1// Copyright 2013 the V8 project authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#include "src/hydrogen-sce.h"
6#include "src/v8.h"
7
8namespace v8 {
9namespace internal {
10
11void HStackCheckEliminationPhase::Run() {
12  // For each loop block walk the dominator tree from the backwards branch to
13  // the loop header. If a call instruction is encountered the backwards branch
14  // is dominated by a call and the stack check in the backwards branch can be
15  // removed.
16  for (int i = 0; i < graph()->blocks()->length(); i++) {
17    HBasicBlock* block = graph()->blocks()->at(i);
18    if (block->IsLoopHeader()) {
19      HBasicBlock* back_edge = block->loop_information()->GetLastBackEdge();
20      HBasicBlock* dominator = back_edge;
21      while (true) {
22        for (HInstructionIterator it(dominator); !it.Done(); it.Advance()) {
23          if (it.Current()->HasStackCheck()) {
24            block->loop_information()->stack_check()->Eliminate();
25            break;
26          }
27        }
28
29        // Done when the loop header is processed.
30        if (dominator == block) break;
31
32        // Move up the dominator tree.
33        dominator = dominator->dominator();
34      }
35    }
36  }
37}
38
39} }  // namespace v8::internal
40