| /** |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance |
| * with the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, |
| * software distributed under the License is distributed on an |
| * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| * KIND, either express or implied. See the License for the |
| * specific language governing permissions and limitations |
| * under the License. |
| */ |
| #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) |
