src/ir/block-utils.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_block_h
#define wasm_ir_block_h

#include "ir/branch-utils.h"
#include "ir/effects.h"
#include "ir/manipulation.h"
#include "literal.h"
#include "wasm-builder.h"
#include "wasm.h"

namespace wasm::BlockUtils {

// if a block has just one element, it can often be replaced
// with that content
template<typename T>
inline Expression*
simplifyToContents(Block* block, T* parent, bool allowTypeChange = false) {
  auto& list = block->list;
  if (list.size() == 1 &&
      !BranchUtils::BranchSeeker::has(list[0], block->name)) {
    // just one element. try to replace the block
    auto* singleton = list[0];
    auto sideEffects =
      EffectAnalyzer(parent->getPassOptions(), *parent->getModule(), singleton)
        .hasSideEffects();
    if (!sideEffects && !singleton->type.isConcrete()) {
      // no side effects, and singleton is not returning a value, so we can
      // throw away the block and its contents, basically
      return Builder(*parent->getModule()).replaceWithIdenticalType(block);
    } else if (Type::isSubType(singleton->type, block->type) ||
               allowTypeChange) {
      return singleton;
    } else {
      // (side effects +) type change, must be block with declared value but
      // inside is unreachable (if both concrete, must match, and since no name
      // on block, we can't be branched to, so if singleton is unreachable, so
      // is the block)
      assert(block->type.isConcrete() && singleton->type == Type::unreachable);
      // we could replace with unreachable, but would need to update all
      // the parent's types
    }
  } else if (list.size() == 0) {
    ExpressionManipulator::nop(block);
  }
  return block;
}

// similar, but when we allow the type to change while doing so
template<typename T>
inline Expression* simplifyToContentsWithPossibleTypeChange(Block* block,
                                                            T* parent) {
  return simplifyToContents(block, parent, true);
}
} // namespace wasm::BlockUtils

#endif // wasm_ir_block_h