//===-- KnownBits.cpp - Stores known zeros/ones ---------------------------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This file contains a class for representing known zeros and ones used by // computeKnownBits. // //===----------------------------------------------------------------------===// #include "llvm/Support/KnownBits.h" using namespace llvm; KnownBits KnownBits::computeForAddSub(bool Add, bool NSW, const KnownBits &LHS, KnownBits RHS) { // Carry in a 1 for a subtract, rather than 0. bool CarryIn = false; if (!Add) { // Sum = LHS + ~RHS + 1 std::swap(RHS.Zero, RHS.One); CarryIn = true; } APInt PossibleSumZero = ~LHS.Zero + ~RHS.Zero + CarryIn; APInt PossibleSumOne = LHS.One + RHS.One + CarryIn; // Compute known bits of the carry. APInt CarryKnownZero = ~(PossibleSumZero ^ LHS.Zero ^ RHS.Zero); APInt CarryKnownOne = PossibleSumOne ^ LHS.One ^ RHS.One; // Compute set of known bits (where all three relevant bits are known). APInt LHSKnownUnion = LHS.Zero | LHS.One; APInt RHSKnownUnion = RHS.Zero | RHS.One; APInt CarryKnownUnion = std::move(CarryKnownZero) | CarryKnownOne; APInt Known = std::move(LHSKnownUnion) & RHSKnownUnion & CarryKnownUnion; assert((PossibleSumZero & Known) == (PossibleSumOne & Known) && "known bits of sum differ"); // Compute known bits of the result. KnownBits KnownOut; KnownOut.Zero = ~std::move(PossibleSumZero) & Known; KnownOut.One = std::move(PossibleSumOne) & Known; // Are we still trying to solve for the sign bit? if (!Known.isSignBitSet()) { if (NSW) { // Adding two non-negative numbers, or subtracting a negative number from // a non-negative one, can't wrap into negative. if (LHS.isNonNegative() && RHS.isNonNegative()) KnownOut.makeNonNegative(); // Adding two negative numbers, or subtracting a non-negative number from // a negative one, can't wrap into non-negative. else if (LHS.isNegative() && RHS.isNegative()) KnownOut.makeNegative(); } } return KnownOut; } |