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