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// Copyright 2013 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_CRANKSHAFT_HYDROGEN_ALIAS_ANALYSIS_H_
#define V8_CRANKSHAFT_HYDROGEN_ALIAS_ANALYSIS_H_
#include "src/crankshaft/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;
}
};
} // namespace internal
} // namespace v8
#endif // V8_CRANKSHAFT_HYDROGEN_ALIAS_ANALYSIS_H_
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