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https://github.com/darlinghq/darling-JavaScriptCore.git
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66 lines
3.0 KiB
C
66 lines
3.0 KiB
C
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/*
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* Copyright (C) 2015 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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#if ENABLE(DFG_JIT)
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namespace JSC { namespace DFG {
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class Graph;
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struct Node;
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// A conservative approximation of whether the node will perform the kind of effect that would prevent
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// subsequent nodes from exiting to this node's exit origin. Exiting after an effect to that effect's
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// exit origin would cause the effect to execute a second time. Two kinds of such effects can exist:
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//
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// Observable heap or stack effect: If we perform such an effect and then exit to the same origin, that
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// effect will be executed a second time, which is incorrect.
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//
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// OSR exit state update: This doesn't do any observable side-effect, but it tells OSR exit that it
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// should recover some value as if an effect had happened. For example, a MovHint will tell OSR exit
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// that some bytecode variable now has a new value. If we exit to the exit origin of a MovHint after we
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// "execute" the MovHint, then the bytecode state will look as if we had already executed that bytecode
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// instruction. This could cause issues for example for bytecode like:
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//
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// op_add r1, r1, r2
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//
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// which will get lowered to something like:
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//
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// a: ArithAdd(...)
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// b: MovHint(@a, r1)
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//
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// If we exit to the op_add after executing the MovHint, then r1 will already contain the result of the
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// add. Then after exit we'll do the add again, and r1 will have the wrong value. Because of object
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// allocation elimination and PutStack sinking, we can also have other OSR exit updates, like
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// KillStack, PutHint, among others. They don't do anything so long as we stay in optimized code, but
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// they tell OSR exit how to reconstitute state.
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bool clobbersExitState(Graph&, Node*);
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} } // namespace JSC::DFG
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#endif // ENABLE(DFG_JIT)
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