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// 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_
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