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[SystemZ] Address review comments for r233689

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Change lowerCTPOP to:
- Gracefully handle a known-zero input value
- Simplify computation of significant bit size

Thanks to Jay Foad for the review!



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233736 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Ulrich Weigand 2015-03-31 19:28:50 +00:00
parent 1b10376319
commit a9204bb532
1 changed files with 5 additions and 4 deletions
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9
lib/Target/SystemZ/SystemZISelLowering.cpp
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@ -2319,12 +2319,13 @@ SDValue SystemZTargetLowering::lowerCTPOP(SDValue Op,
Op = Op.getOperand(0);
APInt KnownZero, KnownOne;
DAG.computeKnownBits(Op, KnownZero, KnownOne);
uint64_t Mask = ~KnownZero.getZExtValue();
unsigned NumSignificantBits = (~KnownZero).getActiveBits();
if (NumSignificantBits == 0)
return DAG.getConstant(0, VT);
// Skip known-zero high parts of the operand.
int64_t BitSize = OrigBitSize;
while ((Mask & ((((uint64_t)1 << (BitSize / 2)) - 1) << (BitSize / 2))) == 0)
BitSize = BitSize / 2;
int64_t BitSize = (int64_t)1 << Log2_32_Ceil(NumSignificantBits);
BitSize = std::min(BitSize, OrigBitSize);
// The POPCNT instruction counts the number of bits in each byte.
Op = DAG.getNode(ISD::ANY_EXTEND, DL, MVT::i64, Op);