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[SimplifyCFG] Teach SimplifyBranchOnICmpChain() to preserve DomTree

This commit is contained in:
Roman Lebedev 2020-12-30 20:48:40 +03:00
parent 253dc16f9e
commit c45f765c0d
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GPG Key ID: 083C3EBB4A1689E0
2 changed files with 11 additions and 2 deletions
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11
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
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@ -4101,12 +4101,16 @@ bool SimplifyCFGOpt::SimplifyBranchOnICmpChain(BranchInst *BI,
<< " cases into SWITCH. BB is:\n"
<< *BB);
SmallVector<DominatorTree::UpdateType, 2> Updates;
// If there are any extra values that couldn't be folded into the switch
// then we evaluate them with an explicit branch first. Split the block
// right before the condbr to handle it.
if (ExtraCase) {
BasicBlock *NewBB =
BB->splitBasicBlock(BI->getIterator(), "switch.early.test");
SplitBlock(BB, BI, DTU ? &DTU->getDomTree() : nullptr, /*LI=*/nullptr,
/*MSSAU=*/nullptr, "switch.early.test");
// Remove the uncond branch added to the old block.
Instruction *OldTI = BB->getTerminator();
Builder.SetInsertPoint(OldTI);
@ -4118,6 +4122,8 @@ bool SimplifyCFGOpt::SimplifyBranchOnICmpChain(BranchInst *BI,
OldTI->eraseFromParent();
Updates.push_back({DominatorTree::Insert, BB, EdgeBB});
// If there are PHI nodes in EdgeBB, then we need to add a new entry to them
// for the edge we just added.
AddPredecessorToBlock(EdgeBB, BB, NewBB);
@ -4144,6 +4150,7 @@ bool SimplifyCFGOpt::SimplifyBranchOnICmpChain(BranchInst *BI,
// We added edges from PI to the EdgeBB. As such, if there were any
// PHI nodes in EdgeBB, they need entries to be added corresponding to
// the number of edges added.
Updates.push_back({DominatorTree::Insert, BB, EdgeBB});
for (BasicBlock::iterator BBI = EdgeBB->begin(); isa<PHINode>(BBI); ++BBI) {
PHINode *PN = cast<PHINode>(BBI);
Value *InVal = PN->getIncomingValueForBlock(BB);
@ -4153,6 +4160,8 @@ bool SimplifyCFGOpt::SimplifyBranchOnICmpChain(BranchInst *BI,
// Erase the old branch instruction.
EraseTerminatorAndDCECond(BI);
if (DTU)
DTU->applyUpdatesPermissive(Updates);
LLVM_DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
return true;

2
llvm/test/Transforms/SimplifyCFG/switch_msan.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
declare i8 @next_char();