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 
7 namespace v8 {
8 namespace internal {
9 
10 
MarkUnreachableBlocks()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 
Run()50 void HMarkUnreachableBlocksPhase::Run() {
51   MarkUnreachableBlocks();
52 }
53 
54 }  // namespace internal
55 }  // namespace v8
56