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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/index/array_element_access.carbon
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+55 -55
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@@ -45,49 +45,49 @@ fn Run() {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define void @main() #0 !dbg !13 {
// CHECK:STDOUT: define i32 @main() #0 !dbg !13 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %a.var = alloca [2 x i32], align 4, !dbg !16
// CHECK:STDOUT: %.loc17_28.1.temp = alloca { i32, i32 }, align 8, !dbg !17
// CHECK:STDOUT: %b.var = alloca i32, align 4, !dbg !18
// CHECK:STDOUT: %_.var.loc19 = alloca i32, align 4, !dbg !19
// CHECK:STDOUT: %_.var.loc20 = alloca i32, align 4, !dbg !20
// CHECK:STDOUT: %.loc20_18.1.temp = alloca [2 x i32], align 4, !dbg !21
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %a.var), !dbg !16
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.loc17_28.1.temp), !dbg !17
// CHECK:STDOUT: call void @_CA.Main(ptr %.loc17_28.1.temp), !dbg !17
// CHECK:STDOUT: %tuple.elem0.tuple.elem = getelementptr inbounds nuw { i32, i32 }, ptr %.loc17_28.1.temp, i32 0, i32 0, !dbg !17
// CHECK:STDOUT: %.loc17_28.3 = load i32, ptr %tuple.elem0.tuple.elem, align 4, !dbg !17
// CHECK:STDOUT: %.loc17_28.4.array.index = getelementptr inbounds [2 x i32], ptr %a.var, i32 0, i64 0, !dbg !17
// CHECK:STDOUT: store i32 %.loc17_28.3, ptr %.loc17_28.4.array.index, align 4, !dbg !17
// CHECK:STDOUT: %tuple.elem1.tuple.elem = getelementptr inbounds nuw { i32, i32 }, ptr %.loc17_28.1.temp, i32 0, i32 1, !dbg !17
// CHECK:STDOUT: %.loc17_28.6 = load i32, ptr %tuple.elem1.tuple.elem, align 4, !dbg !17
// CHECK:STDOUT: %.loc17_28.7.array.index = getelementptr inbounds [2 x i32], ptr %a.var, i32 0, i64 1, !dbg !17
// CHECK:STDOUT: store i32 %.loc17_28.6, ptr %.loc17_28.7.array.index, align 4, !dbg !17
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %b.var), !dbg !18
// CHECK:STDOUT: store i32 1, ptr %b.var, align 4, !dbg !18
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %_.var.loc19), !dbg !19
// CHECK:STDOUT: %.loc19_18 = load i32, ptr %b.var, align 4, !dbg !22
// CHECK:STDOUT: %.loc19_19.1.array.index = getelementptr inbounds [2 x i32], ptr %a.var, i32 0, i32 %.loc19_18, !dbg !23
// CHECK:STDOUT: %.loc19_19.2 = load i32, ptr %.loc19_19.1.array.index, align 4, !dbg !23
// CHECK:STDOUT: store i32 %.loc19_19.2, ptr %_.var.loc19, align 4, !dbg !19
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %_.var.loc20), !dbg !20
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.loc20_18.1.temp), !dbg !21
// CHECK:STDOUT: call void @_CB.Main(ptr %.loc20_18.1.temp), !dbg !21
// CHECK:STDOUT: %.loc20_21.1.array.index = getelementptr inbounds [2 x i32], ptr %.loc20_18.1.temp, i32 0, i32 1, !dbg !21
// CHECK:STDOUT: %.loc20_21.2 = load i32, ptr %.loc20_21.1.array.index, align 4, !dbg !21
// CHECK:STDOUT: store i32 %.loc20_21.2, ptr %_.var.loc20, align 4, !dbg !20
// CHECK:STDOUT: call void @"_COp.f53f00a5f9e218d2:core.Destroy.Core"(ptr %.loc20_18.1.temp), !dbg !21
// CHECK:STDOUT: call void @"_COp.7e389eab4a7e5487:core.Destroy.Core"(ptr %_.var.loc20), !dbg !20
// CHECK:STDOUT: call void @"_COp.7e389eab4a7e5487:core.Destroy.Core"(ptr %_.var.loc19), !dbg !19
// CHECK:STDOUT: call void @"_COp.7e389eab4a7e5487:core.Destroy.Core"(ptr %b.var), !dbg !18
