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/*
* Copyright (C) 2018 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#pragma once
#include <wtf/PrintStream.h>
namespace WTF {
// This is a boolean type that is part of an abstract value lattice. It's useful for inferring what
// the boolean value of something is by exploring all boolean values we encounter.
//
// It's useful to think of a lattice as a set. The comments below also describe what the enum values
// mean in terms of sets.
//
// FIXME: This would work a lot better as a class with methods. Then we could ensure that the default
// value is always Bottom, we could have nice conversions to and from boolean, and things like the
// leastUpperBound function could be a member function with a nicer name.
// https://bugs.webkit.org/show_bug.cgi?id=185804
enum class BooleanLattice : uint8_t {
// Bottom means that we haven't seen any boolean values yet. We don't know what boolean value we
// will infer yet. If we are left with Bottom after we have considered all booleans, it means
// that we did not see any booleans.
//
// This represents the empty set.
Bottom = 0,
// We definitely saw false.
//
// This represents a set that just contains false.
False = 1,
// We definitely saw true.
//
// This represents a set that just contains true.
True = 2,
// Top means that we have seen both false and true. Like Bottom, it means that we don't know what
// boolean value this lattice has. But unlike Bottom, which bases its lack of knowledge on not
// having seen any booleans, Top bases its lack of knowledge based on having seen both False and
// True.
//
// This represents a set that contains both false and true.
Top = 3
};
inline BooleanLattice leastUpperBoundOfBooleanLattices(BooleanLattice a, BooleanLattice b)
{
return static_cast<BooleanLattice>(static_cast<uint8_t>(a) | static_cast<uintptr_t>(b));
}
inline void printInternal(PrintStream& out, BooleanLattice value)
{
switch (value) {
case BooleanLattice::Bottom:
out.print("Bottom");
return;
case BooleanLattice::False:
out.print("False");
return;
case BooleanLattice::True:
out.print("True");
return;
case BooleanLattice::Top:
out.print("Top");
return;
}
RELEASE_ASSERT_NOT_REACHED();
}
} // namespace WTF
using WTF::BooleanLattice;
using WTF::leastUpperBoundOfBooleanLattices;
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