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Add an APInt version of ShrinkDemandedConstant.

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Patch by Zhou Sheng.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@35063 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Reid Spencer 2007-03-12 17:15:10 +00:00
parent edd089c86a
commit 6b79e2d202
1 changed files with 24 additions and 0 deletions
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24
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -1004,6 +1004,30 @@ static bool ShrinkDemandedConstant(Instruction *I, unsigned OpNo,
return true;
}
/// ShrinkDemandedConstant - Check to see if the specified operand of the
/// specified instruction is a constant integer. If so, check to see if there
/// are any bits set in the constant that are not demanded. If so, shrink the
/// constant and return true.
static bool ShrinkDemandedConstant(Instruction *I, unsigned OpNo,
APInt Demanded) {
assert(I && "No instruction?");
assert(OpNo < I->getNumOperands() && "Operand index too large");
// If the operand is not a constant integer, nothing to do.
ConstantInt *OpC = dyn_cast<ConstantInt>(I->getOperand(OpNo));
if (!OpC) return false;
// If there are no bits set that aren't demanded, nothing to do.
Demanded.zextOrTrunc(OpC->getValue().getBitWidth());
if ((~Demanded & OpC->getValue()) == 0)
return false;
// This instruction is producing bits that are not demanded. Shrink the RHS.
Demanded &= OpC->getValue();
I->setOperand(OpNo, ConstantInt::get(Demanded));
return true;
}
// ComputeSignedMinMaxValuesFromKnownBits - Given a signed integer type and a
// set of known zero and one bits, compute the maximum and minimum values that
// could have the specified known zero and known one bits, returning them in