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[SimplifyCFG] SimplifyTerminatorOnSelect(): fix/tune DomTree updates

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We only need to remove non-TrueBB/non-FalseBB successors,
and we only need to do that once. We don't need to insert
any new edges, because no new successors will be added.
This commit is contained in:
Roman Lebedev 2021-01-03 21:17:11 +03:00
parent 73135b2e1f
commit 9748fdf56f
2 changed files with 14 additions and 11 deletions
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23
lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -3849,7 +3849,6 @@ bool SimplifyCFGOpt::SimplifyTerminatorOnSelect(Instruction *OldTerm,
uint32_t TrueWeight,
uint32_t FalseWeight) {
auto *BB = OldTerm->getParent();
// Remove any superfluous successor edges from the CFG.
// First, figure out which successors to preserve.
// If TrueBB and FalseBB are equal, only try to preserve one copy of that
@ -3857,7 +3856,7 @@ bool SimplifyCFGOpt::SimplifyTerminatorOnSelect(Instruction *OldTerm,
BasicBlock *KeepEdge1 = TrueBB;
BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : nullptr;
SmallVector<DominatorTree::UpdateType, 4> Updates;
SmallSetVector<BasicBlock *, 2> RemovedSuccessors;
// Then remove the rest.
for (BasicBlock *Succ : successors(OldTerm)) {
@ -3869,7 +3868,9 @@ bool SimplifyCFGOpt::SimplifyTerminatorOnSelect(Instruction *OldTerm,
else {
Succ->removePredecessor(BB,
/*KeepOneInputPHIs=*/true);
Updates.push_back({DominatorTree::Delete, BB, Succ});
if (Succ != TrueBB && Succ != FalseBB)
RemovedSuccessors.insert(Succ);
}
}
@ -3882,13 +3883,10 @@ bool SimplifyCFGOpt::SimplifyTerminatorOnSelect(Instruction *OldTerm,
// We were only looking for one successor, and it was present.
// Create an unconditional branch to it.
Builder.CreateBr(TrueBB);
Updates.push_back({DominatorTree::Insert, BB, TrueBB});
} else {
// We found both of the successors we were looking for.
// Create a conditional branch sharing the condition of the select.
BranchInst *NewBI = Builder.CreateCondBr(Cond, TrueBB, FalseBB);
Updates.push_back({DominatorTree::Insert, BB, TrueBB});
Updates.push_back({DominatorTree::Insert, BB, FalseBB});
if (TrueWeight != FalseWeight)
setBranchWeights(NewBI, TrueWeight, FalseWeight);
}
@ -3903,17 +3901,22 @@ bool SimplifyCFGOpt::SimplifyTerminatorOnSelect(Instruction *OldTerm,
if (!KeepEdge1) {
// Only TrueBB was found.
Builder.CreateBr(TrueBB);
Updates.push_back({DominatorTree::Insert, BB, TrueBB});
} else {
// Only FalseBB was found.
Builder.CreateBr(FalseBB);
Updates.push_back({DominatorTree::Insert, BB, FalseBB});
}
}
EraseTerminatorAndDCECond(OldTerm);
if (DTU)
DTU->applyUpdatesPermissive(Updates);
if (DTU) {
SmallVector<DominatorTree::UpdateType, 2> Updates;
Updates.reserve(RemovedSuccessors.size());
for (auto *RemovedSuccessor : RemovedSuccessors)
Updates.push_back({DominatorTree::Delete, BB, RemovedSuccessor});
DTU->applyUpdates(Updates);
}
return true;
}

2
test/Transforms/SimplifyCFG/SimplifyTerminatorOnSelect-domtree-preservation-edgecase.ll
View File

@ -1,5 +1,5 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -S -simplifycfg -simplifycfg-require-and-preserve-domtree=0 < %s | FileCheck %s
; RUN: opt -S -simplifycfg -simplifycfg-require-and-preserve-domtree=1 < %s | FileCheck %s
declare void @widget()
declare void @baz(i8)