Add hashing and DenseMapInfo for ArrayRef

[• espindola]

Summary

Sometimes it is more natural to use a ArrayRef<uint8_t> than a StringRef to represent a range of bytes that is not, semantically, a string.

[dblaikie]

Looks good! (optional unit tests - no doubt similar things don't bother
with them - but could be nice)

include/llvm/ADT/ArrayRef.h

 //===--- ArrayRef.h - Array Reference Wrapper -------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_ADT_ARRAYREF_H
 #define LLVM_ADT_ARRAYREF_H
 
+#include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/None.h"
 #include "llvm/ADT/SmallVector.h"
 #include <vector>
 
 namespace llvm {
 
   /// ArrayRef - Represent a constant reference to an array (0 or more elements
   /// consecutively in memory), i.e. a start pointer and a length.  It allows
namespace llvm {
 
   /// @}
 
   // ArrayRefs can be treated like a POD type.
   template <typename T> struct isPodLike;
   template <typename T> struct isPodLike<ArrayRef<T> > {
     static const bool value = true;
   };
+
+  template <typename T> hash_code hash_value(ArrayRef<T> S) {
+    return hash_combine_range(S.begin(), S.end());
+  }
 }
 
 #endif

include/llvm/ADT/DenseMapInfo.h

 //===- llvm/ADT/DenseMapInfo.h - Type traits for DenseMap -------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file defines DenseMapInfo traits for DenseMap.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_ADT_DENSEMAPINFO_H
 #define LLVM_ADT_DENSEMAPINFO_H
 
+#include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/PointerLikeTypeTraits.h"
 #include "llvm/Support/type_traits.h"
 
 namespace llvm {
 
 template<typename T>
static bool isEqual(StringRef LHS, StringRef RHS) {
     if (RHS.data() == getEmptyKey().data())
       return LHS.data() == getEmptyKey().data();
     if (RHS.data() == getTombstoneKey().data())
       return LHS.data() == getTombstoneKey().data();
     return LHS == RHS;
   }
 };
 
+// Provide DenseMapInfo for ArrayRefs.
+template <typename T> struct DenseMapInfo<ArrayRef<T>> {
+  static inline ArrayRef<T> getEmptyKey() {
+    return ArrayRef<T>(reinterpret_cast<const T *>(~static_cast<uintptr_t>(0)),
+                       size_t(0));
+  }
+  static inline ArrayRef<T> getTombstoneKey() {
+    return ArrayRef<T>(reinterpret_cast<const T *>(~static_cast<uintptr_t>(1)),
+                       size_t(0));
+  }
+  static unsigned getHashValue(ArrayRef<T> Val) {
+    assert(Val.data() != getEmptyKey().data() && "Cannot hash the empty key!");
+    assert(Val.data() != getTombstoneKey().data() &&
+           "Cannot hash the tombstone key!");
+    return (unsigned)(hash_value(Val));
+  }
+  static bool isEqual(ArrayRef<T> LHS, ArrayRef<T> RHS) {
+    if (RHS.data() == getEmptyKey().data())
+      return LHS.data() == getEmptyKey().data();
+    if (RHS.data() == getTombstoneKey().data())
+      return LHS.data() == getTombstoneKey().data();
+    return LHS == RHS;
+  }
+};
+
 } // end namespace llvm
 
 #endif