| /* |
| * Copyright (C) 2016 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. AND ITS CONTRIBUTORS ``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 ITS 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; |
| |
| // Picks up groups of barriers that could be executed in any order with respect to each other and |
| // places then at the earliest point in the program where the cluster would be correct. This phase |
| // makes only the first of the cluster be a FencedStoreBarrier while the rest are normal |
| // StoreBarriers. This phase also removes redundant barriers - for example, the cluster may end up |
| // with two or more barriers on the same object, in which case it is totally safe for us to drop |
| // one of them. The reason why this is sound hinges on the "earliest point where the cluster would |
| // be correct" property. For example, take this input: |
| // |
| // a: Call() |
| // b: PutByOffset(@o, @o, @x) |
| // c: FencedStoreBarrier(@o) |
| // d: PutByOffset(@o, @o, @y) |
| // e: FencedStoreBarrier(@o) |
| // f: PutByOffset(@p, @p, @z) |
| // g: FencedStoreBarrier(@p) |
| // h: GetByOffset(@q) |
| // i: Call() |
| // |
| // The cluster of barriers is @c, @e, and @g. All of the barriers are between two doesGC effects: |
| // the calls at @a and @i. Because there are no doesGC effects between @a and @i and there is no |
| // possible control flow entry into this sequence between @ and @i, we could could just execute all |
| // of the barriers just before @i in any order. The earliest point where the cluster would be |
| // correct is just after @f, since that's the last operation that needs a barrier. We use the |
| // earliest to reduce register pressure. When the barriers are clustered just after @f, we get: |
| // |
| // a: Call() |
| // b: PutByOffset(@o, @o, @x) |
| // d: PutByOffset(@o, @o, @y) |
| // f: PutByOffset(@p, @p, @z) |
| // c: FencedStoreBarrier(@o) |
| // e: FencedStoreBarrier(@o) |
| // g: FencedStoreBarrier(@p) |
| // h: GetByOffset(@q) |
| // i: Call() |
| // |
| // This phase does more. It takes advantage of the clustering to remove fences and remove redundant |
| // barriers. So this phase will output this: |
| // |
| // a: Call() |
| // b: PutByOffset(@o, @o, @x) |
| // d: PutByOffset(@o, @o, @y) |
| // f: PutByOffset(@p, @p, @z) |
| // c: FencedStoreBarrier(@o) |
| // g: StoreBarrier(@p) |
| // h: GetByOffset(@q) |
| // i: Call() |
| // |
| // This optimization improves both overall throughput and the throughput while the concurrent GC is |
| // running. In the former, we are simplifying instruction selection for all but the first fence. In |
| // the latter, we are reducing the cost of all but the first barrier. The first barrier will awlays |
| // take slow path when there is concurrent GC activity, since the slow path contains the fence. But |
| // all of the other barriers will only take slow path if they really need to remember the object. |
| bool performStoreBarrierClustering(Graph&); |
| |
| } } // namespace JSC::DFG |
| |
| #endif // ENABLE(DFG_JIT) |
| |
