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Globalopt pass produces invalid debug info #100654

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Merged
merged 4 commits into from
Aug 8, 2024
Merged

Globalopt pass produces invalid debug info #100654

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7e2ae7c
Handle dbg.value in SalvageDebugInfo()
ykhatav Jul 25, 2024
31556e7
Apply clang-format
ykhatav Jul 25, 2024
605fbd9
Update test
ykhatav Jul 26, 2024
233ba30
Minor test changes
ykhatav Aug 6, 2024
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6 changes: 6 additions & 0 deletions llvm/lib/IR/Metadata.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -346,6 +346,12 @@ void ReplaceableMetadataImpl::SalvageDebugInfo(const Constant &C) {
MetadataTracking::OwnerTy Owner = Pair.second.first;
if (!Owner)
continue;
// Check for MetadataAsValue.
if (isa<MetadataAsValue *>(Owner)) {
cast<MetadataAsValue *>(Owner)->handleChangedMetadata(
ValueAsMetadata::get(UndefValue::get(C.getType())));
continue;
}
if (!isa<Metadata *>(Owner))
continue;
auto *OwnerMD = dyn_cast_if_present<MDNode>(cast<Metadata *>(Owner));
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1 change: 1 addition & 0 deletions llvm/lib/Transforms/IPO/GlobalOpt.cpp
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Expand Up @@ -1338,6 +1338,7 @@ deleteIfDead(GlobalValue &GV,
if (DeleteFnCallback)
DeleteFnCallback(*F);
}
ReplaceableMetadataImpl::SalvageDebugInfo(GV);
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Is this line necessary? I believe GV.removeDeadConstantUsers(); should already call this if GV is dead, as part of constantIsDead(..., /*RemoveDeadUsers=*/true).

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The loop responsible for removing dead users and potentially calling constantIsDead() does not execute in this case. It looks like both the iterators I and E are null indicating it does not count debug intrinsic as users.

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It might be more appropriate to put this into removeDeadConstantUsers then, after the loop - I think we'd want to perform the salvage step for any constant that dies with debug users regardless of the pass that does it. However, that might end up affecting other tests; if so it can easily be left for another patch.

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Yes, I can investigate more and follow up on a different patch if it's a viable approach.

GV.eraseFromParent();
++NumDeleted;
return true;
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34 changes: 34 additions & 0 deletions llvm/test/DebugInfo/X86/undef-dbg-val.ll
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@@ -0,0 +1,34 @@
; RUN: opt -S -passes=globalopt --experimental-debuginfo-iterators=false <%s | FileCheck %s
; CHECK: #dbg_value(ptr undef,
; CHECK-SAME: [[VAR:![0-9]+]],
; CHECK-SAME: !DIExpression()
; CHECK: [[VAR]] = !DILocalVariable(name: "_format"


; ModuleID = '<stdin>'
source_filename = "test.cpp"

@_ZZZZ4main_format = internal constant [24 x i8] c"Result1: Hello, World!\0A\00", align 16, !dbg !9

define void @foo() align 2 !dbg !5 {
entry:
call void @llvm.dbg.value(metadata ptr @_ZZZZ4main_format, metadata !11, metadata !DIExpression()), !dbg !12
ret void
}

!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!3, !4}

!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang", isOptimized: true, emissionKind: FullDebug)
!1 = !DIFile(filename: "test.cpp", directory: "/path/to")
!2 = !{}
!3 = !{i32 7, !"Dwarf Version", i32 4}
!4 = !{i32 2, !"Debug Info Version", i32 3}
!5 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 27, type: !6, scopeLine: 27, spFlags: DISPFlagDefinition, unit: !0)
!6 = !DISubroutineType(types: !7)
!7 = !{null}
!8 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
!9 = !DIGlobalVariableExpression(var: !10, expr: !DIExpression())
!10 = distinct !DIGlobalVariable(name: "_format", scope: !5, file: !1, line: 49, type: !8, isLocal: true, isDefinition: true)
!11 = !DILocalVariable(name: "_format", arg: 1, scope: !5, file: !1, line: 79, type: !8)
!12 = !DILocation(line: 0, scope: !5)
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