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[ValueTracking] Remove deadish code from computeKnownBitsAddSub.

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The code assigned to KnownZero, but later code unconditionally assigned over it. I'm pretty sure the later code can handle the same cases and more equally well.

llvm-svn: 298190
This commit is contained in:
Craig Topper 2017-03-18 18:21:46 +00:00
parent 1230ec8164
commit 0a85a90476
1 changed files with 0 additions and 24 deletions
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24
lib/Analysis/ValueTracking.cpp
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@ -255,30 +255,6 @@ static void computeKnownBitsAddSub(bool Add, const Value *Op0, const Value *Op1,
APInt &KnownZero, APInt &KnownOne,
APInt &KnownZero2, APInt &KnownOne2,
unsigned Depth, const Query &Q) {
if (!Add) {
if (const ConstantInt *CLHS = dyn_cast<ConstantInt>(Op0)) {
// We know that the top bits of C-X are clear if X contains less bits
// than C (i.e. no wrap-around can happen). For example, 20-X is
// positive if we can prove that X is >= 0 and < 16.
if (!CLHS->getValue().isNegative()) {
unsigned BitWidth = KnownZero.getBitWidth();
unsigned NLZ = (CLHS->getValue()+1).countLeadingZeros();
// NLZ can't be BitWidth with no sign bit
APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1);
computeKnownBits(Op1, KnownZero2, KnownOne2, Depth + 1, Q);
// If all of the MaskV bits are known to be zero, then we know the
// output top bits are zero, because we now know that the output is
// from [0-C].
if ((KnownZero2 & MaskV) == MaskV) {
unsigned NLZ2 = CLHS->getValue().countLeadingZeros();
// Top bits known zero.
KnownZero = APInt::getHighBitsSet(BitWidth, NLZ2);
}
}
}
}
unsigned BitWidth = KnownZero.getBitWidth();
// If an initial sequence of bits in the result is not needed, the