CSE2410 Fall 2014 Bounce

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#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;

  }

};

} }  // namespace v8::internal

#endif  // V8_HYDROGEN_ALIAS_ANALYSIS_H_