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make the logic for breaking up subtracts more explicit, no

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functionality change.

llvm-svn: 47239
This commit is contained in:
Chris Lattner 2008-02-17 20:44:51 +00:00
parent 03755061ae
commit cd6f9cea98
1 changed files with 22 additions and 9 deletions
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31
lib/Transforms/Scalar/Reassociate.cpp
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@ -391,17 +391,30 @@ static Value *NegateValue(Value *V, Instruction *BI) {
return BinaryOperator::createNeg(V, V->getName() + ".neg", BI);
}
/// ShouldBreakUpSubtract - Return true if we should break up this subtract of
/// X-Y into (X + -Y).
static bool ShouldBreakUpSubtract(Instruction *Sub) {
// If this is a negation, we can't split it up!
if (BinaryOperator::isNeg(Sub))
return false;
// Don't bother to break this up unless either the LHS is an associable add or
// if this is only used by one.
if (isReassociableOp(Sub->getOperand(0), Instruction::Add))
return true;
if (isReassociableOp(Sub->getOperand(1), Instruction::Add))
return true;
if (Sub->hasOneUse() && isReassociableOp(Sub->use_back(), Instruction::Add))
return true;
return false;
}
/// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is
/// only used by an add, transform this into (X+(0-Y)) to promote better
/// reassociation.
static Instruction *BreakUpSubtract(Instruction *Sub) {
// Don't bother to break this up unless either the LHS is an associable add or
// if this is only used by one.
if (!isReassociableOp(Sub->getOperand(0), Instruction::Add) &&
!isReassociableOp(Sub->getOperand(1), Instruction::Add) &&
!(Sub->hasOneUse() &&isReassociableOp(Sub->use_back(), Instruction::Add)))
return 0;
// Convert a subtract into an add and a neg instruction... so that sub
// instructions can be commuted with other add instructions...
//
@ -762,12 +775,12 @@ void Reassociate::ReassociateBB(BasicBlock *BB) {
// If this is a subtract instruction which is not already in negate form,
// see if we can convert it to X+-Y.
if (BI->getOpcode() == Instruction::Sub) {
if (!BinaryOperator::isNeg(BI)) {
if (ShouldBreakUpSubtract(BI)) {
if (Instruction *NI = BreakUpSubtract(BI)) {
MadeChange = true;
BI = NI;
}
} else {
} else if (BinaryOperator::isNeg(BI)) {
// Otherwise, this is a negation. See if the operand is a multiply tree
// and if this is not an inner node of a multiply tree.
if (isReassociableOp(BI->getOperand(1), Instruction::Mul) &&