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 #ifndef V8_HYDROGEN_ALIAS_ANALYSIS_H_ 29 #define V8_HYDROGEN_ALIAS_ANALYSIS_H_ 30 31 #include "hydrogen.h" 32 33 namespace v8 { 34 namespace internal { 35 36 enum HAliasing { 37 kMustAlias, 38 kMayAlias, 39 kNoAlias 40 }; 41 42 43 // Defines the interface to alias analysis for the rest of the compiler. 44 // A simple implementation can use only local reasoning, but a more powerful 45 // analysis might employ points-to analysis. 46 class HAliasAnalyzer : public ZoneObject { 47 public: 48 // Simple alias analysis distinguishes allocations, parameters, 49 // and constants using only local reasoning. 50 HAliasing Query(HValue* a, HValue* b) { 51 // The same SSA value always references the same object. 52 if (a == b) return kMustAlias; 53 54 if (a->IsAllocate() || a->IsInnerAllocatedObject()) { 55 // Two non-identical allocations can never be aliases. 56 if (b->IsAllocate()) return kNoAlias; 57 if (b->IsInnerAllocatedObject()) return kNoAlias; 58 // An allocation can never alias a parameter or a constant. 59 if (b->IsParameter()) return kNoAlias; 60 if (b->IsConstant()) return kNoAlias; 61 } 62 if (b->IsAllocate() || b->IsInnerAllocatedObject()) { 63 // An allocation can never alias a parameter or a constant. 64 if (a->IsParameter()) return kNoAlias; 65 if (a->IsConstant()) return kNoAlias; 66 } 67 68 // Constant objects can be distinguished statically. 69 if (a->IsConstant()) { 70 // TODO(titzer): DataEquals() is more efficient, but that's protected. 71 return a->Equals(b) ? kMustAlias : kNoAlias; 72 } 73 return kMayAlias; 74 } 75 76 // Checks whether the objects referred to by the given instructions may 77 // ever be aliases. Note that this is more conservative than checking 78 // {Query(a, b) == kMayAlias}, since this method considers kMustAlias 79 // objects to also be may-aliasing. 80 inline bool MayAlias(HValue* a, HValue* b) { 81 return Query(a, b) != kNoAlias; 82 } 83 84 inline bool MustAlias(HValue* a, HValue* b) { 85 return Query(a, b) == kMustAlias; 86 } 87 88 inline bool NoAlias(HValue* a, HValue* b) { 89 return Query(a, b) == kNoAlias; 90 } 91 }; 92 93 94 } } // namespace v8::internal 95 96 #endif // V8_HYDROGEN_ALIAS_ANALYSIS_H_ 97
