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[InstCombine][DebugInfo] Fold constants wrapped in metadata 

Summary:
When constant folding, constants that are wrapped in metadata were not
folded. This could lead to dbg.values being the only user of a constant
expression, due to the non-dbg uses having been rewritten, resulting in
the constant later on being removed by some other pass. This occurred
with the attached test case, in which the non-rewritten GEP in the
dbg.value intrinsic was later on removed by globalopt.

This patch makes the code look through metadata and fold such constants.

I guess that we in the future may want to allow dbg.values using GEPs and
other constant expressions to be emittable even if there are no non-dbg
uses, but for example SelectionDAG does not support that.

Reviewers: jmorse, aprantl, vsk, davide

Reviewed By: aprantl, vsk, davide

Subscribers: hiraditya, llvm-commits

Tags: #debug-info, #llvm

Differential Revision: https://reviews.llvm.org/D73630
This commit is contained in:
David Stenberg 2020-01-30 15:33:28 +01:00
parent d6b83d6ba5
commit b54a8ec1bc
2 changed files with 76 additions and 3 deletions
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20
llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
View File

@ -3561,10 +3561,20 @@ static bool AddReachableCodeToWorklist(BasicBlock *BB, const DataLayout &DL,
// See if we can constant fold its operands.
for (Use &U : Inst->operands()) {
if (!isa<ConstantVector>(U) && !isa<ConstantExpr>(U))
bool WrapAsMetadata = false;
auto *V = cast<Value>(U);
// Look through metadata wrappers.
if (auto *MAV = dyn_cast<MetadataAsValue>(V))
if (auto *VAM = dyn_cast<ValueAsMetadata>(MAV->getMetadata())) {
V = VAM->getValue();
WrapAsMetadata = true;
}
if (!isa<ConstantVector>(V) && !isa<ConstantExpr>(V))
continue;
auto *C = cast<Constant>(U);
auto *C = cast<Constant>(V);
Constant *&FoldRes = FoldedConstants[C];
if (!FoldRes)
FoldRes = ConstantFoldConstant(C, DL, TLI);
@ -3575,7 +3585,11 @@ static bool AddReachableCodeToWorklist(BasicBlock *BB, const DataLayout &DL,
LLVM_DEBUG(dbgs() << "IC: ConstFold operand of: " << *Inst
<< "\n Old = " << *C
<< "\n New = " << *FoldRes << '\n');
U = FoldRes;
if (WrapAsMetadata)
U = MetadataAsValue::get(Inst->getContext(),
ValueAsMetadata::get(FoldRes));
else
U = FoldRes;
MadeIRChange = true;
}
}

59
llvm/test/Transforms/InstCombine/constant-fold-metadata-wrapped.ll Normal file
View File

@ -0,0 +1,59 @@
; RUN: opt -S -instcombine %s -o - | FileCheck %s
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
%struct.Foo = type { i32 }
@global = common global %struct.Foo zeroinitializer, align 4
; Verify that we constant fold the GEP in the llvm.dbg.value intrinsic. We
; want it to match with the non-dbg GEP, so that the debug information can be
; emitted later on.
; When constant folding the GEP the index operand types are canonicalized, so
; we get an i64 operand here.
; CHECK: call void @llvm.dbg.value(metadata i32* getelementptr inbounds (%struct.Foo, %struct.Foo* @global, i64 0, i32 0)
; CHECK: call void @ext(i32* getelementptr inbounds (%struct.Foo, %struct.Foo* @global, i64 0, i32 0))
; Function Attrs: nounwind uwtable
define i32 @main() #0 !dbg !13 {
entry:
call void @llvm.dbg.value(metadata i32* getelementptr inbounds (%struct.Foo, %struct.Foo* @global, i32 0, i32 0), metadata !17, metadata !DIExpression()), !dbg !18
call void @ext(i32* getelementptr inbounds (%struct.Foo, %struct.Foo* @global, i32 0, i32 0)), !dbg !19
ret i32 0, !dbg !20
}
declare !dbg !4 void @ext(i32*)
; Function Attrs: nounwind readnone speculatable willreturn
declare void @llvm.dbg.value(metadata, metadata, metadata) #1
attributes #0 = { nounwind uwtable }
attributes #1 = { nounwind readnone speculatable willreturn }
!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!9, !10, !11}
!llvm.ident = !{!12}
!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 11.0.0 ", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !3, globals: !2, splitDebugInlining: false, nameTableKind: None)
!1 = !DIFile(filename: "foo.c", directory: "/")
!2 = !{}
!3 = !{!4}
!4 = !DISubprogram(name: "ext", scope: !1, file: !1, line: 3, type: !5, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !2)
!5 = !DISubroutineType(types: !6)
!6 = !{null, !7}
!7 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !8, size: 64)
!8 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
!9 = !{i32 7, !"Dwarf Version", i32 4}
!10 = !{i32 2, !"Debug Info Version", i32 3}
!11 = !{i32 1, !"wchar_size", i32 4}
!12 = !{!"clang version 11.0.0 "}
!13 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 5, type: !14, scopeLine: 5, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !16)
!14 = !DISubroutineType(types: !15)
!15 = !{!8}
!16 = !{!17}
!17 = !DILocalVariable(name: "local", scope: !13, file: !1, line: 6, type: !7)
!18 = !DILocation(line: 0, scope: !13)
!19 = !DILocation(line: 7, scope: !13)
!20 = !DILocation(line: 8, scope: !13)