forked from OSchip/llvm-project
66 lines
2.3 KiB
C++
66 lines
2.3 KiB
C++
//===-- 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;
|
|
}
|