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[NFC][SimplifyCFG] Make 'conditional block' handling more straight-forward

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This will simplify making use of profile weights
to not perform the speculation when obviously unprofitable.
This commit is contained in:
Roman Lebedev 2021-07-23 23:10:46 +03:00
parent 4b1e13b415
commit 14b3a6d1a9
1 changed files with 17 additions and 30 deletions
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47
lib/Transforms/Utils/SimplifyCFG.cpp
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@ -2716,6 +2716,14 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
if (isa<ConstantInt>(IfCond)) if (isa<ConstantInt>(IfCond))
return false; return false;
BasicBlock *DomBlock = DomBI->getParent();
SmallVector<BasicBlock *, 2> IfBlocks;
llvm::copy_if(
PN->blocks(), std::back_inserter(IfBlocks), [](BasicBlock *IfBlock) {
return cast<BranchInst>(IfBlock->getTerminator())->isUnconditional();
});
assert(!IfBlocks.empty() && "Will have at least one block to speculate.");
// Don't try to fold an unreachable block. For example, the phi node itself // Don't try to fold an unreachable block. For example, the phi node itself
// can't be the candidate if-condition for a select that we want to form. // can't be the candidate if-condition for a select that we want to form.
if (auto *IfCondPhiInst = dyn_cast<PHINode>(IfCond)) if (auto *IfCondPhiInst = dyn_cast<PHINode>(IfCond))
@ -2794,13 +2802,8 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
// in the predecessor blocks can be promoted as well. If not, we won't be able // in the predecessor blocks can be promoted as well. If not, we won't be able
// to get rid of the control flow, so it's not worth promoting to select // to get rid of the control flow, so it's not worth promoting to select
// instructions. // instructions.
BasicBlock *DomBlock = DomBI->getParent(); for (BasicBlock *IfBlock : IfBlocks)
BasicBlock *IfBlock1 = PN->getIncomingBlock(0); for (BasicBlock::iterator I = IfBlock->begin(); !I->isTerminator(); ++I)
BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
IfBlock1 = nullptr;
} else {
for (BasicBlock::iterator I = IfBlock1->begin(); !I->isTerminator(); ++I)
if (!AggressiveInsts.count(&*I) && !isa<DbgInfoIntrinsic>(I) && if (!AggressiveInsts.count(&*I) && !isa<DbgInfoIntrinsic>(I) &&
!isa<PseudoProbeInst>(I)) { !isa<PseudoProbeInst>(I)) {
// This is not an aggressive instruction that we can promote. // This is not an aggressive instruction that we can promote.
@ -2808,24 +2811,10 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
// the xform is not worth it. // the xform is not worth it.
return Changed; return Changed;
} }
}
if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
IfBlock2 = nullptr;
} else {
for (BasicBlock::iterator I = IfBlock2->begin(); !I->isTerminator(); ++I)
if (!AggressiveInsts.count(&*I) && !isa<DbgInfoIntrinsic>(I) &&
!isa<PseudoProbeInst>(I)) {
// This is not an aggressive instruction that we can promote.
// Because of this, we won't be able to get rid of the control flow, so
// the xform is not worth it.
return Changed;
}
}
// If either of the blocks has it's address taken, we can't do this fold. // If either of the blocks has it's address taken, we can't do this fold.
if ((IfBlock1 && IfBlock1->hasAddressTaken()) || if (any_of(IfBlocks,
(IfBlock2 && IfBlock2->hasAddressTaken())) [](BasicBlock *IfBlock) { return IfBlock->hasAddressTaken(); }))
return Changed; return Changed;
LLVM_DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond LLVM_DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond
@ -2837,10 +2826,8 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
// Move all 'aggressive' instructions, which are defined in the // Move all 'aggressive' instructions, which are defined in the
// conditional parts of the if's up to the dominating block. // conditional parts of the if's up to the dominating block.
if (IfBlock1) for (BasicBlock *IfBlock : IfBlocks)
hoistAllInstructionsInto(DomBlock, DomBI, IfBlock1); hoistAllInstructionsInto(DomBlock, DomBI, IfBlock);
if (IfBlock2)
hoistAllInstructionsInto(DomBlock, DomBI, IfBlock2);
IRBuilder<NoFolder> Builder(DomBI); IRBuilder<NoFolder> Builder(DomBI);
// Propagate fast-math-flags from phi nodes to replacement selects. // Propagate fast-math-flags from phi nodes to replacement selects.
@ -2850,8 +2837,8 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
Builder.setFastMathFlags(PN->getFastMathFlags()); Builder.setFastMathFlags(PN->getFastMathFlags());
// Change the PHI node into a select instruction. // Change the PHI node into a select instruction.
Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse); Value *TrueVal = PN->getIncomingValueForBlock(IfTrue);
Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue); Value *FalseVal = PN->getIncomingValueForBlock(IfFalse);
Value *Sel = Builder.CreateSelect(IfCond, TrueVal, FalseVal, "", DomBI); Value *Sel = Builder.CreateSelect(IfCond, TrueVal, FalseVal, "", DomBI);
PN->replaceAllUsesWith(Sel); PN->replaceAllUsesWith(Sel);
@ -2859,7 +2846,7 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
PN->eraseFromParent(); PN->eraseFromParent();
} }
// At this point, IfBlock1 and IfBlock2 are both empty, so our if statement // At this point, all IfBlocks are empty, so our if statement
// has been flattened. Change DomBlock to jump directly to our new block to // has been flattened. Change DomBlock to jump directly to our new block to
// avoid other simplifycfg's kicking in on the diamond. // avoid other simplifycfg's kicking in on the diamond.
Builder.CreateBr(BB); Builder.CreateBr(BB);