DFGClobbersExitState.cpp   [plain text]

/*
 * Copyright (C) 2015 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
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#include "config.h"
#include "DFGClobbersExitState.h"

#if ENABLE(DFG_JIT)

#include "DFGClobberize.h"
#include "DFGGraph.h"
#include "DFGNode.h"
#include "JSCInlines.h"

namespace JSC { namespace DFG {

bool clobbersExitState(Graph& graph, Node* node)
{
    // There are certain nodes whose effect on the exit state has nothing to do with what they
    // normally clobber.
    switch (node->op()) {
    case MovHint:
    case ZombieHint:
    case PutHint:
    case KillStack:
        return true;

    case SetLocal:
    case PutStack:
        // These nodes write to the stack, but they may only do so after we have already had a MovHint
        // for the exact same value and the same stack location. Hence, they have no further effect on
        // exit state.
        return false;

    case ArrayifyToStructure:
    case Arrayify:
    case NewObject:
    case NewRegexp:
    case NewStringObject:
    case PhantomNewObject:
    case MaterializeNewObject:
    case PhantomNewFunction:
    case PhantomNewGeneratorFunction:
    case PhantomCreateActivation:
    case MaterializeCreateActivation:
    case CountExecution:
    case AllocatePropertyStorage:
    case ReallocatePropertyStorage:
        // These do clobber memory, but nothing that is observable. It may be nice to separate the
        // heaps into those that are observable and those that aren't, but we don't do that right now.
        // FIXME: https://bugs.webkit.org/show_bug.cgi?id=148440
        return false;

    case CreateActivation:
        // Like above, but with the activation allocation caveat.
        return node->castOperand<SymbolTable*>()->singletonScope()->isStillValid();

    case NewFunction:
    case NewGeneratorFunction:
        // Like above, but with the JSFunction allocation caveat.
        return node->castOperand<FunctionExecutable*>()->singletonFunction()->isStillValid();

    default:
        // For all other nodes, we just care about whether they write to something other than SideState.
        bool result = false;
        clobberize(
            graph, node, NoOpClobberize(),
            [&] (const AbstractHeap& heap) {
                // There shouldn't be such a thing as a strict subtype of SideState. That's what allows
                // us to use a fast != check, below.
                ASSERT(!heap.isStrictSubtypeOf(SideState));

                if (heap != SideState)
                    result = true;
            },
            NoOpClobberize());
        return result;
    }
}

} } // namespace JSC::DFG

#endif // ENABLE(DFG_JIT)