// Copyright 2016 the V8 project authors. All rights reserved. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. #ifndef V8_COMPILER_STORE_STORE_ELIMINATION_H_ #define V8_COMPILER_STORE_STORE_ELIMINATION_H_ #include "src/common/globals.h" namespace v8 { namespace internal { class TickCounter; class Zone; namespace compiler { class JSGraph; // Store-store elimination. // // The aim of this optimization is to detect the following pattern in the // effect graph: // // - StoreField[+24, kRepTagged](263, ...) // // ... lots of nodes from which the field at offset 24 of the object // returned by node #263 cannot be observed ... // // - StoreField[+24, kRepTagged](263, ...) // // In such situations, the earlier StoreField cannot be observed, and can be // eliminated. This optimization should work for any offset and input node, of // course. // // The optimization also works across splits. It currently does not work for // loops, because we tend to put a stack check in loops, and like deopts, // stack checks can observe anything. // Assumption: every byte of a JS object is only ever accessed through one // offset. For instance, byte 15 of a given object may be accessed using a // two-byte read at offset 14, or a four-byte read at offset 12, but never // both in the same program. // // This implementation needs all dead nodes removed from the graph, and the // graph should be trimmed. class StoreStoreElimination final : public AllStatic { public: static void Run(JSGraph* js_graph, TickCounter* tick_counter, Zone* temp_zone); }; } // namespace compiler } // namespace internal } // namespace v8 #endif // V8_COMPILER_STORE_STORE_ELIMINATION_H_