// CHECK:STDOUT: call void @"_COp.8e354c83fe88ab86:core.Destroy.Core"(ptr %.loc17_28.1.temp), !dbg !17
// CHECK:STDOUT: call void @"_COp.f53f00a5f9e218d2:core.Destroy.Core"(ptr %a.var), !dbg !16
// CHECK:STDOUT: ret void, !dbg !24
// CHECK:STDOUT: %a.var = alloca [2 x i32], align 4, !dbg !17
// CHECK:STDOUT: %.loc17_28.1.temp = alloca { i32, i32 }, align 8, !dbg !18
// CHECK:STDOUT: %b.var = alloca i32, align 4, !dbg !19
// CHECK:STDOUT: %_.var.loc19 = alloca i32, align 4, !dbg !20
// CHECK:STDOUT: %_.var.loc20 = alloca i32, align 4, !dbg !21
// CHECK:STDOUT: %.loc20_18.1.temp = alloca [2 x i32], align 4, !dbg !22
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %a.var), !dbg !17
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.loc17_28.1.temp), !dbg !18
// CHECK:STDOUT: call void @_CA.Main(ptr %.loc17_28.1.temp), !dbg !18
// CHECK:STDOUT: %tuple.elem0.tuple.elem = getelementptr inbounds nuw { i32, i32 }, ptr %.loc17_28.1.temp, i32 0, i32 0, !dbg !18
// CHECK:STDOUT: %.loc17_28.3 = load i32, ptr %tuple.elem0.tuple.elem, align 4, !dbg !18
// CHECK:STDOUT: %.loc17_28.4.array.index = getelementptr inbounds [2 x i32], ptr %a.var, i32 0, i64 0, !dbg !18
// CHECK:STDOUT: store i32 %.loc17_28.3, ptr %.loc17_28.4.array.index, align 4, !dbg !18
// CHECK:STDOUT: %tuple.elem1.tuple.elem = getelementptr inbounds nuw { i32, i32 }, ptr %.loc17_28.1.temp, i32 0, i32 1, !dbg !18
// CHECK:STDOUT: %.loc17_28.6 = load i32, ptr %tuple.elem1.tuple.elem, align 4, !dbg !18
// CHECK:STDOUT: %.loc17_28.7.array.index = getelementptr inbounds [2 x i32], ptr %a.var, i32 0, i64 1, !dbg !18
// CHECK:STDOUT: store i32 %.loc17_28.6, ptr %.loc17_28.7.array.index, align 4, !dbg !18
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %b.var), !dbg !19
// CHECK:STDOUT: store i32 1, ptr %b.var, align 4, !dbg !19
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %_.var.loc19), !dbg !20
// CHECK:STDOUT: %.loc19_18 = load i32, ptr %b.var, align 4, !dbg !23
// CHECK:STDOUT: %.loc19_19.1.array.index = getelementptr inbounds [2 x i32], ptr %a.var, i32 0, i32 %.loc19_18, !dbg !24
// CHECK:STDOUT: %.loc19_19.2 = load i32, ptr %.loc19_19.1.array.index, align 4, !dbg !24
// CHECK:STDOUT: store i32 %.loc19_19.2, ptr %_.var.loc19, align 4, !dbg !20
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %_.var.loc20), !dbg !21
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.loc20_18.1.temp), !dbg !22
// CHECK:STDOUT: call void @_CB.Main(ptr %.loc20_18.1.temp), !dbg !22
// CHECK:STDOUT: %.loc20_21.1.array.index = getelementptr inbounds [2 x i32], ptr %.loc20_18.1.temp, i32 0, i32 1, !dbg !22
// CHECK:STDOUT: %.loc20_21.2 = load i32, ptr %.loc20_21.1.array.index, align 4, !dbg !22
// CHECK:STDOUT: store i32 %.loc20_21.2, ptr %_.var.loc20, align 4, !dbg !21
// CHECK:STDOUT: call void @"_COp.f53f00a5f9e218d2:core.Destroy.Core"(ptr %.loc20_18.1.temp), !dbg !22
// CHECK:STDOUT: call void @"_COp.7e389eab4a7e5487:core.Destroy.Core"(ptr %_.var.loc20), !dbg !21
// CHECK:STDOUT: call void @"_COp.7e389eab4a7e5487:core.Destroy.Core"(ptr %_.var.loc19), !dbg !20
// CHECK:STDOUT: call void @"_COp.7e389eab4a7e5487:core.Destroy.Core"(ptr %b.var), !dbg !19
// CHECK:STDOUT: call void @"_COp.8e354c83fe88ab86:core.Destroy.Core"(ptr %.loc17_28.1.temp), !dbg !18
// CHECK:STDOUT: call void @"_COp.f53f00a5f9e218d2:core.Destroy.Core"(ptr %a.var), !dbg !17
