[llvm] [ConstantRange] Improve `shlWithNoWrap` (PR #101800)
Nikita Popov via llvm-commits
llvm-commits at lists.llvm.org
Sat Aug 3 09:43:34 PDT 2024
================
@@ -1624,12 +1624,43 @@ ConstantRange ConstantRange::shlWithNoWrap(const ConstantRange &Other,
return getEmpty();
ConstantRange Result = shl(Other);
+ if (!NoWrapKind)
+ return Result;
- if (NoWrapKind & OverflowingBinaryOperator::NoSignedWrap)
- Result = Result.intersectWith(sshl_sat(Other), RangeType);
+ KnownBits Known = toKnownBits();
+
+ if (NoWrapKind & OverflowingBinaryOperator::NoSignedWrap) {
+ ConstantRange ShAmtRange = Other;
+ if (isAllNonNegative())
+ ShAmtRange = ShAmtRange.intersectWith(
+ ConstantRange(APInt::getZero(getBitWidth()),
+ APInt(getBitWidth(), Known.countMaxLeadingZeros())),
+ Unsigned);
+ else if (isAllNegative())
+ ShAmtRange = ShAmtRange.intersectWith(
+ ConstantRange(APInt::getZero(getBitWidth()),
+ APInt(getBitWidth(), Known.countMaxLeadingOnes())),
+ Unsigned);
+ Result = Result.intersectWith(sshl_sat(ShAmtRange), RangeType);
+ }
- if (NoWrapKind & OverflowingBinaryOperator::NoUnsignedWrap)
- Result = Result.intersectWith(ushl_sat(Other), RangeType);
+ if (NoWrapKind & OverflowingBinaryOperator::NoUnsignedWrap) {
+ bool Overflow;
+ APInt LHSMin = getUnsignedMin();
+ APInt MinShl = LHSMin.ushl_ov(Other.getUnsignedMin(), Overflow);
+ if (Overflow)
+ return getEmpty();
+ APInt LHSMax = getUnsignedMax();
+ APInt MaxShl = LHSMax << Other.getUnsignedMax().getLimitedValue(
+ LHSMax.countLeadingZeros());
----------------
nikic wrote:
We should also take the minimum shift amount into account. E.g. this case can be skipped if MinShAmt <= LeadingZeros. So for example Full << [1,..] should give [0, -1) not Full. And the case below can be similarly adjusted.
https://github.com/llvm/llvm-project/pull/101800
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