src/hydrogen-sce.cc

// Copyright 2013 the V8 project authors. All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
//       notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
//       copyright notice, this list of conditions and the following
//       disclaimer in the documentation and/or other materials provided
//       with the distribution.
//     * Neither the name of Google Inc. nor the names of its
//       contributors may be used to endorse or promote products derived
//       from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#include "hydrogen-sce.h"
#include "v8.h"

namespace v8 {
namespace internal {

void HStackCheckEliminationPhase::Run() {
  // For each loop block walk the dominator tree from the backwards branch to
  // the loop header. If a call instruction is encountered the backwards branch
  // is dominated by a call and the stack check in the backwards branch can be
  // removed.
  for (int i = 0; i < graph()->blocks()->length(); i++) {
    HBasicBlock* block = graph()->blocks()->at(i);
    if (block->IsLoopHeader()) {
      HBasicBlock* back_edge = block->loop_information()->GetLastBackEdge();
      HBasicBlock* dominator = back_edge;
      while (true) {
        for (HInstructionIterator it(dominator); !it.Done(); it.Advance()) {
          if (it.Current()->IsCall()) {
            block->loop_information()->stack_check()->Eliminate();
            break;
          }
        }

        // Done when the loop header is processed.
        if (dominator == block) break;

        // Move up the dominator tree.
        dominator = dominator->dominator();
      }
    }
  }
}

} }  // namespace v8::internal