src/passes/Untee.cpp

/*
 * 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.
 */

//
// Removes local.tees, replacing them with gets and sets.
//
// This makes the code "flatter", with less nested side
// effects. That can make some passes, like CodePushing,
// more effective.
//

#include <pass.h>
#include <wasm-builder.h>
#include <wasm.h>

namespace wasm {

struct Untee : public WalkerPass<PostWalker<Untee>> {
  bool isFunctionParallel() override { return true; }

  std::unique_ptr<Pass> create() override { return std::make_unique<Untee>(); }

  void visitLocalSet(LocalSet* curr) {
    if (curr->isTee()) {
      if (curr->value->type == Type::unreachable) {
        // we don't reach the tee, just remove it
        replaceCurrent(curr->value);
      } else {
        // a normal tee. replace with set and get
        Builder builder(*getModule());
        LocalGet* get = builder.makeLocalGet(
          curr->index, getFunction()->getLocalType(curr->index));
        replaceCurrent(builder.makeSequence(curr, get));
        curr->makeSet();
      }
    }
  }
};

Pass* createUnteePass() { return new Untee(); }

} // namespace wasm