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simplify/clarify control flow and improve comments, no functionality change.

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llvm-svn: 63480
This commit is contained in:
Chris Lattner 2009-01-31 08:24:16 +00:00
parent a899f8b75d
commit 85ecfee7f3
1 changed files with 21 additions and 13 deletions
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34
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -817,22 +817,30 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
if (isa<UndefValue>(V))
return 0;
return UndefValue::get(VTy);
} else if (!V->hasOneUse()) { // Other users may use these bits.
if (Depth != 0) { // Not at the root.
// Just compute the KnownZero/KnownOne bits to simplify things downstream.
ComputeMaskedBits(V, DemandedMask, KnownZero, KnownOne, Depth);
return 0;
}
// If this is the root being simplified, allow it to have multiple uses,
// just set the DemandedMask to all bits.
DemandedMask = APInt::getAllOnesValue(BitWidth);
} else if (Depth == 6) { // Limit search depth.
return 0;
}
if (Depth == 6) // Limit search depth.
return 0;
Instruction *I = dyn_cast<Instruction>(V);
if (!I) return 0; // Only analyze instructions.
// If there are multiple uses of this value and we aren't at the root, then
// we can't do any simplifications of the operands, because DemandedMask
// only reflects the bits demanded by *one* of the users.
if (Depth != 0 && !I->hasOneUse()) {
// Compute the KnownZero/KnownOne bits to simplify things downstream.
ComputeMaskedBits(I, DemandedMask, KnownZero, KnownOne, Depth);
return 0;
}
// If this is the root being simplified, allow it to have multiple uses,
// just set the DemandedMask to all bits so that we can try to simplify the
// operands. This allows visitTruncInst (for example) to simplify the
// operand of a trunc without duplicating all the logic below.
if (Depth == 0 && !V->hasOneUse())
DemandedMask = APInt::getAllOnesValue(BitWidth);
APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
APInt &RHSKnownZero = KnownZero, &RHSKnownOne = KnownOne;
switch (I->getOpcode()) {
@ -6960,7 +6968,7 @@ Instruction *InstCombiner::commonShiftTransforms(BinaryOperator &I) {
Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantInt *Op1,
BinaryOperator &I) {
bool isLeftShift = I.getOpcode() == Instruction::Shl;
bool isLeftShift = I.getOpcode() == Instruction::Shl;
// See if we can simplify any instructions used by the instruction whose sole
// purpose is to compute bits we don't care about.