// CHECK:STDOUT: ret i32 0, !dbg !25
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define weak_odr void @"_COp.7e389eab4a7e5487:core.Destroy.Core"(ptr %self) #0 !dbg !25 {
// CHECK:STDOUT: define weak_odr void @"_COp.7e389eab4a7e5487:core.Destroy.Core"(ptr %self) #0 !dbg !26 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: ret void, !dbg !31
// CHECK:STDOUT: }
@@ -138,23 +138,23 @@ fn Run() {
// CHECK:STDOUT: !12 = !DILocation(line: 14, column: 27, scope: !10)
// CHECK:STDOUT: !13 = distinct !DISubprogram(name: "Run", linkageName: "main", scope: null, file: !3, line: 16, type: !14, spFlags: DISPFlagDefinition, unit: !2)
// CHECK:STDOUT: !14 = !DISubroutineType(types: !15)
// CHECK:STDOUT: !15 = !{null}
// CHECK:STDOUT: !16 = !DILocation(line: 17, column: 3, scope: !13)
// CHECK:STDOUT: !17 = !DILocation(line: 17, column: 26, scope: !13)
// CHECK:STDOUT: !18 = !DILocation(line: 18, column: 3, scope: !13)
// CHECK:STDOUT: !19 = !DILocation(line: 19, column: 3, scope: !13)
// CHECK:STDOUT: !20 = !DILocation(line: 20, column: 3, scope: !13)
// CHECK:STDOUT: !21 = !DILocation(line: 20, column: 16, scope: !13)
// CHECK:STDOUT: !22 = !DILocation(line: 19, column: 18, scope: !13)
// CHECK:STDOUT: !23 = !DILocation(line: 19, column: 16, scope: !13)
// CHECK:STDOUT: !24 = !DILocation(line: 16, column: 1, scope: !13)
// CHECK:STDOUT: !25 = distinct !DISubprogram(name: "Op", linkageName: "_COp.7e389eab4a7e5487:core.Destroy.Core", scope: null, file: !3, line: 20, type: !26, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !29)
// CHECK:STDOUT: !26 = !DISubroutineType(types: !27)
// CHECK:STDOUT: !27 = !{null, !28}
// CHECK:STDOUT: !28 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
// CHECK:STDOUT: !15 = !{!16}
// CHECK:STDOUT: !16 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
// CHECK:STDOUT: !17 = !DILocation(line: 17, column: 3, scope: !13)
// CHECK:STDOUT: !18 = !DILocation(line: 17, column: 26, scope: !13)
// CHECK:STDOUT: !19 = !DILocation(line: 18, column: 3, scope: !13)
// CHECK:STDOUT: !20 = !DILocation(line: 19, column: 3, scope: !13)
// CHECK:STDOUT: !21 = !DILocation(line: 20, column: 3, scope: !13)
// CHECK:STDOUT: !22 = !DILocation(line: 20, column: 16, scope: !13)
// CHECK:STDOUT: !23 = !DILocation(line: 19, column: 18, scope: !13)
// CHECK:STDOUT: !24 = !DILocation(line: 19, column: 16, scope: !13)
// CHECK:STDOUT: !25 = !DILocation(line: 16, column: 1, scope: !13)
// CHECK:STDOUT: !26 = distinct !DISubprogram(name: "Op", linkageName: "_COp.7e389eab4a7e5487:core.Destroy.Core", scope: null, file: !3, line: 20, type: !27, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !29)
// CHECK:STDOUT: !27 = !DISubroutineType(types: !28)
// CHECK:STDOUT: !28 = !{null, !16}
// CHECK:STDOUT: !29 = !{!30}
// CHECK:STDOUT: !30 = !DILocalVariable(arg: 1, scope: !25, type: !28)
// CHECK:STDOUT: !31 = !DILocation(line: 20, column: 16, scope: !25)
// CHECK:STDOUT: !30 = !DILocalVariable(arg: 1, scope: !26, type: !16)
// CHECK:STDOUT: !31 = !DILocation(line: 20, column: 16, scope: !26)
// CHECK:STDOUT: !32 = distinct !DISubprogram(name: "Op", linkageName: "_COp.f53f00a5f9e218d2:core.Destroy.Core", scope: null, file: !3, line: 20, type: !33, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !35)
// CHECK:STDOUT: !33 = !DISubroutineType(types: !34)
// CHECK:STDOUT: !34 = !{null, !7}