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      1 // Copyright 2013 the V8 project authors. All rights reserved.
      2 // Redistribution and use in source and binary forms, with or without
      3 // modification, are permitted provided that the following conditions are
      4 // met:
      5 //
      6 //     * Redistributions of source code must retain the above copyright
      7 //       notice, this list of conditions and the following disclaimer.
      8 //     * Redistributions in binary form must reproduce the above
      9 //       copyright notice, this list of conditions and the following
     10 //       disclaimer in the documentation and/or other materials provided
     11 //       with the distribution.
     12 //     * Neither the name of Google Inc. nor the names of its
     13 //       contributors may be used to endorse or promote products derived
     14 //       from this software without specific prior written permission.
     15 //
     16 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
     17 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
     18 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
     19 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
     20 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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     22 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     23 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
     24 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     25 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
     26 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     27 
     28 #include "hydrogen-mark-unreachable.h"
     29 
     30 namespace v8 {
     31 namespace internal {
     32 
     33 
     34 void HMarkUnreachableBlocksPhase::MarkUnreachableBlocks() {
     35   // If there is unreachable code in the graph, propagate the unreachable marks
     36   // using a fixed-point iteration.
     37   bool changed = true;
     38   const ZoneList<HBasicBlock*>* blocks = graph()->blocks();
     39   while (changed) {
     40     changed = false;
     41     for (int i = 0; i < blocks->length(); i++) {
     42       HBasicBlock* block = blocks->at(i);
     43       if (!block->IsReachable()) continue;
     44       bool is_reachable = blocks->at(0) == block;
     45       for (HPredecessorIterator it(block); !it.Done(); it.Advance()) {
     46         HBasicBlock* predecessor = it.Current();
     47         // A block is reachable if one of its predecessors is reachable,
     48         // doesn't deoptimize and either is known to transfer control to the
     49         // block or has a control flow instruction for which the next block
     50         // cannot be determined.
     51         if (predecessor->IsReachable() && !predecessor->IsDeoptimizing()) {
     52           HBasicBlock* pred_succ;
     53           bool known_pred_succ =
     54               predecessor->end()->KnownSuccessorBlock(&pred_succ);
     55           if (!known_pred_succ || pred_succ == block) {
     56             is_reachable = true;
     57             break;
     58           }
     59         }
     60         if (block->is_osr_entry()) {
     61           is_reachable = true;
     62         }
     63       }
     64       if (!is_reachable) {
     65         block->MarkUnreachable();
     66         changed = true;
     67       }
     68     }
     69   }
     70 }
     71 
     72 
     73 void HMarkUnreachableBlocksPhase::Run() {
     74   MarkUnreachableBlocks();
     75 }
     76 
     77 } }  // namespace v8::internal
     78