graph-trimmer.cc

// Copyright 2015 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.

#include "src/compiler/graph-trimmer.h"

#include "src/compiler/graph.h"

namespace v8 {
namespace internal {
namespace compiler {

GraphTrimmer::GraphTrimmer(Zone* zone, Graph* graph)
    : graph_(graph), is_live_(graph, 2), live_(zone) {
  live_.reserve(graph->NodeCount());
}


GraphTrimmer::~GraphTrimmer() = default;


void GraphTrimmer::TrimGraph() {
  // Mark end node as live.
  MarkAsLive(graph()->end());
  // Compute transitive closure of live nodes.
  for (size_t i = 0; i < live_.size(); ++i) {
    Node* const live = live_[i];
    for (Node* const input : live->inputs()) MarkAsLive(input);
  }
  // Remove dead->live edges.
  for (Node* const live : live_) {
    DCHECK(IsLive(live));
    for (Edge edge : live->use_edges()) {
      Node* const user = edge.from();
      if (!IsLive(user)) {
        if (FLAG_trace_turbo_trimming) {
          StdoutStream{} << "DeadLink: " << *user << "(" << edge.index()
                         << ") -> " << *live << std::endl;
        }
        edge.UpdateTo(nullptr);
      }
    }
  }
}

}  // namespace compiler
}  // namespace internal
}  // namespace v8