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, 21 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 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