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