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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 | |
7 namespace v8 { | |
8 namespace internal { | |
9 | |
10 | |
11 void 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 | |
50 void HMarkUnreachableBlocksPhase::Run() { | |
51 MarkUnreachableBlocks(); | |
52 } | |
53 | |
54 } // namespace internal | |
55 } // namespace v8 | |
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