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-mark-unreachable.h"
6
7namespace v8 {
8namespace internal {
9
10
11void HMarkUnreachableBlocksPhase::MarkUnreachableBlocks() {
12  // If there is unreachable code in the graph, propagate the unreachable marks
13  // using a fixed-point iteration.
14  bool changed = true;
15  const ZoneList<HBasicBlock*>* blocks = graph()->blocks();
16  while (changed) {
17    changed = false;
18    for (int i = 0; i < blocks->length(); i++) {
19      HBasicBlock* block = blocks->at(i);
20      if (!block->IsReachable()) continue;
21      bool is_reachable = blocks->at(0) == block;
22      for (HPredecessorIterator it(block); !it.Done(); it.Advance()) {
23        HBasicBlock* predecessor = it.Current();
24        // A block is reachable if one of its predecessors is reachable,
25        // doesn't deoptimize and either is known to transfer control to the
26        // block or has a control flow instruction for which the next block
27        // cannot be determined.
28        if (predecessor->IsReachable() && !predecessor->IsDeoptimizing()) {
29          HBasicBlock* pred_succ;
30          bool known_pred_succ =
31              predecessor->end()->KnownSuccessorBlock(&pred_succ);
32          if (!known_pred_succ || pred_succ == block) {
33            is_reachable = true;
34            break;
35          }
36        }
37        if (block->is_osr_entry()) {
38          is_reachable = true;
39        }
40      }
41      if (!is_reachable) {
42        block->MarkUnreachable();
43        changed = true;
44      }
45    }
46  }
47}
48
49
50void HMarkUnreachableBlocksPhase::Run() {
51  MarkUnreachableBlocks();
52}
53
54} }  // namespace v8::internal
55