[PATCH] D68672: [APInt] Rounding right-shifts

[Nikita Popov via Phabricator via llvm-commits]

nikic added a comment.

In D68672#1707404 <https://reviews.llvm.org/D68672#1707404>, @lebedev.ri wrote:

> I'm not sure i can parse that, fall out?


Sorry, what I meant is that the normal lshr/ashr will behave as desired for the purposes of determining a shl GNWR range. Something along the lines of...

  case Instruction::Shl: {
    APInt UMax = Other.getUnsignedMax();
    unsigned MaxShift = Unsigned ? BitWidth - 1 : BitWidth - 2;
    if (UMax.uge(MaxShift)) // (An intersect would be more precise)
      return ConstantRange(APInt::getNullValue(BitWidth));
    if (Unsigned)
      return getNonEmpty(APInt::getNullValue(BitWidth),
                         APInt::getMaxValue(BitWidth).lshr(UMax) + 1);
    return getNonEmpty(APInt::getSignedMinValue(BitWidth).ashr(UMax)
                       APInt::getSignedMaxValue(BitWidth).ashr(UMax) + 1);
  }

We can still add these methods, they just don't seem necessary for the use-case you mentioned, unless I'm missing something.


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https://reviews.llvm.org/D68672