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[DebugInfo] Corrections for salvageDebugInfo 

Summary:
When salvaging a dbg.declare/dbg.addr we should not add
DW_OP_stack_value to the DIExpression
(see test/Transforms/InstCombine/salvage-dbg-declare.ll).

Consider this example
  %vla = alloca i32, i64 2
  call void @llvm.dbg.declare(metadata i32* %vla, metadata !1, metadata !DIExpression())

Instcombine will turn it into
  %vla1 = alloca [2 x i32]
  %vla1.sub = getelementptr inbounds [2 x i32], [2 x i32]* %vla, i64 0, i64 0
  call void @llvm.dbg.declare(metadata [2 x i32]* %vla1.sub, metadata !19, metadata !DIExpression())

If the GEP can be eliminated, then the dbg.declare will be salvaged
and we should get
  %vla1 = alloca [2 x i32]
  call void @llvm.dbg.declare(metadata [2 x i32]* %vla1, metadata !19, metadata !DIExpression())

The problem was that salvageDebugInfo did not recognize dbg.declare
as being indirect (%vla1 points to the value, it does not hold the
value), so we incorrectly got
  call void @llvm.dbg.declare(metadata [2 x i32]* %vla1, metadata !19, metadata !DIExpression(DW_OP_stack_value))

I also made sure that llvm::salvageDebugInfo and
DIExpression::prependOpcodes do not add DW_OP_stack_value to
the DIExpression in case no new operands are added to the
DIExpression. That way we avoid to, unneccessarily, turn a
register location expression into an implicit location expression
in some situations (see test11 in test/Transforms/LICM/sinking.ll).

Reviewers: aprantl, vsk

Reviewed By: aprantl, vsk

Subscribers: JDevlieghere, llvm-commits

Differential Revision: https://reviews.llvm.org/D48837

llvm-svn: 336191
This commit is contained in:
Bjorn Pettersson 2018-07-03 11:29:00 +00:00
parent fd171f2f89
commit 8dd6cf711f
4 changed files with 68 additions and 4 deletions
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3
llvm/lib/IR/DebugInfoMetadata.cpp
View File

@ -803,6 +803,9 @@ DIExpression *DIExpression::prepend(const DIExpression *Expr, bool DerefBefore,
DIExpression *DIExpression::prependOpcodes(const DIExpression *Expr,
SmallVectorImpl<uint64_t> &Ops,
bool StackValue) {
// If there are no ops to prepend, do not even add the DW_OP_stack_value.
if (Ops.empty())
StackValue = false;
if (Expr)
for (auto Op : Expr->expr_ops()) {
// A DW_OP_stack_value comes at the end, but before a DW_OP_LLVM_fragment.

9
llvm/lib/Transforms/Utils/Local.cpp
View File

@ -1605,8 +1605,13 @@ void llvm::salvageDebugInfo(Instruction &I) {
auto doSalvage = [&](DbgInfoIntrinsic *DII, SmallVectorImpl<uint64_t> &Ops) {
auto *DIExpr = DII->getExpression();
DIExpr =
DIExpression::prependOpcodes(DIExpr, Ops, DIExpression::WithStackValue);
if (!Ops.empty()) {
// Do not add DW_OP_stack_value for DbgDeclare and DbgAddr, because they
// are implicitly pointing out the value as a DWARF memory location
// description.
bool WithStackValue = isa<DbgValueInst>(DII);
DIExpr = DIExpression::prependOpcodes(DIExpr, Ops, WithStackValue);
}
DII->setOperand(0, wrapMD(I.getOperand(0)));
DII->setOperand(2, MetadataAsValue::get(I.getContext(), DIExpr));
LLVM_DEBUG(dbgs() << "SALVAGE: " << *DII << '\n');

