbon
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+23 -23
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@@ -31,23 +31,23 @@ fn Run() {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define void @main() #0 !dbg !10 {
// CHECK:STDOUT: define i32 @main() #0 !dbg !10 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %_.var = alloca i32, align 4, !dbg !13
// CHECK:STDOUT: %.loc16_18.1.temp = alloca { i32, i32 }, align 8, !dbg !14
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %_.var), !dbg !13
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.loc16_18.1.temp), !dbg !14
// CHECK:STDOUT: call void @_CF.Main(ptr %.loc16_18.1.temp), !dbg !14
// CHECK:STDOUT: %tuple.elem1.tuple.elem = getelementptr inbounds nuw { i32, i32 }, ptr %.loc16_18.1.temp, i32 0, i32 1, !dbg !14
// CHECK:STDOUT: %.loc16_19 = load i32, ptr %tuple.elem1.tuple.elem, align 4, !dbg !14
// CHECK:STDOUT: store i32 %.loc16_19, ptr %_.var, align 4, !dbg !13
// CHECK:STDOUT: call void @"_COp.8e354c83fe88ab86:core.Destroy.Core"(ptr %.loc16_18.1.temp), !dbg !14
// CHECK:STDOUT: call void @"_COp.7e389eab4a7e5487:core.Destroy.Core"(ptr %_.var), !dbg !13
// CHECK:STDOUT: ret void, !dbg !15
// CHECK:STDOUT: %_.var = alloca i32, align 4, !dbg !14
// CHECK:STDOUT: %.loc16_18.1.temp = alloca { i32, i32 }, align 8, !dbg !15
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %_.var), !dbg !14
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.loc16_18.1.temp), !dbg !15
// CHECK:STDOUT: call void @_CF.Main(ptr %.loc16_18.1.temp), !dbg !15
// CHECK:STDOUT: %tuple.elem1.tuple.elem = getelementptr inbounds nuw { i32, i32 }, ptr %.loc16_18.1.temp, i32 0, i32 1, !dbg !15
// CHECK:STDOUT: %.loc16_19 = load i32, ptr %tuple.elem1.tuple.elem, align 4, !dbg !15
// CHECK:STDOUT: store i32 %.loc16_19, ptr %_.var, align 4, !dbg !14
// CHECK:STDOUT: call void @"_COp.8e354c83fe88ab86:core.Destroy.Core"(ptr %.loc16_18.1.temp), !dbg !15
// CHECK:STDOUT: call void @"_COp.7e389eab4a7e5487:core.Destroy.Core"(ptr %_.var), !dbg !14
// CHECK:STDOUT: ret i32 0, !dbg !16
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define weak_odr void @"_COp.7e389eab4a7e5487:core.Destroy.Core"(ptr %self) #0 !dbg !16 {
// CHECK:STDOUT: define weak_odr void @"_COp.7e389eab4a7e5487:core.Destroy.Core"(ptr %self) #0 !dbg !17 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: ret void, !dbg !22
// CHECK:STDOUT: }
@@ -86,17 +86,17 @@ fn Run() {
// CHECK:STDOUT: !9 = !DILocation(line: 13, column: 24, scope: !4)
// CHECK:STDOUT: !10 = distinct !DISubprogram(name: "Run", linkageName: "main", scope: null, file: !3, line: 15, type: !11, spFlags: DISPFlagDefinition, unit: !2)
// CHECK:STDOUT: !11 = !DISubroutineType(types: !12)
// CHECK:STDOUT: !12 = !{null}
// CHECK:STDOUT: !13 = !DILocation(line: 16, column: 3, scope: !10)
// CHECK:STDOUT: !14 = !DILocation(line: 16, column: 16, scope: !10)
// CHECK:STDOUT: !15 = !DILocation(line: 15, column: 1, scope: !10)
// CHECK:STDOUT: !16 = distinct !DISubprogram(name: "Op", linkageName: "_COp.7e389eab4a7e5487:core.Destroy.Core", scope: null, file: !3, line: 16, type: !17, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !20)
// CHECK:STDOUT: !17 = !DISubroutineType(types: !18)
// CHECK:STDOUT: !18 = !{null, !19}
// CHECK:STDOUT: !19 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
// CHECK:STDOUT: !12 = !{!13}
// CHECK:STDOUT: !13 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
// CHECK:STDOUT: !14 = !DILocation(line: 16, column: 3, scope: !10)
// CHECK:STDOUT: !15 = !DILocation(line: 16, column: 16, scope: !10)
// CHECK:STDOUT: !16 = !DILocation(line: 15, column: 1, scope: !10)
// CHECK:STDOUT: !17 = distinct !DISubprogram(name: "Op", linkageName: "_COp.7e389eab4a7e5487:core.Destroy.Core", scope: null, file: !3, line: 16, type: !18, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !20)
// CHECK:STDOUT: !18 = !DISubroutineType(types: !19)
// CHECK:STDOUT: !19 = !{null, !13}
// CHECK:STDOUT: !20 = !{!21}
// CHECK:STDOUT: !21 = !DILocalVariable(arg: 1, scope: !16, type: !19)
// CHECK:STDOUT: !22 = !DILocation(line: 16, column: 16, scope: !16)
// CHECK:STDOUT: !21 = !DILocalVariable(arg: 1, scope: !17, type: !13)
// CHECK:STDOUT: !22 = !DILocation(line: 16, column: 16, scope: !17)
// CHECK:STDOUT: !23 = distinct !DISubprogram(name: "Op", linkageName: "_COp.8e354c83fe88ab86:core.Destroy.Core", scope: null, file: !3, line: 16, type: !24, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !26)
// CHECK:STDOUT: !24 = !DISubroutineType(types: !25)
// CHECK:STDOUT: !25 = !{null, !7}