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make FoldTwoEntryPHINode use instsimplify a bit, make

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GetIfCondition faster by avoiding pred_iterator.  No
really interesting change.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121754 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-12-14 07:00:00 +00:00
parent 2112bbc42d
commit 73c50a68a7
1 changed files with 21 additions and 12 deletions
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33
lib/Transforms/Utils/SimplifyCFG.cpp
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@ -105,20 +105,21 @@ static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
}
/// GetIfCondition - Given a basic block (BB) with two predecessors (and
/// presumably PHI nodes in it), check to see if the merge at this block is due
/// GetIfCondition - Given a basic block (BB) with two predecessors (and at
/// least one PHI node in it), check to see if the merge at this block is due
/// to an "if condition". If so, return the boolean condition that determines
/// which entry into BB will be taken. Also, return by references the block
/// that will be entered from if the condition is true, and the block that will
/// be entered if the condition is false.
///
///
static Value *GetIfCondition(BasicBlock *BB,
BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
BasicBlock *&IfFalse) {
PHINode *SomePHI = cast<PHINode>(BB->begin());
assert(SomePHI->getNumIncomingValues() == 2 &&
"Function can only handle blocks with 2 predecessors!");
BasicBlock *Pred1 = *pred_begin(BB);
BasicBlock *Pred2 = *++pred_begin(BB);
BasicBlock *Pred1 = SomePHI->getIncomingBlock(0);
BasicBlock *Pred2 = SomePHI->getIncomingBlock(1);
// We can only handle branches. Other control flow will be lowered to
// branches if possible anyway.
@ -1147,14 +1148,13 @@ static bool FoldCondBranchOnPHI(BranchInst *BI, const TargetData *TD) {
/// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
/// PHI node, see if we can eliminate it.
static bool FoldTwoEntryPHINode(PHINode *PN) {
static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD) {
// Ok, this is a two entry PHI node. Check to see if this is a simple "if
// statement", which has a very simple dominance structure. Basically, we
// are trying to find the condition that is being branched on, which
// subsequently causes this merge to happen. We really want control
// dependence information for this check, but simplifycfg can't keep it up
// to date, and this catches most of the cases we care about anyway.
//
BasicBlock *BB = PN->getParent();
BasicBlock *IfTrue, *IfFalse;
Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
@ -1247,10 +1247,19 @@ static bool FoldTwoEntryPHINode(PHINode *PN) {
Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
Value *NV;
if (Value *V = SimplifySelectInst(IfCond, TrueVal, FalseVal, TD))
NV = V;
else if (TrueVal->getType()->isIntegerTy(1) && isa<ConstantInt>(TrueVal) &&
cast<ConstantInt>(TrueVal)->isOne()) {
if (Value *V = SimplifyOrInst(IfCond, FalseVal, TD))
NV = V;
else
NV = BinaryOperator::CreateOr(IfCond, FalseVal, "", AfterPHIIt);
} else
NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
PN->replaceAllUsesWith(NV);
NV->takeName(PN);
PN->eraseFromParent();
}
return true;
@ -2415,7 +2424,7 @@ bool SimplifyCFGOpt::run(BasicBlock *BB) {
// eliminate it, do so now.
if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
if (PN->getNumIncomingValues() == 2)
Changed |= FoldTwoEntryPHINode(PN);
Changed |= FoldTwoEntryPHINode(PN, TD);
if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
if (BI->isUnconditional()) {