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Split some code out to a helper function (FindReusablePredBB)

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and add a doxygen comment.

Cache the phi entry to avoid doing tons of 
PHINode::getBasicBlockIndex calls in the common case.

On my insane testcase from re2c, this speeds up CGP from
617.4s to 7.9s (78x).



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@96083 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-02-13 05:35:08 +00:00
parent 6686c6bf68
commit 98d5c3141e
1 changed files with 72 additions and 50 deletions
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122
lib/Transforms/Scalar/CodeGenPrepare.cpp
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@ -301,6 +301,70 @@ void CodeGenPrepare::EliminateMostlyEmptyBlock(BasicBlock *BB) {
DEBUG(dbgs() << "AFTER:\n" << *DestBB << "\n\n\n");
}
/// FindReusablePredBB - Check all of the predecessors of the block DestPHI
/// lives in to see if there is a block that we can reuse as a critical edge
/// from TIBB.
static BasicBlock *FindReusablePredBB(PHINode *DestPHI, BasicBlock *TIBB) {
BasicBlock *Dest = DestPHI->getParent();
/// TIPHIValues - This array is lazily computed to determine the values of
/// PHIs in Dest that TI would provide.
SmallVector<Value*, 32> TIPHIValues;
/// TIBBEntryNo - This is a cache to speed up pred queries for TIBB.
unsigned TIBBEntryNo = 0;
// Check to see if Dest has any blocks that can be used as a split edge for
// this terminator.
for (unsigned pi = 0, e = DestPHI->getNumIncomingValues(); pi != e; ++pi) {
BasicBlock *Pred = DestPHI->getIncomingBlock(pi);
// To be usable, the pred has to end with an uncond branch to the dest.
BranchInst *PredBr = dyn_cast<BranchInst>(Pred->getTerminator());
if (!PredBr || !PredBr->isUnconditional())
continue;
// Must be empty other than the branch and debug info.
BasicBlock::iterator I = Pred->begin();
while (isa<DbgInfoIntrinsic>(I))
I++;
if (&*I != PredBr)
continue;
// Cannot be the entry block; its label does not get emitted.
if (Pred == &Dest->getParent()->getEntryBlock())
continue;
// Finally, since we know that Dest has phi nodes in it, we have to make
// sure that jumping to Pred will have the same effect as going to Dest in
// terms of PHI values.
PHINode *PN;
unsigned PHINo = 0;
unsigned PredEntryNo = pi;
bool FoundMatch = true;
for (BasicBlock::iterator I = Dest->begin();
(PN = dyn_cast<PHINode>(I)); ++I, ++PHINo) {
if (PHINo == TIPHIValues.size()) {
if (PN->getIncomingBlock(TIBBEntryNo) != TIBB)
TIBBEntryNo = PN->getBasicBlockIndex(TIBB);
TIPHIValues.push_back(PN->getIncomingValue(TIBBEntryNo));
}
// If the PHI entry doesn't work, we can't use this pred.
if (PN->getIncomingBlock(PredEntryNo) != Pred)
PredEntryNo = PN->getBasicBlockIndex(Pred);
if (TIPHIValues[PHINo] != PN->getIncomingValue(PredEntryNo)) {
FoundMatch = false;
break;
}
}
// If we found a workable predecessor, change TI to branch to Succ.
if (FoundMatch)
return Pred;
}
return 0;
}
/// SplitEdgeNicely - Split the critical edge from TI to its specified
/// successor if it will improve codegen. We only do this if the successor has
@ -329,57 +393,15 @@ static void SplitEdgeNicely(TerminatorInst *TI, unsigned SuccNum,
return;
if (!FactorCommonPreds) {
/// TIPHIValues - This array is lazily computed to determine the values of
/// PHIs in Dest that TI would provide.
SmallVector<Value*, 32> TIPHIValues;
// Check to see if Dest has any blocks that can be used as a split edge for
// this terminator.
for (unsigned pi = 0, e = DestPHI->getNumIncomingValues(); pi != e; ++pi) {
BasicBlock *Pred = DestPHI->getIncomingBlock(pi);
// To be usable, the pred has to end with an uncond branch to the dest.
BranchInst *PredBr = dyn_cast<BranchInst>(Pred->getTerminator());
if (!PredBr || !PredBr->isUnconditional())
continue;
// Must be empty other than the branch and debug info.
BasicBlock::iterator I = Pred->begin();
while (isa<DbgInfoIntrinsic>(I))
I++;
if (&*I != PredBr)
continue;
// Cannot be the entry block; its label does not get emitted.
if (Pred == &Dest->getParent()->getEntryBlock())
continue;
// Finally, since we know that Dest has phi nodes in it, we have to make
// sure that jumping to Pred will have the same effect as going to Dest in
// terms of PHI values.
PHINode *PN;
unsigned PHINo = 0;
bool FoundMatch = true;
for (BasicBlock::iterator I = Dest->begin();
(PN = dyn_cast<PHINode>(I)); ++I, ++PHINo) {
if (PHINo == TIPHIValues.size())
TIPHIValues.push_back(PN->getIncomingValueForBlock(TIBB));
// If the PHI entry doesn't work, we can't use this pred.
if (TIPHIValues[PHINo] != PN->getIncomingValueForBlock(Pred)) {
FoundMatch = false;
break;
}
}
// If we found a workable predecessor, change TI to branch to Succ.
if (FoundMatch) {
ProfileInfo *PFI = P->getAnalysisIfAvailable<ProfileInfo>();
if (PFI)
PFI->splitEdge(TIBB, Dest, Pred);
Dest->removePredecessor(TIBB);
TI->setSuccessor(SuccNum, Pred);
return;
}
if (BasicBlock *ReuseBB = FindReusablePredBB(DestPHI, TIBB)) {
ProfileInfo *PFI = P->getAnalysisIfAvailable<ProfileInfo>();
if (PFI)
PFI->splitEdge(TIBB, Dest, ReuseBB);
Dest->removePredecessor(TIBB);
TI->setSuccessor(SuccNum, ReuseBB);
return;
}
SplitCriticalEdge(TI, SuccNum, P, true);
return;
}