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
10namespace v8 {
11namespace internal {
12
13enum 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.
23class 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_
74