src/ir/properties.cpp

/*
 * Copyright 2021 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.
 */

#include "ir/properties.h"
#include "wasm-traversal.h"

namespace wasm::Properties {

bool isGenerative(Expression* curr, FeatureSet features) {
  // Practically no wasm instructions are generative. Exceptions occur only in
  // GC atm.
  if (!features.hasGC()) {
    return false;
  }

  struct Scanner : public PostWalker<Scanner> {
    bool generative = false;
    void visitStructNew(StructNew* curr) { generative = true; }
    void visitArrayNew(ArrayNew* curr) { generative = true; }
    void visitArrayInit(ArrayInit* curr) { generative = true; }
  } scanner;
  scanner.walk(curr);
  return scanner.generative;
}

Expression* getSingleDescendantWithEffects(Expression* curr, const PassOptions& options, Module& module) {
  struct Scanner : public PostWalker<Scanner, UnifiedExpressionVisitor<Scanner>> {
    const PassOptions& options;
    Module& module;

    Scanner(const PassOptions& options, Module& module) : options(options), module(module) {}

    Expression* withEffects = nullptr;
    bool multiple = false;

    void visitExpression(Expression* curr) {
      if (multiple) {
        return;
      }
      // This handles simple patterns, but cannot ignore nested things that can
      // be ignored as a whole, which the SimplifyGlobals readOnlyToWrite code
      // might be able to.
      ShallowEffectAnalyzer effects(options, module, curr);
      if (effects.hasSideEffects() || effects.readsMutableGlobalState()) {
        if (withEffects) {
          multiple = true;
          withEffects = nullptr;
        } else {
          withEffects = curr;
        }
      }
    }
  } scanner(options, module);
  scanner.walk(curr);
  return scanner.withEffects;
}

} // namespace wasm::Properties