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InstCombine: ignore debug instructions during fence combine 

We should never get different CodeGen based on whether the code is being
compiled in debug mode so we must skip over @llvm.dbg.value (and similar)
calls.

Should fix at least the worst part of PR37690.

llvm-svn: 334090
This commit is contained in:
Tim Northover 2018-06-06 12:46:02 +00:00
parent bc7cbb7895
commit 9b80060d7b
2 changed files with 31 additions and 1 deletions
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6
llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
View File

@ -3704,7 +3704,11 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
// Fence instruction simplification
Instruction *InstCombiner::visitFenceInst(FenceInst &FI) {
// Remove identical consecutive fences.
if (auto *NFI = dyn_cast<FenceInst>(FI.getNextNode()))
Instruction *Next = FI.getNextNode();
while (Next != nullptr && isa<DbgInfoIntrinsic>(Next))
Next = Next->getNextNode();
if (auto *NFI = dyn_cast<FenceInst>(Next))
if (FI.isIdenticalTo(NFI))
return eraseInstFromFunction(FI);
return nullptr;

26
llvm/test/Transforms/InstCombine/consecutive-fences.ll
View File

@ -45,3 +45,29 @@ define void @patatino() {
fence seq_cst
ret void
}
; CHECK-LABEL: define void @debug
; CHECK-NOT: fence
; CHECK: call void @llvm.dbg.value
; CHECK: fence seq_cst
define void @debug() {
fence seq_cst
tail call void @llvm.dbg.value(metadata i32 5, metadata !1, metadata !DIExpression()), !dbg !9
fence seq_cst
ret void
}
declare void @llvm.dbg.value(metadata, metadata, metadata)
!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!5, !6, !7, !8}
!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !3, producer: "Me", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: null, retainedTypes: null, imports: null)
!1 = !DILocalVariable(name: "", arg: 1, scope: !2, file: null, line: 1, type: null)
!2 = distinct !DISubprogram(name: "debug", linkageName: "debug", scope: null, file: null, line: 0, type: null, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: true, unit: !0)
!3 = !DIFile(filename: "consecutive-fences.ll", directory: "")
!5 = !{i32 2, !"Dwarf Version", i32 4}
!6 = !{i32 2, !"Debug Info Version", i32 3}
!7 = !{i32 1, !"wchar_size", i32 4}
!8 = !{i32 7, !"PIC Level", i32 2}
!9 = !DILocation(line: 0, column: 0, scope: !2)