Index: llvm/lib/Transforms/InstCombine/InstructionCombining.cpp =================================================================== --- llvm/lib/Transforms/InstCombine/InstructionCombining.cpp +++ llvm/lib/Transforms/InstCombine/InstructionCombining.cpp @@ -3211,6 +3211,17 @@ // Check to see if we can DCE the instruction. if (isInstructionTriviallyDead(I, &TLI)) { LLVM_DEBUG(dbgs() << "IC: DCE: " << *I << '\n'); + + SmallVector DbgUsers; + findDbgUsers(DbgUsers, I); + if (!DbgUsers.empty()) { + for (auto *DII : DbgUsers) { + Value *Undef = UndefValue::get(I->getType()); + DII->setOperand(0, MetadataAsValue::get(DII->getContext(), + ValueAsMetadata::get(Undef))); + } + } + eraseInstFromFunction(*I); ++NumDeadInst; MadeIRChange = true; Index: llvm/test/Transforms/InstCombine/pr43893.ll =================================================================== --- /dev/null +++ llvm/test/Transforms/InstCombine/pr43893.ll @@ -0,0 +1,61 @@ +; RUN: opt -instcombine -S -o - %s | FileCheck %s + +@a = common dso_local global i8 0, align 1, !dbg !0 +@b = common dso_local global i8 0, align 1, !dbg !6 + +; Function Attrs: noinline nounwind uwtable +define dso_local i32 @main() #0 !dbg !13 { +entry: + %0 = load i8, i8* @a, align 1, !dbg !17 + %dec = add i8 %0, -1, !dbg !17 + store i8 %dec, i8* @a, align 1, !dbg !17 +;CHECK: call void @llvm.dbg.value(metadata i32 undef +;CHECK: call void @llvm.dbg.value(metadata i32 -8 +;CHECK call void @llvm.dbg.value(metadata i32 undef + %conv = sext i8 %dec to i32, !dbg !17 + call void @llvm.dbg.value(metadata i32 %conv, metadata !18, metadata !DIExpression()), !dbg !19 + call void @llvm.dbg.value(metadata i32 -8, metadata !20, metadata !DIExpression()), !dbg !19 + call void @llvm.dbg.value(metadata i32 %conv, metadata !20, metadata !DIExpression()), !dbg !19 + store i8 0, i8* @b, align 1, !dbg !21 + %cmp = icmp sgt i32 %conv, 0, !dbg !22 + %conv1 = zext i1 %cmp to i32, !dbg !22 + ret i32 0, !dbg !23 +} + +; Function Attrs: nounwind readnone speculatable willreturn +declare void @llvm.dbg.declare(metadata, metadata, metadata) #1 + +; Function Attrs: nounwind readnone speculatable willreturn +declare void @llvm.dbg.value(metadata, metadata, metadata) #1 + +attributes #0 = { noinline nounwind uwtable } +attributes #1 = { nounwind readnone speculatable willreturn } + +!llvm.dbg.cu = !{!2} +!llvm.module.flags = !{!9, !10, !11} +!llvm.ident = !{!12} + +!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression()) +!1 = distinct !DIGlobalVariable(name: "a", scope: !2, file: !3, line: 1, type: !8, isLocal: false, isDefinition: true) +!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 10.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5, nameTableKind: None) +!3 = !DIFile(filename: "test", directory: "n") +!4 = !{} +!5 = !{!0, !6} +!6 = !DIGlobalVariableExpression(var: !7, expr: !DIExpression()) +!7 = distinct !DIGlobalVariable(name: "b", scope: !2, file: !3, line: 1, type: !8, isLocal: false, isDefinition: true) +!8 = !DIBasicType(name: "char", size: 8, encoding: DW_ATE_signed_char) +!9 = !{i32 2, !"Dwarf Version", i32 4} +!10 = !{i32 2, !"Debug Info Version", i32 3} +!11 = !{i32 1, !"wchar_size", i32 4} +!12 = !{!"clang version 10.0.0"} +!13 = distinct !DISubprogram(name: "main", scope: !3, file: !3, line: 2, type: !14, scopeLine: 2, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !4) +!14 = !DISubroutineType(types: !15) +!15 = !{!16} +!16 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed) +!17 = !DILocation(line: 4, column: 11, scope: !13) +!18 = !DILocalVariable(name: "c", scope: !13, file: !3, line: 4, type: !16) +!19 = !DILocation(line: 0, scope: !13) +!20 = !DILocalVariable(name: "l_1240", scope: !13, file: !3, line: 6, type: !16) +!21 = !DILocation(line: 10, column: 10, scope: !13) +!22 = !DILocation(line: 10, column: 5, scope: !13) +!23 = !DILocation(line: 12, column: 1, scope: !13)