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[instcombine] Sunk instructions with invalid source location.
When the 'int Four = Two;' is sunk into the 'case 0:' block, the debug value for 'Three' is set incorrectly to 'poison'. Reviewed By: aprantl Differential Revision: https://reviews.llvm.org/D158171
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2 files changed

+103
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‎llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

Lines changed: 12 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -3857,10 +3857,18 @@ bool InstCombinerImpl::tryToSinkInstruction(Instruction *I,
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// here, but that computation has been sunk.
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SmallVector<DbgVariableIntrinsic *, 2> DbgUsers;
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findDbgUsers(DbgUsers, I);
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// Process the sinking DbgUsers in reverse order, as we only want to clone the
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// last appearing debug intrinsic for each given variable.
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// For all debug values in the destination block, the sunk instruction
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// will still be available, so they do not need to be dropped.
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SmallVector<DbgVariableIntrinsic *, 2> DbgUsersToSalvage;
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for (auto &DbgUser : DbgUsers)
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if (DbgUser->getParent() != DestBlock)
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DbgUsersToSalvage.push_back(DbgUser);
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// Process the sinking DbgUsersToSalvage in reverse order, as we only want
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// to clone the last appearing debug intrinsic for each given variable.
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SmallVector<DbgVariableIntrinsic *, 2> DbgUsersToSink;
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for (DbgVariableIntrinsic *DVI : DbgUsers)
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for (DbgVariableIntrinsic *DVI : DbgUsersToSalvage)
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if (DVI->getParent() == SrcBlock)
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DbgUsersToSink.push_back(DVI);
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llvm::sort(DbgUsersToSink,
@@ -3896,7 +3904,7 @@ bool InstCombinerImpl::tryToSinkInstruction(Instruction *I,
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// Perform salvaging without the clones, then sink the clones.
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if (!DIIClones.empty()) {
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salvageDebugInfoForDbgValues(*I, DbgUsers);
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salvageDebugInfoForDbgValues(*I, DbgUsersToSalvage);
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// The clones are in reverse order of original appearance, reverse again to
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// maintain the original order.
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for (auto &DIIClone : llvm::reverse(DIIClones)) {

‎llvm/test/Transforms/InstCombine/sink-instruction-introduces-unnecessary-poison-value.ll

Lines changed: 91 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,91 @@
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; RUN: opt -passes=instcombine -S -o - < %s | FileCheck %s
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; When the 'int Four = Two;' is sunk into the 'case 0:' block,
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; the debug value for 'Three' is set incorrectly to 'poison'.
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; 1 int One = 0;
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; 2 int Two = 0;
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; 3 int test() {
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; 4 int Three = 0;
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; 5 int Four = Two;
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; 6 switch (One) {
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; 7 case 0:
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; 8 Three = Four;
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; 9 break;
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; 10 case 2:
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; 11 Three = 4;
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; 12 break;
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; 13 }
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; 14 return Three;
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; 15 }
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; CHECK-LABEL: sw.bb:
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; CHECK: %[[REG:[0-9]+]] = load i32, ptr @"?Two{{.*}}
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; CHECK: call void @llvm.dbg.value(metadata i32 %[[REG]], metadata ![[DBG1:[0-9]+]], {{.*}}
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; CHECK: call void @llvm.dbg.value(metadata i32 %[[REG]], metadata ![[DBG2:[0-9]+]], {{.*}}
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; CHECK-DAG: ![[DBG1]] = !DILocalVariable(name: "Four"{{.*}})
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; CHECK-DAG: ![[DBG2]] = !DILocalVariable(name: "Three"{{.*}})
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@"?One@@3HA" = dso_local global i32 0, align 4, !dbg !0
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@"?Two@@3HA" = dso_local global i32 0, align 4, !dbg !5
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define dso_local noundef i32 @"?test@@YAHXZ"() !dbg !15 {
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entry:
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call void @llvm.dbg.value(metadata i32 0, metadata !19, metadata !DIExpression()), !dbg !20
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%0 = load i32, ptr @"?Two@@3HA", align 4, !dbg !21
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call void @llvm.dbg.value(metadata i32 %0, metadata !22, metadata !DIExpression()), !dbg !20
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%1 = load i32, ptr @"?One@@3HA", align 4, !dbg !23
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switch i32 %1, label %sw.epilog [
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i32 0, label %sw.bb
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i32 2, label %sw.bb1
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], !dbg !23
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sw.bb: ; preds = %entry
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call void @llvm.dbg.value(metadata i32 %0, metadata !19, metadata !DIExpression()), !dbg !20
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br label %sw.epilog, !dbg !24
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sw.bb1: ; preds = %entry
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call void @llvm.dbg.value(metadata i32 4, metadata !19, metadata !DIExpression()), !dbg !20
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br label %sw.epilog, !dbg !26
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sw.epilog: ; preds = %sw.bb1, %sw.bb, %entry
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%Three.0 = phi i32 [ 0, %entry ], [ 4, %sw.bb1 ], [ %0, %sw.bb ], !dbg !20
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call void @llvm.dbg.value(metadata i32 %Three.0, metadata !19, metadata !DIExpression()), !dbg !20
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ret i32 %Three.0, !dbg !27
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}
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declare void @llvm.dbg.declare(metadata, metadata, metadata)
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declare void @llvm.dbg.value(metadata, metadata, metadata)
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!llvm.dbg.cu = !{!2}
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!llvm.module.flags = !{!8, !9, !10, !11, !12, !13}
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!llvm.ident = !{!14}
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!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
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!1 = distinct !DIGlobalVariable(name: "One", linkageName: "?One@@3HA", scope: !2, file: !3, line: 1, type: !7, isLocal: false, isDefinition: true)
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!2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !3, producer: "clang version 18.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, globals: !4, splitDebugInlining: false, nameTableKind: None)
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!3 = !DIFile(filename: "test.cpp", directory: "")
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!4 = !{!0, !5}
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!5 = !DIGlobalVariableExpression(var: !6, expr: !DIExpression())
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!6 = distinct !DIGlobalVariable(name: "Two", linkageName: "?Two@@3HA", scope: !2, file: !3, line: 2, type: !7, isLocal: false, isDefinition: true)
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!7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
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!8 = !{i32 2, !"CodeView", i32 1}
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!9 = !{i32 2, !"Debug Info Version", i32 3}
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!10 = !{i32 1, !"wchar_size", i32 2}
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!11 = !{i32 8, !"PIC Level", i32 2}
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!12 = !{i32 7, !"uwtable", i32 2}
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!13 = !{i32 1, !"MaxTLSAlign", i32 65536}
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!14 = !{!"clang version 18.0.0"}
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!15 = distinct !DISubprogram(name: "test", linkageName: "?test@@YAHXZ", scope: !3, file: !3, line: 3, type: !16, scopeLine: 3, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !18)
80+
!16 = !DISubroutineType(types: !17)
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!17 = !{!7}
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!18 = !{}
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!19 = !DILocalVariable(name: "Three", scope: !15, file: !3, line: 4, type: !7)
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!20 = !DILocation(line: 0, scope: !15)
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!21 = !DILocation(line: 5, scope: !15)
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!22 = !DILocalVariable(name: "Four", scope: !15, file: !3, line: 5, type: !7)
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!23 = !DILocation(line: 6, scope: !15)
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!24 = !DILocation(line: 9, scope: !25)
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!25 = distinct !DILexicalBlock(scope: !15, file: !3, line: 6)
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!26 = !DILocation(line: 12, scope: !25)
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!27 = !DILocation(line: 14, scope: !15)

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