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Export ConstantFoldTerminator, allow it to fold conditional branches to

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the same label.

llvm-svn: 107
This commit is contained in:
Chris Lattner 2001-06-29 23:56:58 +00:00
parent 10b250eb4d
commit 7ce8b17e60
1 changed files with 30 additions and 8 deletions
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38
llvm/lib/Transforms/Scalar/ConstantProp.cpp
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@ -120,28 +120,50 @@ ConstantFoldBinaryInst(Method *M, Method::inst_iterator &DI,
return true;
}
inline static bool ConstantFoldTerminator(TerminatorInst *T) {
// ConstantFoldTerminator - If a terminator instruction is predicated on a
// constant value, convert it into an unconditional branch to the constant
// destination.
//
bool ConstantFoldTerminator(TerminatorInst *T) {
// Branch - See if we are conditional jumping on constant
if (T->getInstType() == Instruction::Br) {
BranchInst *BI = (BranchInst*)T;
if (!BI->isUnconditional() && // Are we branching on constant?
BI->getOperand(2)->isConstant()) {
if (BI->isUnconditional()) return false; // Can't optimize uncond branch
BasicBlock *Dest1 = BI->getOperand(0)->castBasicBlockAsserting();
BasicBlock *Dest2 = BI->getOperand(1)->castBasicBlockAsserting();
if (BI->getOperand(2)->isConstant()) { // Are we branching on constant?
// YES. Change to unconditional branch...
ConstPoolBool *Cond = (ConstPoolBool*)BI->getOperand(2);
Value *Destination = BI->getOperand(Cond->getValue() ? 0 : 1);
Value *OldDest = BI->getOperand(Cond->getValue() ? 1 : 0);
BasicBlock *Destination = Cond->getValue() ? Dest1 : Dest2;
BasicBlock *OldDest = Cond->getValue() ? Dest2 : Dest1;
//cerr << "Method: " << T->getParent()->getParent() << "\nRemoving branch from " << T->getParent() << "\n\nTo: " << OldDest << endl;
//cerr << "Method: " << T->getParent()->getParent()
// << "\nRemoving branch from " << T->getParent()
// << "\n\nTo: " << OldDest << endl;
// Let the basic block know that we are letting go of it. Based on this,
// it will adjust it's PHI nodes.
assert(T->getParent() && "Terminator not inserted in block!");
OldDest->castBasicBlockAsserting()->removePredecessor(T->getParent());
assert(BI->getParent() && "Terminator not inserted in block!");
OldDest->removePredecessor(BI->getParent());
BI->setOperand(0, Destination); // Set the unconditional destination
BI->setOperand(1, 0); // Clear the conditional destination
BI->setOperand(2, 0); // Clear the condition...
return true;
} else if (Dest2 == Dest1) { // Conditional branch to same location?
// This branch matches something like this:
// br bool %cond, label %Dest, label %Dest
// and changes it into: br label %Dest
// Let the basic block know that we are letting go of one copy of it.
assert(BI->getParent() && "Terminator not inserted in block!");
Dest1->removePredecessor(BI->getParent());
// Nuke the second destination, and the use of the condition variable
BI->setOperand(1, 0); // Clear the conditional destination
BI->setOperand(2, 0); // Clear the condition...
return true;
}
}
return false;