49
llvm/test/Transforms/InstCombine/salvage-dbg-declare.ll Normal file
View File

@ -0,0 +1,49 @@
; RUN: opt -instcombine -S -o - %s | FileCheck %s
declare dso_local i32 @bar(i8*)
; Function Attrs: nounwind
define internal i32 @foo() #0 !dbg !1 {
; CHECK: %[[VLA:.*]] = alloca [2 x i32]
; CHECK: call void @llvm.dbg.declare(metadata [2 x i32]* %[[VLA]], {{.*}}, metadata !DIExpression())
entry:
%vla = alloca i32, i64 2, align 4, !dbg !16
call void @llvm.dbg.declare(metadata i32* %vla, metadata !19, metadata !DIExpression()), !dbg !20
%0 = bitcast i32* %vla to i8*, !dbg !21
%call = call i32 @bar(i8* %0), !dbg !22
unreachable
}
; Function Attrs: nounwind readnone speculatable
declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
attributes #0 = { nounwind }
attributes #1 = { nounwind readnone speculatable }
!llvm.dbg.cu = !{!5}
!llvm.module.flags = !{!0}
!0 = !{i32 2, !"Debug Info Version", i32 3}
!1 = distinct !DISubprogram(name: "a", scope: !2, file: !2, line: 232, type: !3, isLocal: true, isDefinition: true, scopeLine: 234, flags: DIFlagPrototyped, isOptimized: true, unit: !5, retainedNodes: !6)
!2 = !DIFile(filename: "b", directory: "c")
!3 = !DISubroutineType(types: !4)
!4 = !{}
!5 = distinct !DICompileUnit(language: DW_LANG_C99, file: !2, producer: "clang version", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, retainedTypes: !4, globals: !4)
!6 = !{!7, !11}
!7 = !DILocalVariable(name: "__vla_expr", scope: !8, type: !10, flags: DIFlagArtificial)
!8 = distinct !DILexicalBlock(scope: !9, file: !2, line: 238, column: 39)
!9 = distinct !DILexicalBlock(scope: !1, file: !2, line: 238, column: 6)
!10 = !DIBasicType(name: "long unsigned int", size: 64, encoding: DW_ATE_unsigned)
!11 = !DILocalVariable(name: "ptr32", scope: !8, file: !2, line: 240, type: !12)
!12 = !DICompositeType(tag: DW_TAG_array_type, baseType: !13, elements: !14)
!13 = !DIBasicType(name: "unsigned int", size: 32, encoding: DW_ATE_unsigned)
!14 = !{!15}
!15 = !DISubrange(count: !7)
!16 = !DILocation(line: 240, column: 3, scope: !17)
!17 = distinct !DILexicalBlock(scope: !18, file: !2, line: 238, column: 39)
!18 = distinct !DILexicalBlock(scope: !1, file: !2, line: 238, column: 6)
!19 = !DILocalVariable(name: "ptr32", scope: !17, file: !2, line: 240, type: !12)
!20 = !DILocation(line: 240, column: 12, scope: !17)
!21 = !DILocation(line: 241, column: 65, scope: !17)
!22 = !DILocation(line: 241, column: 11, scope: !17)

11
llvm/test/Transforms/LICM/sinking.ll
View File

@ -243,7 +243,8 @@ Out: ; preds = %Loop
define void @test11() {
br label %Loop
Loop:
%dead = getelementptr %Ty, %Ty* @X2, i64 0, i32 0
%dead1 = getelementptr %Ty, %Ty* @X2, i64 0, i32 0
%dead2 = getelementptr %Ty, %Ty* @X2, i64 0, i32 1
br i1 false, label %Loop, label %Out
Out:
ret void
@ -251,8 +252,14 @@ Out:
; CHECK: Out:
; CHECK-NEXT: ret void
; The GEP in dead1 is adding a zero offset, so the DIExpression can be kept as
; a "register location".
; The GEP in dead2 is adding a 4 bytes to the pointer, so the DIExpression is
; turned into an "implicit location" using DW_OP_stack_value.
;
; DEBUGIFY-LABEL: @test11(
; DEBUGIFY: call void @llvm.dbg.value(metadata %Ty* @X2, metadata {{.*}}, metadata !DIExpression(DW_OP_stack_value))
; DEBUGIFY: call void @llvm.dbg.value(metadata %Ty* @X2, metadata {{.*}}, metadata !DIExpression())
; DEBUGIFY: call void @llvm.dbg.value(metadata %Ty* @X2, metadata {{.*}}, metadata !DIExpression(DW_OP_plus_uconst, 4, DW_OP_stack_value))
}
@c = common global [1 x i32] zeroinitializer, align 4