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[SimplifyCFG] Teach tryWidenCondBranchToCondBranch() to preserve DomTree

This commit is contained in:
Roman Lebedev 2021-01-01 16:33:19 +03:00
parent e08fea3b24
commit f1ce696056
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GPG Key ID: 083C3EBB4A1689E0
2 changed files with 16 additions and 5 deletions
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19
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -3530,7 +3530,8 @@ static bool mergeConditionalStores(BranchInst *PBI, BranchInst *QBI,
/// If the previous block ended with a widenable branch, determine if reusing
/// the target block is profitable and legal. This will have the effect of
/// "widening" PBI, but doesn't require us to reason about hosting safety.
static bool tryWidenCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
static bool tryWidenCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI,
DomTreeUpdater *DTU) {
// TODO: This can be generalized in two important ways:
// 1) We can allow phi nodes in IfFalseBB and simply reuse all the input
// values from the PBI edge.
@ -3553,15 +3554,25 @@ static bool tryWidenCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
if (BI->getSuccessor(1) != IfFalseBB && // no inf looping
BI->getSuccessor(1)->getTerminatingDeoptimizeCall() && // profitability
NoSideEffects(*BI->getParent())) {
BI->getSuccessor(1)->removePredecessor(BI->getParent());
auto *OldSuccessor = BI->getSuccessor(1);
OldSuccessor->removePredecessor(BI->getParent());
BI->setSuccessor(1, IfFalseBB);
if (DTU)
DTU->applyUpdatesPermissive(
{{DominatorTree::Delete, BI->getParent(), OldSuccessor},
{DominatorTree::Insert, BI->getParent(), IfFalseBB}});
return true;
}
if (BI->getSuccessor(0) != IfFalseBB && // no inf looping
BI->getSuccessor(0)->getTerminatingDeoptimizeCall() && // profitability
NoSideEffects(*BI->getParent())) {
BI->getSuccessor(0)->removePredecessor(BI->getParent());
auto *OldSuccessor = BI->getSuccessor(0);
OldSuccessor->removePredecessor(BI->getParent());
BI->setSuccessor(0, IfFalseBB);
if (DTU)
DTU->applyUpdatesPermissive(
{{DominatorTree::Delete, BI->getParent(), OldSuccessor},
{DominatorTree::Insert, BI->getParent(), IfFalseBB}});
return true;
}
return false;
@ -3626,7 +3637,7 @@ static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI,
// If the previous block ended with a widenable branch, determine if reusing
// the target block is profitable and legal. This will have the effect of
// "widening" PBI, but doesn't require us to reason about hosting safety.
if (tryWidenCondBranchToCondBranch(PBI, BI))
if (tryWidenCondBranchToCondBranch(PBI, BI, DTU))
return true;
if (auto *CE = dyn_cast<ConstantExpr>(BI->getCondition()))

2
llvm/test/Transforms/SimplifyCFG/wc-widen-block.ll
View File

@ -1,5 +1,5 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -passes=simplify-cfg -S < %s | FileCheck %s
; RUN: opt -passes=simplify-cfg -simplifycfg-require-and-preserve-domtree=1 -S < %s | FileCheck %s
define i32 @basic(i1 %cond_0, i32* %p) {
; CHECK-LABEL: @basic(