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more refactoring. Use early exits instead of really complex logic.

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No functionality change.

llvm-svn: 53532
This commit is contained in:
Chris Lattner 2008-07-13 22:04:41 +00:00
parent a4a80e0092
commit 7cb257551f
1 changed files with 98 additions and 109 deletions
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207
lib/Transforms/Utils/SimplifyCFG.cpp
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@ -1561,121 +1561,110 @@ static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
// If this is a conditional branch in an empty block, and if any
// predecessors is a conditional branch to one of our destinations,
// fold the conditions into logical ops and one cond br.
if (&BB->front() == BI) {
int PBIOp, BIOp;
if (PBI->getSuccessor(0) == BI->getSuccessor(0)) {
PBIOp = BIOp = 0;
} else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) {
PBIOp = 0; BIOp = 1;
} else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) {
PBIOp = 1; BIOp = 0;
} else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) {
PBIOp = BIOp = 1;
} else {
PBIOp = BIOp = -1;
}
if (&BB->front() != BI)
return false;
int PBIOp, BIOp;
if (PBI->getSuccessor(0) == BI->getSuccessor(0))
PBIOp = BIOp = 0;
else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
PBIOp = 0, BIOp = 1;
else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
PBIOp = 1, BIOp = 0;
else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
PBIOp = BIOp = 1;
else
return false;
// Check to make sure that the other destination of this branch
// isn't BB itself. If so, this is an infinite loop that will
// keep getting unwound.
if (PBIOp != -1 && PBI->getSuccessor(PBIOp) == BB)
PBIOp = BIOp = -1;
// Check to make sure that the other destination of this branch
// isn't BB itself. If so, this is an infinite loop that will
// keep getting unwound.
if (PBI->getSuccessor(PBIOp) == BB)
return false;
// Do not perform this transformation if it would require
// insertion of a large number of select instructions. For targets
// without predication/cmovs, this is a big pessimization.
if (PBIOp != -1) {
BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
// Do not perform this transformation if it would require
// insertion of a large number of select instructions. For targets
// without predication/cmovs, this is a big pessimization.
BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
unsigned NumPhis = 0;
for (BasicBlock::iterator II = CommonDest->begin();
isa<PHINode>(II); ++II, ++NumPhis) {
if (NumPhis > 2) {
// Disable this xform.
PBIOp = -1;
break;
}
}
}
unsigned NumPhis = 0;
for (BasicBlock::iterator II = CommonDest->begin();
isa<PHINode>(II); ++II, ++NumPhis)
if (NumPhis > 2) // Disable this xform.
return false;
// Finally, if everything is ok, fold the branches to logical ops.
if (PBIOp != -1) {
BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
// If OtherDest *is* BB, then this is a basic block with just
// a conditional branch in it, where one edge (OtherDesg) goes
// back to the block. We know that the program doesn't get
// stuck in the infinite loop, so the condition must be such
// that OtherDest isn't branched through. Forward to CommonDest,
// and avoid an infinite loop at optimizer time.
if (OtherDest == BB)
OtherDest = CommonDest;
DOUT << "FOLDING BRs:" << *PBI->getParent()
<< "AND: " << *BI->getParent();
DOUT << *PBI->getParent()->getParent();
// BI may have other predecessors. Because of this, we leave
// it alone, but modify PBI.
// Make sure we get to CommonDest on True&True directions.
Value *PBICond = PBI->getCondition();
if (PBIOp)
PBICond = BinaryOperator::CreateNot(PBICond,
PBICond->getName()+".not",
PBI);
Value *BICond = BI->getCondition();
if (BIOp)
BICond = BinaryOperator::CreateNot(BICond,
BICond->getName()+".not",
PBI);
// Merge the conditions.
Value *Cond =
BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
// Modify PBI to branch on the new condition to the new dests.
PBI->setCondition(Cond);
PBI->setSuccessor(0, CommonDest);
PBI->setSuccessor(1, OtherDest);
// OtherDest may have phi nodes. If so, add an entry from PBI's
// block that are identical to the entries for BI's block.
PHINode *PN;
for (BasicBlock::iterator II = OtherDest->begin();
(PN = dyn_cast<PHINode>(II)); ++II) {
Value *V = PN->getIncomingValueForBlock(BB);
PN->addIncoming(V, PBI->getParent());
}
// We know that the CommonDest already had an edge from PBI to
// it. If it has PHIs though, the PHIs may have different
// entries for BB and PBI's BB. If so, insert a select to make
// them agree.
for (BasicBlock::iterator II = CommonDest->begin();
(PN = dyn_cast<PHINode>(II)); ++II) {
Value *BIV = PN->getIncomingValueForBlock(BB);
unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
Value *PBIV = PN->getIncomingValue(PBBIdx);
if (BIV != PBIV) {
// Insert a select in PBI to pick the right value.
Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
PBIV->getName()+".mux", PBI);
PN->setIncomingValue(PBBIdx, NV);
}
}
DOUT << "INTO: " << *PBI->getParent();
DOUT << *PBI->getParent()->getParent();
// This basic block is probably dead. We know it has at least
// one fewer predecessor.
return true;
// Finally, if everything is ok, fold the branches to logical ops.
BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
// If OtherDest *is* BB, then this is a basic block with just
// a conditional branch in it, where one edge (OtherDesg) goes
// back to the block. We know that the program doesn't get
// stuck in the infinite loop, so the condition must be such
// that OtherDest isn't branched through. Forward to CommonDest,
// and avoid an infinite loop at optimizer time.
if (OtherDest == BB)
OtherDest = CommonDest;
DOUT << "FOLDING BRs:" << *PBI->getParent()
<< "AND: " << *BI->getParent();
DOUT << *PBI->getParent()->getParent();
// BI may have other predecessors. Because of this, we leave
// it alone, but modify PBI.
// Make sure we get to CommonDest on True&True directions.
Value *PBICond = PBI->getCondition();
if (PBIOp)
PBICond = BinaryOperator::CreateNot(PBICond,
PBICond->getName()+".not",
PBI);
Value *BICond = BI->getCondition();
if (BIOp)
BICond = BinaryOperator::CreateNot(BICond,
BICond->getName()+".not",
PBI);
// Merge the conditions.
Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
// Modify PBI to branch on the new condition to the new dests.
PBI->setCondition(Cond);
PBI->setSuccessor(0, CommonDest);
PBI->setSuccessor(1, OtherDest);
// OtherDest may have phi nodes. If so, add an entry from PBI's
// block that are identical to the entries for BI's block.
PHINode *PN;
for (BasicBlock::iterator II = OtherDest->begin();
(PN = dyn_cast<PHINode>(II)); ++II) {
Value *V = PN->getIncomingValueForBlock(BB);
PN->addIncoming(V, PBI->getParent());
}
// We know that the CommonDest already had an edge from PBI to
// it. If it has PHIs though, the PHIs may have different
// entries for BB and PBI's BB. If so, insert a select to make
// them agree.
for (BasicBlock::iterator II = CommonDest->begin();
(PN = dyn_cast<PHINode>(II)); ++II) {
Value *BIV = PN->getIncomingValueForBlock(BB);
unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
Value *PBIV = PN->getIncomingValue(PBBIdx);
if (BIV != PBIV) {
// Insert a select in PBI to pick the right value.
Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
PBIV->getName()+".mux", PBI);
PN->setIncomingValue(PBBIdx, NV);
}
}
return false;
DOUT << "INTO: " << *PBI->getParent();
DOUT << *PBI->getParent()->getParent();
// This basic block is probably dead. We know it has at least
// one fewer predecessor.
return true;
}