| // Copyright 2013 the V8 project authors. All rights reserved. |
| // Redistribution and use in source and binary forms, with or without |
| // modification, are permitted provided that the following conditions are |
| // met: |
| // |
| // * Redistributions of source code must retain the above copyright |
| // notice, this list of conditions and the following disclaimer. |
| // * Redistributions in binary form must reproduce the above |
| // copyright notice, this list of conditions and the following |
| // disclaimer in the documentation and/or other materials provided |
| // with the distribution. |
| // * Neither the name of Google Inc. nor the names of its |
| // contributors may be used to endorse or promote products derived |
| // from this software without specific prior written permission. |
| // |
| // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
| // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
| // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
| // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
| // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
| // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| |
| #ifndef V8_HYDROGEN_ALIAS_ANALYSIS_H_ |
| #define V8_HYDROGEN_ALIAS_ANALYSIS_H_ |
| |
| #include "hydrogen.h" |
| |
| namespace v8 { |
| namespace internal { |
| |
| enum HAliasing { |
| kMustAlias, |
| kMayAlias, |
| kNoAlias |
| }; |
| |
| |
| // Defines the interface to alias analysis for the rest of the compiler. |
| // A simple implementation can use only local reasoning, but a more powerful |
| // analysis might employ points-to analysis. |
| class HAliasAnalyzer : public ZoneObject { |
| public: |
| // Simple alias analysis distinguishes allocations, parameters, |
| // and constants using only local reasoning. |
| HAliasing Query(HValue* a, HValue* b) { |
| // The same SSA value always references the same object. |
| if (a == b) return kMustAlias; |
| |
| if (a->IsAllocate() || a->IsInnerAllocatedObject()) { |
| // Two non-identical allocations can never be aliases. |
| if (b->IsAllocate()) return kNoAlias; |
| if (b->IsInnerAllocatedObject()) return kNoAlias; |
| // An allocation can never alias a parameter or a constant. |
| if (b->IsParameter()) return kNoAlias; |
| if (b->IsConstant()) return kNoAlias; |
| } |
| if (b->IsAllocate() || b->IsInnerAllocatedObject()) { |
| // An allocation can never alias a parameter or a constant. |
| if (a->IsParameter()) return kNoAlias; |
| if (a->IsConstant()) return kNoAlias; |
| } |
| |
| // Constant objects can be distinguished statically. |
| if (a->IsConstant()) { |
| // TODO(titzer): DataEquals() is more efficient, but that's protected. |
| return a->Equals(b) ? kMustAlias : kNoAlias; |
| } |
| return kMayAlias; |
| } |
| |
| // Checks whether the objects referred to by the given instructions may |
| // ever be aliases. Note that this is more conservative than checking |
| // {Query(a, b) == kMayAlias}, since this method considers kMustAlias |
| // objects to also be may-aliasing. |
| inline bool MayAlias(HValue* a, HValue* b) { |
| return Query(a, b) != kNoAlias; |
| } |
| |
| inline bool MustAlias(HValue* a, HValue* b) { |
| return Query(a, b) == kMustAlias; |
| } |
| |
| inline bool NoAlias(HValue* a, HValue* b) { |
| return Query(a, b) == kNoAlias; |
| } |
| |
| // Returns the actual value of an instruction. In the case of a chain |
| // of informative definitions, return the root of the chain. |
| HValue* ActualValue(HValue* obj) { |
| while (obj->IsInformativeDefinition()) { // Walk a chain of idefs. |
| obj = obj->RedefinedOperand(); |
| } |
| return obj; |
| } |
| }; |
| |
| |
| } } // namespace v8::internal |
| |
| #endif // V8_HYDROGEN_ALIAS_ANALYSIS_H_ |