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[SimplifyCFG] Teach SimplifyCondBranchToCondBranch() to preserve DomTree

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This commit is contained in:
Roman Lebedev 2020-12-30 00:21:32 +03:00
parent e0ffb58a76
commit d0d3ccbc30
4 changed files with 15 additions and 3 deletions
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12
lib/Transforms/Utils/SimplifyCFG.cpp
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@ -3668,6 +3668,8 @@ static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI,
LLVM_DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
<< "AND: " << *BI->getParent());
SmallVector<DominatorTree::UpdateType, 5> Updates;
// If OtherDest *is* BB, then BB is a basic block with a single conditional
// branch in it, where one edge (OtherDest) goes back to itself but the other
// exits. We don't *know* that the program avoids the infinite loop
@ -3681,6 +3683,7 @@ static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI,
BasicBlock *InfLoopBlock =
BasicBlock::Create(BB->getContext(), "infloop", BB->getParent());
BranchInst::Create(InfLoopBlock, InfLoopBlock);
Updates.push_back({DominatorTree::Insert, InfLoopBlock, InfLoopBlock});
OtherDest = InfLoopBlock;
}
@ -3702,11 +3705,20 @@ static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI,
// Merge the conditions.
Value *Cond = Builder.CreateOr(PBICond, BICond, "brmerge");
for (auto *Successor : successors(PBI->getParent()))
Updates.push_back({DominatorTree::Delete, PBI->getParent(), Successor});
// Modify PBI to branch on the new condition to the new dests.
PBI->setCondition(Cond);
PBI->setSuccessor(0, CommonDest);
PBI->setSuccessor(1, OtherDest);
for (auto *Successor : successors(PBI->getParent()))
Updates.push_back({DominatorTree::Insert, PBI->getParent(), Successor});
if (DTU)
DTU->applyUpdatesPermissive(Updates);
// Update branch weight for PBI.
uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
uint64_t PredCommon, PredOther, SuccCommon, SuccOther;

2
test/Transforms/SimplifyCFG/2008-07-13-InfLoopMiscompile.ll
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@ -1,5 +1,5 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -simplifycfg -S | FileCheck %s
; RUN: opt < %s -simplifycfg -simplifycfg-require-and-preserve-domtree=1 -S | FileCheck %s
; PR2540
; Outval should end up with a select from 0/2, not all constants.

2
test/Transforms/SimplifyCFG/extract-cost.ll
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@ -1,5 +1,5 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -simplifycfg -S < %s | FileCheck %s
; RUN: opt -simplifycfg -simplifycfg-require-and-preserve-domtree=1 -S < %s | FileCheck %s
declare { i32, i1 } @llvm.uadd.with.overflow.i32(i32, i32) #1

2
test/Transforms/SimplifyCFG/pr34131.ll
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@ -1,4 +1,4 @@
; RUN: opt -simplifycfg -S < %s | FileCheck %s
; RUN: opt -simplifycfg -simplifycfg-require-and-preserve-domtree=1 -S < %s | FileCheck %s
; Just checking for lack of crash here, but we should be able to check the IR?
; Earlier version using auto-generated checks from utils/update_test_checks.py