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Promote shifts by a constant to multiplies so that we can reassociate 

(x<<1)+(y<<1) -> (X+Y)<<1.  This implements
Transforms/Reassociate/shift-factor.ll

llvm-svn: 26753
This commit is contained in:
Chris Lattner 2006-03-14 06:55:18 +00:00
parent c714f268bf
commit d6bde46d85
1 changed files with 17 additions and 13 deletions
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30
llvm/lib/Transforms/Scalar/Reassociate.cpp
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@ -410,19 +410,23 @@ static Instruction *BreakUpSubtract(Instruction *Sub) {
/// by one, change this into a multiply by a constant to assist with further
/// reassociation.
static Instruction *ConvertShiftToMul(Instruction *Shl) {
if (!isReassociableOp(Shl->getOperand(0), Instruction::Mul) &&
!(Shl->hasOneUse() && isReassociableOp(Shl->use_back(),Instruction::Mul)))
return 0;
Constant *MulCst = ConstantInt::get(Shl->getType(), 1);
MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1)));
std::string Name = Shl->getName(); Shl->setName("");
Instruction *Mul = BinaryOperator::createMul(Shl->getOperand(0), MulCst,
Name, Shl);
Shl->replaceAllUsesWith(Mul);
Shl->eraseFromParent();
return Mul;
// If an operand of this shift is a reassociable multiply, or if the shift
// is used by a reassociable multiply or add, turn into a multiply.
if (isReassociableOp(Shl->getOperand(0), Instruction::Mul) ||
(Shl->hasOneUse() &&
(isReassociableOp(Shl->use_back(), Instruction::Mul) ||
isReassociableOp(Shl->use_back(), Instruction::Add)))) {
Constant *MulCst = ConstantInt::get(Shl->getType(), 1);
MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1)));
std::string Name = Shl->getName(); Shl->setName("");
Instruction *Mul = BinaryOperator::createMul(Shl->getOperand(0), MulCst,
Name, Shl);
Shl->replaceAllUsesWith(Mul);
Shl->eraseFromParent();
return Mul;
}
return 0;
}
// Scan backwards and forwards among values with the same rank as element i to