llvm-mirror/include/llvm/Support/KnownBits.h

//===- llvm/Support/KnownBits.h - Stores known zeros/ones -------*- C++ -*-===//
//
//                     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.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_SUPPORT_KNOWNBITS_H
#define LLVM_SUPPORT_KNOWNBITS_H

#include "llvm/ADT/APInt.h"

namespace llvm {

// Struct for tracking the known zeros and ones of a value.
struct KnownBits {
  APInt Zero;
  APInt One;

  // Default construct Zero and One.
  KnownBits() {}

  /// Create a known bits object of BitWidth bits initialized to unknown.
  KnownBits(unsigned BitWidth) : Zero(BitWidth, 0), One(BitWidth, 0) {}

  /// Get the bit width of this value.
  unsigned getBitWidth() const {
    assert(Zero.getBitWidth() == One.getBitWidth() &&
           "Zero and One should have the same width!");
    return Zero.getBitWidth();
  }

  /// Returns true if this value is known to be negative.
  bool isNegative() const { return One.isSignBitSet(); }

  /// Returns true if this value is known to be non-negative.
  bool isNonNegative() const { return Zero.isSignBitSet(); }

  /// Make this value negative.
  void makeNegative() {
    assert(!isNonNegative() && "Can't make a non-negative value negative");
    One.setSignBit();
  }

  /// Make this value negative.
  void makeNonNegative() {
    assert(!isNegative() && "Can't make a negative value non-negative");
    Zero.setSignBit();
  }
};

} // end namespace llvm

#endif