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/crankshaft/hydrogen-mark-unreachable.h"
6 #include "src/objects-inl.h"
7 
8 namespace v8 {
9 namespace internal {
10 
11 
MarkUnreachableBlocks()12 void HMarkUnreachableBlocksPhase::MarkUnreachableBlocks() {
13   // If there is unreachable code in the graph, propagate the unreachable marks
14   // using a fixed-point iteration.
15   bool changed = true;
16   const ZoneList<HBasicBlock*>* blocks = graph()->blocks();
17   while (changed) {
18     changed = false;
19     for (int i = 0; i < blocks->length(); i++) {
20       HBasicBlock* block = blocks->at(i);
21       if (!block->IsReachable()) continue;
22       bool is_reachable = blocks->at(0) == block;
23       for (HPredecessorIterator it(block); !it.Done(); it.Advance()) {
24         HBasicBlock* predecessor = it.Current();
25         // A block is reachable if one of its predecessors is reachable,
26         // doesn't deoptimize and either is known to transfer control to the
27         // block or has a control flow instruction for which the next block
28         // cannot be determined.
29         if (predecessor->IsReachable() && !predecessor->IsDeoptimizing()) {
30           HBasicBlock* pred_succ;
31           bool known_pred_succ =
32               predecessor->end()->KnownSuccessorBlock(&pred_succ);
33           if (!known_pred_succ || pred_succ == block) {
34             is_reachable = true;
35             break;
36           }
37         }
38         if (block->is_osr_entry()) {
39           is_reachable = true;
40         }
41       }
42       if (!is_reachable) {
43         block->MarkUnreachable();
44         changed = true;
45       }
46     }
47   }
48 }
49 
50 
Run()51 void HMarkUnreachableBlocksPhase::Run() {
52   MarkUnreachableBlocks();
53 }
54 
55 }  // namespace internal
56 }  // namespace v8
57