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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/class/basic.carbon
Vendored
+21 -21
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@@ -28,20 +28,20 @@ fn Run() {
// CHECK:STDOUT: declare void @_CF.Main(ptr sret({ i32, ptr }), ptr)
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define void @main() #0 !dbg !4 {
// CHECK:STDOUT: define i32 @main() #0 !dbg !4 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %c.var = alloca { i32, ptr }, align 8, !dbg !7
// CHECK:STDOUT: %_.var = alloca { i32, ptr }, align 8, !dbg !8
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %c.var), !dbg !7
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %_.var), !dbg !8
// CHECK:STDOUT: call void @_CF.Main(ptr %_.var, ptr %c.var), !dbg !9
// CHECK:STDOUT: call void @"_COp.71e25083d63c4d6c:core.Destroy.Core"(ptr %_.var), !dbg !8
// CHECK:STDOUT: call void @"_COp.71e25083d63c4d6c:core.Destroy.Core"(ptr %c.var), !dbg !7
// CHECK:STDOUT: ret void, !dbg !10
// CHECK:STDOUT: %c.var = alloca { i32, ptr }, align 8, !dbg !8
// CHECK:STDOUT: %_.var = alloca { i32, ptr }, align 8, !dbg !9
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %c.var), !dbg !8
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %_.var), !dbg !9
// CHECK:STDOUT: call void @_CF.Main(ptr %_.var, ptr %c.var), !dbg !10
// CHECK:STDOUT: call void @"_COp.71e25083d63c4d6c:core.Destroy.Core"(ptr %_.var), !dbg !9
// CHECK:STDOUT: call void @"_COp.71e25083d63c4d6c:core.Destroy.Core"(ptr %c.var), !dbg !8
// CHECK:STDOUT: ret i32 0, !dbg !11
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define weak_odr void @"_COp.7e389eab4a7e5487:core.Destroy.Core"(ptr %self) #0 !dbg !11 {
// CHECK:STDOUT: define weak_odr void @"_COp.7e389eab4a7e5487:core.Destroy.Core"(ptr %self) #0 !dbg !12 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: ret void, !dbg !17
// CHECK:STDOUT: }
@@ -77,18 +77,18 @@ fn Run() {
// CHECK:STDOUT: !3 = !DIFile(filename: "basic.carbon", directory: "")
// CHECK:STDOUT: !4 = distinct !DISubprogram(name: "Run", linkageName: "main", scope: null, file: !3, line: 20, type: !5, spFlags: DISPFlagDefinition, unit: !2)
// CHECK:STDOUT: !5 = !DISubroutineType(types: !6)
// CHECK:STDOUT: !6 = !{null}
// CHECK:STDOUT: !7 = !DILocation(line: 21, column: 3, scope: !4)
// CHECK:STDOUT: !8 = !DILocation(line: 22, column: 3, scope: !4)
// CHECK:STDOUT: !9 = !DILocation(line: 22, column: 14, scope: !4)
// CHECK:STDOUT: !10 = !DILocation(line: 20, column: 1, scope: !4)
// CHECK:STDOUT: !11 = distinct !DISubprogram(name: "Op", linkageName: "_COp.7e389eab4a7e5487:core.Destroy.Core", scope: null, file: !3, line: 22, type: !12, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !15)
// CHECK:STDOUT: !12 = !DISubroutineType(types: !13)
// CHECK:STDOUT: !13 = !{null, !14}
// CHECK:STDOUT: !14 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
// CHECK:STDOUT: !6 = !{!7}
// CHECK:STDOUT: !7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
// CHECK:STDOUT: !8 = !DILocation(line: 21, column: 3, scope: !4)
// CHECK:STDOUT: !9 = !DILocation(line: 22, column: 3, scope: !4)
// CHECK:STDOUT: !10 = !DILocation(line: 22, column: 14, scope: !4)
// CHECK:STDOUT: !11 = !DILocation(line: 20, column: 1, scope: !4)
// CHECK:STDOUT: !12 = distinct !DISubprogram(name: "Op", linkageName: "_COp.7e389eab4a7e5487:core.Destroy.Core", scope: null, file: !3, line: 22, type: !13, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !15)
// CHECK:STDOUT: !13 = !DISubroutineType(types: !14)
// CHECK:STDOUT: !14 = !{null, !7}
// CHECK:STDOUT: !15 = !{!16}
// CHECK:STDOUT: !16 = !DILocalVariable(arg: 1, scope: !11, type: !14)
// CHECK:STDOUT: !17 = !DILocation(line: 22, column: 3, scope: !11)
// CHECK:STDOUT: !16 = !DILocalVariable(arg: 1, scope: !12, type: !7)
// CHECK:STDOUT: !17 = !DILocation(line: 22, column: 3, scope: !12)
// CHECK:STDOUT: !18 = distinct !DISubprogram(name: "Op", linkageName: "_COp.e7e7253cfbad8551:core.Destroy.Core", scope: null, file: !3, line: 22, type: !19, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !22)
// CHECK:STDOUT: !19 = !DISubroutineType(types: !20)
// CHECK:STDOUT: !20 = !{null, !21}