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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_CRANKSHAFT_HYDROGEN_ALIAS_ANALYSIS_H_
6 : #define V8_CRANKSHAFT_HYDROGEN_ALIAS_ANALYSIS_H_
7 :
8 : #include "src/crankshaft/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 6368759 : HAliasing Query(HValue* a, HValue* b) {
28 : // The same SSA value always references the same object.
29 6368759 : if (a == b) return kMustAlias;
30 :
31 10182760 : if (a->IsAllocate() || a->IsInnerAllocatedObject()) {
32 : // Two non-identical allocations can never be aliases.
33 311694 : if (b->IsAllocate()) return kNoAlias;
34 188009 : if (b->IsInnerAllocatedObject()) return kNoAlias;
35 : // An allocation can never alias a parameter or a constant.
36 184429 : if (b->IsParameter()) return kNoAlias;
37 172015 : if (b->IsConstant()) return kNoAlias;
38 : }
39 9832975 : if (b->IsAllocate() || b->IsInnerAllocatedObject()) {
40 : // An allocation can never alias a parameter or a constant.
41 175843 : if (a->IsParameter()) return kNoAlias;
42 169095 : if (a->IsConstant()) return kNoAlias;
43 : }
44 :
45 : // Constant objects can be distinguished statically.
46 4891439 : if (a->IsConstant()) {
47 1912818 : return a->Equals(b) ? kMustAlias : kNoAlias;
48 : }
49 : return kMayAlias;
50 : }
51 :
52 : // Checks whether the objects referred to by the given instructions may
53 : // ever be aliases. Note that this is more conservative than checking
54 : // {Query(a, b) == kMayAlias}, since this method considers kMustAlias
55 : // objects to also be may-aliasing.
56 : inline bool MayAlias(HValue* a, HValue* b) {
57 207486 : return Query(a, b) != kNoAlias;
58 : }
59 :
60 : inline bool MustAlias(HValue* a, HValue* b) {
61 6161319 : return Query(a, b) == kMustAlias;
62 : }
63 :
64 : inline bool NoAlias(HValue* a, HValue* b) {
65 : return Query(a, b) == kNoAlias;
66 : }
67 : };
68 :
69 :
70 : } // namespace internal
71 : } // namespace v8
72 :
73 : #endif // V8_CRANKSHAFT_HYDROGEN_ALIAS_ANALYSIS_H_
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