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Implement SimplifyCFG/branch-cond-merge.ll

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Turning "if (A < B && B < C)" into "if (A < B & B < C)"

llvm-svn: 13311
This commit is contained in:
Chris Lattner 2004-05-01 23:35:43 +00:00
parent c8991cdae8
commit bd705d7776
1 changed files with 64 additions and 10 deletions
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58
lib/Transforms/Utils/SimplifyCFG.cpp
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@ -790,7 +790,8 @@ bool llvm::SimplifyCFG(BasicBlock *BB) {
if (FoldValueComparisonIntoPredecessors(SI))
return SimplifyCFG(BB) || 1;
} else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
if (Value *CompVal = isValueEqualityComparison(BB->getTerminator())) {
if (BI->isConditional()) {
if (Value *CompVal = isValueEqualityComparison(BI)) {
// This block must be empty, except for the setcond inst, if it exists.
BasicBlock::iterator I = BB->begin();
if (&*I == BI ||
@ -800,7 +801,60 @@ bool llvm::SimplifyCFG(BasicBlock *BB) {
return SimplifyCFG(BB) | true;
}
if (BI->isConditional()) {
// If this basic block is ONLY a setcc and a branch, and if a predecessor
// branches to us and one of our successors, fold the setcc into the
// predecessor and use logical operations to pick the right destination.
if (Instruction *Cond = dyn_cast<Instruction>(BI->getCondition()))
if (Cond->getParent() == BB && &BB->front() == Cond &&
Cond->getNext() == BI && Cond->hasOneUse()) {
BasicBlock *TrueDest = BI->getSuccessor(0);
BasicBlock *FalseDest = BI->getSuccessor(1);
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI!=E; ++PI)
if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
if (PBI->isConditional()) {
if (PBI->getSuccessor(0) == FalseDest ||
PBI->getSuccessor(1) == TrueDest) {
// Invert the predecessors condition test (xor it with true),
// which allows us to write this code once.
Value *NewCond =
BinaryOperator::createNot(PBI->getCondition(),
PBI->getCondition()->getName()+".not", PBI);
PBI->setCondition(NewCond);
BasicBlock *OldTrue = PBI->getSuccessor(0);
BasicBlock *OldFalse = PBI->getSuccessor(1);
PBI->setSuccessor(0, OldFalse);
PBI->setSuccessor(1, OldTrue);
}
if (PBI->getSuccessor(0) == TrueDest ||
PBI->getSuccessor(1) == FalseDest) {
// Clone Cond into the predecessor basic block, and and the
// two conditions together.
Instruction *New = Cond->clone();
New->setName(Cond->getName());
Cond->setName(Cond->getName()+".old");
(*PI)->getInstList().insert(PBI, New);
Instruction::BinaryOps Opcode =
PBI->getSuccessor(0) == TrueDest ?
Instruction::Or : Instruction::And;
Value *NewCond =
BinaryOperator::create(Opcode, PBI->getCondition(),
New, "bothcond", PBI);
PBI->setCondition(NewCond);
if (PBI->getSuccessor(0) == BB) {
AddPredecessorToBlock(TrueDest, *PI, BB);
PBI->setSuccessor(0, TrueDest);
}
if (PBI->getSuccessor(1) == BB) {
AddPredecessorToBlock(FalseDest, *PI, BB);
PBI->setSuccessor(1, FalseDest);
}
return SimplifyCFG(BB) | 1;
}
}
}
// If this block ends with a branch instruction, and if there is one
// predecessor, see if the previous block ended with a branch on the same
// condition, which makes this conditional branch redundant.