================ @@ -1735,6 +1746,122 @@ ConstantRange ConstantRange::ctlz(bool ZeroIsPoison) const { return getNonEmpty(APInt(getBitWidth(), getUnsignedMax().countl_zero()), APInt(getBitWidth(), getUnsignedMin().countl_zero() + 1)); } +static ConstantRange getUnsignedCountTrailingZerosRange(const APInt &Lower, + const APInt &Upper) { + assert(Lower.ule(Upper)); + unsigned BitWidth = Lower.getBitWidth(); + if (Lower == Upper) + return ConstantRange::getEmpty(BitWidth); + if (Lower + 1 == Upper) + return ConstantRange(APInt(BitWidth, Lower.countr_zero())); + if (Lower.isZero()) + return ConstantRange(APInt::getZero(BitWidth), + APInt(BitWidth, BitWidth + 1)); + + // Calculate longest common prefix. + unsigned LCPLength = (Lower ^ (Upper - 1)).countl_zero(); + // If Lower is {LCP, 000...}, the maximum is Lower.countr_zero(). + // Otherwise, the maximum is BitWidth - LCPLength - 1 ({LCP, 100...}). + return ConstantRange( + APInt::getZero(BitWidth), + APInt(BitWidth, std::max(BitWidth - LCPLength, Lower.countr_zero() + 1))); +} + +ConstantRange ConstantRange::cttz(bool ZeroIsPoison) const { + if (isEmptySet()) + return getEmpty(); + + APInt Zero = APInt::getZero(getBitWidth()); + + if (ZeroIsPoison && contains(Zero)) { + // ZeroIsPoison is set, and zero is contained. We discern three cases, in + // which a zero can appear: + // 1) Lower is zero, handling cases of kind [0, 1), [0, 2), etc. + // 2) Upper is zero, wrapped set, handling cases of kind [3, 0], etc. + // 3) Zero contained in a wrapped set, e.g., [3, 2), [3, 1), etc. + + if (getLower().isZero()) { + if ((getUpper() - 1).isZero()) { + // We have in input interval of kind [0, 1). In this case we cannot + // really help but return empty-set. + return getEmpty(); + } + + // Compute the resulting range by excluding zero from Lower. + return getUnsignedCountTrailingZerosRange(getLower() + 1, getUpper()); + } else if ((getUpper() - 1).isZero()) { + // Compute the resulting range by excluding zero from Upper. + return ConstantRange( + Zero, APInt(getBitWidth(), + (getUnsignedMax() - getLower() + 1).logBase2() + 1)); ---------------- dtcxzyw wrote:
It calculates the range of `cttz` for the input range `[Lower, UnsignedMax]`. See also https://godbolt.org/z/jMhcs5375 https://github.com/llvm/llvm-project/pull/67917 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits