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-removable-simulates.h" 29 30 namespace v8 { 31 namespace internal { 32 33 void HMergeRemovableSimulatesPhase::Run() { 34 ZoneList<HSimulate*> mergelist(2, zone()); 35 for (int i = 0; i < graph()->blocks()->length(); ++i) { 36 HBasicBlock* block = graph()->blocks()->at(i); 37 // Make sure the merge list is empty at the start of a block. 38 ASSERT(mergelist.is_empty()); 39 // Nasty heuristic: Never remove the first simulate in a block. This 40 // just so happens to have a beneficial effect on register allocation. 41 bool first = true; 42 for (HInstructionIterator it(block); !it.Done(); it.Advance()) { 43 HInstruction* current = it.Current(); 44 if (current->IsLeaveInlined()) { 45 // Never fold simulates from inlined environments into simulates 46 // in the outer environment. 47 // (Before each HEnterInlined, there is a non-foldable HSimulate 48 // anyway, so we get the barrier in the other direction for free.) 49 // Simply remove all accumulated simulates without merging. This 50 // is safe because simulates after instructions with side effects 51 // are never added to the merge list. 52 while (!mergelist.is_empty()) { 53 mergelist.RemoveLast()->DeleteAndReplaceWith(NULL); 54 } 55 continue; 56 } 57 if (current->IsReturn()) { 58 // Drop mergeable simulates in the list. This is safe because 59 // simulates after instructions with side effects are never added 60 // to the merge list. 61 while (!mergelist.is_empty()) { 62 mergelist.RemoveLast()->DeleteAndReplaceWith(NULL); 63 } 64 continue; 65 } 66 // Skip the non-simulates and the first simulate. 67 if (!current->IsSimulate()) continue; 68 if (first) { 69 first = false; 70 continue; 71 } 72 HSimulate* current_simulate = HSimulate::cast(current); 73 if ((current_simulate->previous()->HasObservableSideEffects() && 74 !current_simulate->next()->IsSimulate()) || 75 !current_simulate->is_candidate_for_removal()) { 76 // This simulate is not suitable for folding. 77 // Fold the ones accumulated so far. 78 current_simulate->MergeWith(&mergelist); 79 continue; 80 } else { 81 // Accumulate this simulate for folding later on. 82 mergelist.Add(current_simulate, zone()); 83 } 84 } 85 86 if (!mergelist.is_empty()) { 87 // Merge the accumulated simulates at the end of the block. 88 HSimulate* last = mergelist.RemoveLast(); 89 last->MergeWith(&mergelist); 90 } 91 } 92 } 93 94 } } // namespace v8::internal 95
