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Wrong debug info generated at -O2 (-O0 is correct) 

Instcombiner pass was erasing trivially dead instruction without updating dependent llvm.dbg.value.
which was not showing programmer current state of variables while debugging.
As a part of this fix I did following,
Iterate throught all the users (llvm.dbg) of a instruction which is trivially dead and set each if them undef, Before deleting the instruction.
Now user will see optimized out, when try to print those variables.
This fixes
https://bugs.llvm.org/show_bug.cgi?id=43893

This is my first fix to llvm.

Patch by kamlesh kumar!

Differential Revision: https://reviews.llvm.org/D69809
This commit is contained in:
Vedant Kumar 2019-11-07 11:19:41 -08:00
parent ff9d732887
commit a087b78bc4
8 changed files with 73 additions and 8 deletions
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4
llvm/include/llvm/Transforms/Utils/Local.h
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@ -354,6 +354,10 @@ AllocaInst *findAllocaForValue(Value *V,
/// Returns true if any debug users were updated.
bool salvageDebugInfo(Instruction &I);
/// Salvage all debug users of the instruction \p I or mark it as undef if it
/// cannot be salvaged.
void salvageDebugInfoOrMarkUndef(Instruction &I);
/// Implementation of salvageDebugInfo, applying only to instructions in
/// \p Insns, rather than all debug users of \p I.
bool salvageDebugInfoForDbgValues(Instruction &I,

2
llvm/lib/Transforms/InstCombine/InstCombineInternal.h
View File

@ -705,7 +705,7 @@ public:
Instruction *eraseInstFromFunction(Instruction &I) {
LLVM_DEBUG(dbgs() << "IC: ERASE " << I << '\n');
assert(I.use_empty() && "Cannot erase instruction that is used!");
salvageDebugInfo(I);
salvageDebugInfoOrMarkUndef(I);
// Make sure that we reprocess all operands now that we reduced their
// use counts.

3
llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
View File

@ -3414,8 +3414,7 @@ static bool AddReachableCodeToWorklist(BasicBlock *BB, const DataLayout &DL,
if (isInstructionTriviallyDead(Inst, TLI)) {
++NumDeadInst;
LLVM_DEBUG(dbgs() << "IC: DCE: " << *Inst << '\n');
if (!salvageDebugInfo(*Inst))
replaceDbgUsesWithUndef(Inst);
salvageDebugInfoOrMarkUndef(*Inst);
Inst->eraseFromParent();
MadeIRChange = true;
continue;

5
llvm/lib/Transforms/Utils/Local.cpp
View File

@ -1611,6 +1611,11 @@ bool llvm::salvageDebugInfo(Instruction &I) {
return salvageDebugInfoForDbgValues(I, DbgUsers);
}
void llvm::salvageDebugInfoOrMarkUndef(Instruction &I) {
if (!salvageDebugInfo(I))
replaceDbgUsesWithUndef(&I);
}
bool llvm::salvageDebugInfoForDbgValues(
Instruction &I, ArrayRef<DbgVariableIntrinsic *> DbgUsers) {
auto &Ctx = I.getContext();

2
llvm/test/Transforms/InstCombine/cast-mul-select.ll
View File

@ -13,6 +13,8 @@ define i32 @mul(i32 %x, i32 %y) {
; we preserve the debug information in the resulting
; instruction.
; DBGINFO-LABEL: @mul(
; DBGINFO-NEXT: call void @llvm.dbg.value(metadata i8 undef
; DBGINFO-NEXT: call void @llvm.dbg.value(metadata i8 undef
; DBGINFO-NEXT: [[C:%.*]] = mul i32 {{.*}}
; DBGINFO-NEXT: [[D:%.*]] = and i32 {{.*}}
; DBGINFO-NEXT: call void @llvm.dbg.value(metadata i32 [[C]]

2
llvm/test/Transforms/InstCombine/debuginfo-dce.ll
View File

@ -34,7 +34,7 @@ entry:
call void @llvm.dbg.value(metadata %struct.entry* %1, metadata !18, metadata !20), !dbg !19
; CHECK: define void @salvage_load
; CHECK-NEXT: entry:
; CHECK-NOT: dbg.value
; CHECK-NEXT: call void @llvm.dbg.value(metadata %struct.entry* undef
store %struct.entry* %1, %struct.entry** %im_not_dead, align 8
ret void, !dbg !21
}

54
llvm/test/Transforms/InstCombine/pr43893.ll Normal file
View File

@ -0,0 +1,54 @@
; Check for setting dbg.value as undef which depends on trivially dead instructions.
; 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
define dso_local i32 @main() !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
}
declare void @llvm.dbg.value(metadata, metadata, metadata)
!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)

9
llvm/test/Transforms/InstCombine/stacksave-debuginfo.ll
View File

@ -8,10 +8,11 @@ declare void @llvm.stackrestore(i8*) #0
define i32* @test1(i32 %P) !dbg !6 {
; CHECK-LABEL: @test1(
; CHECK-NEXT: [[TMP1:%.*]] = zext i32 [[P:%.*]] to i64, !dbg !12
; CHECK-NEXT: [[A:%.*]] = alloca i32, i64 [[TMP1]], align 4, !dbg !12
; CHECK-NEXT: call void @llvm.dbg.value(metadata i32* [[A]], metadata !11, metadata !DIExpression()), !dbg !12
; CHECK-NEXT: ret i32* [[A]], !dbg !13
; CHECK-NEXT: call void @llvm.dbg.value(metadata i8* undef
; CHECK-NEXT: [[TMP1:%.*]] = zext i32 [[P:%.*]] to i64, !dbg !13
; CHECK-NEXT: [[A:%.*]] = alloca i32, i64 [[TMP1]], align 4, !dbg !13
; CHECK-NEXT: call void @llvm.dbg.value(metadata i32* [[A]]
; CHECK-NEXT: ret i32* [[A]], !dbg !14
;
%tmp = call i8* @llvm.stacksave(), !dbg !12
call void @llvm.dbg.value(metadata i8* %tmp, metadata !9, metadata !DIExpression()), !dbg !12