Ben Murdoch | b8a8cc1 | 2014-11-26 15:28:44 +0000 | [diff] [blame] | 1 | // Copyright 2013 the V8 project authors. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style license that can be |
| 3 | // found in the LICENSE file. |
| 4 | |
| 5 | #ifndef V8_HYDROGEN_ALIAS_ANALYSIS_H_ |
| 6 | #define V8_HYDROGEN_ALIAS_ANALYSIS_H_ |
| 7 | |
| 8 | #include "src/hydrogen.h" |
| 9 | |
| 10 | namespace v8 { |
| 11 | namespace internal { |
| 12 | |
| 13 | enum HAliasing { |
| 14 | kMustAlias, |
| 15 | kMayAlias, |
| 16 | kNoAlias |
| 17 | }; |
| 18 | |
| 19 | |
| 20 | // Defines the interface to alias analysis for the rest of the compiler. |
| 21 | // A simple implementation can use only local reasoning, but a more powerful |
| 22 | // analysis might employ points-to analysis. |
| 23 | class HAliasAnalyzer : public ZoneObject { |
| 24 | public: |
| 25 | // Simple alias analysis distinguishes allocations, parameters, |
| 26 | // and constants using only local reasoning. |
| 27 | HAliasing Query(HValue* a, HValue* b) { |
| 28 | // The same SSA value always references the same object. |
| 29 | if (a == b) return kMustAlias; |
| 30 | |
| 31 | if (a->IsAllocate() || a->IsInnerAllocatedObject()) { |
| 32 | // Two non-identical allocations can never be aliases. |
| 33 | if (b->IsAllocate()) return kNoAlias; |
| 34 | if (b->IsInnerAllocatedObject()) return kNoAlias; |
| 35 | // An allocation can never alias a parameter or a constant. |
| 36 | if (b->IsParameter()) return kNoAlias; |
| 37 | if (b->IsConstant()) return kNoAlias; |
| 38 | } |
| 39 | if (b->IsAllocate() || b->IsInnerAllocatedObject()) { |
| 40 | // An allocation can never alias a parameter or a constant. |
| 41 | if (a->IsParameter()) return kNoAlias; |
| 42 | if (a->IsConstant()) return kNoAlias; |
| 43 | } |
| 44 | |
| 45 | // Constant objects can be distinguished statically. |
| 46 | if (a->IsConstant()) { |
| 47 | // TODO(titzer): DataEquals() is more efficient, but that's protected. |
| 48 | return a->Equals(b) ? kMustAlias : kNoAlias; |
| 49 | } |
| 50 | return kMayAlias; |
| 51 | } |
| 52 | |
| 53 | // Checks whether the objects referred to by the given instructions may |
| 54 | // ever be aliases. Note that this is more conservative than checking |
| 55 | // {Query(a, b) == kMayAlias}, since this method considers kMustAlias |
| 56 | // objects to also be may-aliasing. |
| 57 | inline bool MayAlias(HValue* a, HValue* b) { |
| 58 | return Query(a, b) != kNoAlias; |
| 59 | } |
| 60 | |
| 61 | inline bool MustAlias(HValue* a, HValue* b) { |
| 62 | return Query(a, b) == kMustAlias; |
| 63 | } |
| 64 | |
| 65 | inline bool NoAlias(HValue* a, HValue* b) { |
| 66 | return Query(a, b) == kNoAlias; |
| 67 | } |
| 68 | }; |
| 69 | |
| 70 | |
| 71 | } } // namespace v8::internal |
| 72 | |
| 73 | #endif // V8_HYDROGEN_ALIAS_ANALYSIS_H_ |