src/ir/local-graph.h

/*
 * Copyright 2017 WebAssembly Community Group participants
 *
 * Licensed 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.
 */

#ifndef wasm_ir_local_graph_h
#define wasm_ir_local_graph_h

namespace wasm {

//
// Finds the connections between get_locals and set_locals, creating
// a graph of those ties. This is useful for "ssa-style" optimization,
// in which you want to know exactly which sets are relevant for a
// a get, so it is as if each get has just one set, logically speaking
// (see the SSA pass for actually creating new local indexes based
// on this).
//
struct LocalGraph {
  // main API

  // the constructor computes getSetses, the sets affecting each get
  LocalGraph(Function* func);

  // the set_locals relevant for an index or a get.
  typedef std::set<SetLocal*> Sets;

  typedef std::map<GetLocal*, Sets> GetSetses;

  typedef std::map<Expression*, Expression**> Locations;

  // externally useful information
  GetSetses getSetses; // the sets affecting each get. a nullptr set means the initial
                       // value (0 for a var, the received value for a param)
  Locations locations; // where each get and set is (for easy replacing)

  // optional computation: compute the influence graphs between sets and gets
  // (useful for algorithms that propagate changes)

  std::unordered_map<GetLocal*, std::unordered_set<SetLocal*>> getInfluences; // for each get, the sets whose values are influenced by that get
  std::unordered_map<SetLocal*, std::unordered_set<GetLocal*>> setInfluences; // for each set, the gets whose values are influenced by that set

  void computeInfluences();
};

} // namespace wasm

#endif // wasm_ir_local_graph_h