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[SimplifyCFG] Fix a debug invariant bug in FoldBranchToCommonDest()

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Summary:
Fix a case where FoldBranchToCommonDest() would bail out from doing CSE
when encountering a debug intrinsic. Handle that by skipping past the
debug intrinsics.

Also, as a minor refactoring, rename checkCSEInPredecessor() to
tryCSEWithPredecessor() to make it a bit more clear that the function
may remove instructions.

Reviewers: fhahn, craig.topper, dblaikie, xbolva00

Reviewed By: fhahn, xbolva00

Subscribers: vsk, davide, llvm-commits

Differential Revision: https://reviews.llvm.org/D46635

llvm-svn: 332698
This commit is contained in:
David Stenberg 2018-05-18 08:52:15 +00:00
parent da3f49a435
commit 0af67e5b65
2 changed files with 54 additions and 3 deletions
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8
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -2498,7 +2498,7 @@ static bool SimplifyCondBranchToTwoReturns(BranchInst *BI,
/// Return true if the given instruction is available
/// in its predecessor block. If yes, the instruction will be removed.
static bool checkCSEInPredecessor(Instruction *Inst, BasicBlock *PB) {
static bool tryCSEWithPredecessor(Instruction *Inst, BasicBlock *PB) {
if (!isa<BinaryOperator>(Inst) && !isa<CmpInst>(Inst))
return false;
for (Instruction &I : *PB) {
@ -2555,14 +2555,16 @@ bool llvm::FoldBranchToCommonDest(BranchInst *BI, unsigned BonusInstThreshold) {
if (PBI->isConditional() &&
(BI->getSuccessor(0) == PBI->getSuccessor(0) ||
BI->getSuccessor(0) == PBI->getSuccessor(1))) {
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;) {
for (auto I = BB->instructionsWithoutDebug().begin(),
E = BB->instructionsWithoutDebug().end();
I != E;) {
Instruction *Curr = &*I++;
if (isa<CmpInst>(Curr)) {
Cond = Curr;
break;
}
// Quit if we can't remove this instruction.
if (!checkCSEInPredecessor(Curr, PB))
if (!tryCSEWithPredecessor(Curr, PB))
return false;
}
}

49
llvm/test/Transforms/SimplifyCFG/fold-branch-debuginvariant.ll Normal file
View File

@ -0,0 +1,49 @@
; RUN: opt < %s -simplifycfg -S | FileCheck %s
; RUN: opt < %s -strip-debug -simplifycfg -S | FileCheck %s
; Verify that the and.2 instruction is eliminated even in the presence of a
; preceding debug intrinsic.
; CHECK-LABEL: bb1:
; CHECK: and i1 false, false
; CHECK-LABEL: bb2:
; CHECK-NOT: and i1 false, false
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
; Function Attrs: norecurse nounwind
define void @foo() local_unnamed_addr #0 !dbg !4 {
bb1:
%and.1 = and i1 false, false
%cmp = icmp eq i16 0, 0
br i1 %cmp, label %bb2, label %bb3
bb2: ; preds = %bb1
call void @llvm.dbg.value(metadata i16 0, metadata !8, metadata !DIExpression()), !dbg !9
%and.2 = and i1 false, false
br label %bb3
bb3: ; preds = %bb2, %bb1
ret void
}
; Function Attrs: nounwind readnone speculatable
declare void @llvm.dbg.value(metadata, metadata, metadata) #1
attributes #0 = { norecurse nounwind }
attributes #1 = { nounwind readnone speculatable }
!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!3}
!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "Foo", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !2, globals: !2)
!1 = !DIFile(filename: "foo.c", directory: "/")
!2 = !{}
!3 = !{i32 2, !"Debug Info Version", i32 3}
!4 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 10, type: !5, isLocal: false, isDefinition: true, scopeLine: 10, isOptimized: false, unit: !0, retainedNodes: !2)
!5 = !DISubroutineType(types: !6)
!6 = !{null, !7}
!7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
!8 = !DILocalVariable(name: "p_1", arg: 1, scope: !4, line: 4, type: !7)
!9 = distinct !DILocation(line: 11, column: 3, scope: !4)