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Optimize around the fact that pred_iterator is slow: instead of sorting

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PHI operands by the predecessor order, sort them by the order used by the
first PHI in the block. This is still suffucient to expose duplicates.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85634 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2009-10-30 23:15:21 +00:00
parent 9c41fa87ea
commit 1107c63efe
1 changed files with 17 additions and 15 deletions
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32
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -10981,22 +10981,24 @@ Instruction *InstCombiner::visitPHINode(PHINode &PN) {
}
}
// Sort the PHI node operands to match the pred iterator order. This will
// help identical PHIs be eliminated by other passes. Other passes shouldn't
// depend on this for correctness however.
unsigned i = 0;
for (pred_iterator PI = pred_begin(PN.getParent()),
PE = pred_end(PN.getParent()); PI != PE; ++PI, ++i)
if (PN.getIncomingBlock(i) != *PI) {
unsigned j = PN.getBasicBlockIndex(*PI);
Value *VA = PN.getIncomingValue(i);
// If there are multiple PHIs, sort their operands so that they all list
// the blocks in the same order. This will help identical PHIs be eliminated
// by other passes. Other passes shouldn't depend on this for correctness
// however.
PHINode *FirstPN = cast<PHINode>(PN.getParent()->begin());
if (&PN != FirstPN)
for (unsigned i = 0, e = FirstPN->getNumIncomingValues(); i != e; ++i) {
BasicBlock *BBA = PN.getIncomingBlock(i);
Value *VB = PN.getIncomingValue(j);
BasicBlock *BBB = PN.getIncomingBlock(j);
PN.setIncomingBlock(i, BBB);
PN.setIncomingValue(i, VB);
PN.setIncomingBlock(j, BBA);
PN.setIncomingValue(j, VA);
BasicBlock *BBB = FirstPN->getIncomingBlock(i);
if (BBA != BBB) {
Value *VA = PN.getIncomingValue(i);
unsigned j = FirstPN->getBasicBlockIndex(BBA);
Value *VB = PN.getIncomingValue(j);
PN.setIncomingBlock(i, BBB);
PN.setIncomingValue(i, VB);
PN.setIncomingBlock(j, BBA);
PN.setIncomingValue(j, VA);
}
}
return 0;