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PHINode::getBasicBlockIndex is O(n) in the number of inputs

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to a PHI, avoid it in the common case where the BB occurs
in the same index for multiple phis.  This speeds up CGP on
an insane testcase from 8.35 to 3.58s.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@96080 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-02-13 04:24:19 +00:00
parent 2f36ea8b74
commit 277cccc58f
1 changed files with 10 additions and 3 deletions
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13
lib/Transforms/Utils/BreakCriticalEdges.cpp
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@ -179,7 +179,7 @@ BasicBlock *llvm::SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum,
// Create a new basic block, linking it into the CFG.
BasicBlock *NewBB = BasicBlock::Create(TI->getContext(),
TIBB->getName() + "." + DestBB->getName() + "_crit_edge");
// Create our unconditional branch...
// Create our unconditional branch.
BranchInst::Create(DestBB, NewBB);
// Branch to the new block, breaking the edge.
@ -193,12 +193,19 @@ BasicBlock *llvm::SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum,
// If there are any PHI nodes in DestBB, we need to update them so that they
// merge incoming values from NewBB instead of from TIBB.
//
unsigned BBIdx = 0;
for (BasicBlock::iterator I = DestBB->begin(); isa<PHINode>(I); ++I) {
PHINode *PN = cast<PHINode>(I);
// We no longer enter through TIBB, now we come in through NewBB. Revector
// exactly one entry in the PHI node that used to come from TIBB to come
// from NewBB.
int BBIdx = PN->getBasicBlockIndex(TIBB);
PHINode *PN = cast<PHINode>(I);
// Reuse the previous value of BBIdx if it lines up. In cases where we have
// multiple phi nodes with *lots* of predecessors, this is a speed win
// because we don't have to scan the PHI looking for TIBB. This happens
// because the BB list of PHI nodes are usually in the same order.
if (PN->getIncomingBlock(BBIdx) != TIBB)
BBIdx = PN->getBasicBlockIndex(TIBB);
PN->setIncomingBlock(BBIdx, NewBB);
}