mirror of
https://github.com/RPCS3/llvm-mirror.git
synced 2024-11-22 18:54:02 +01:00
ae65e281f3
to reflect the new license. We understand that people may be surprised that we're moving the header entirely to discuss the new license. We checked this carefully with the Foundation's lawyer and we believe this is the correct approach. Essentially, all code in the project is now made available by the LLVM project under our new license, so you will see that the license headers include that license only. Some of our contributors have contributed code under our old license, and accordingly, we have retained a copy of our old license notice in the top-level files in each project and repository. llvm-svn: 351636
65 lines
2.3 KiB
C++
65 lines
2.3 KiB
C++
//===-- KnownBits.cpp - Stores known zeros/ones ---------------------------===//
|
|
//
|
|
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
|
|
// See https://llvm.org/LICENSE.txt for license information.
|
|
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// 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;
|
|
}
|