[ADT][NFC] Add extra typedefs to `ArrayRef` and `MutableArrayRef`

[vinograd47]

Summary

• value_type
• pointer
• const_pointer
• reference
• const_reference
• const_reverse_iterator
• size_type
• difference_type

It makes ArrayRef and MutableArrayRef types fully compliant with STL Container concept.

[lattner]

Thanks!

[vinograd47]

Rebased to latest main branch.

[vinograd47]

Removed std:: namespace from size_t and ptrdiff_t.

[vinograd47]

Removed const qualifier from ArrayRef::value_type.

[vinograd47]

Rebased and fixed ArrayRef typedefs

[vinograd47]

@lattner I've finalized the change and fixed CI failures. Please take a look one more time.

[vinograd47]

@courbet I saw in git history that you have had similar commit, which was reverted. Could you please take a look at this change?

[courbet]

Nice, thanks. I tried that a couple years back but had ARM buildbot errors that maintainers were not able to expain. Let's hope it goes better this time !

llvm/include/llvm/ADT/ArrayRef.h

namespace llvm {
   /// extends past that of the ArrayRef. For this reason, it is not in general
   /// safe to store an ArrayRef.
   ///
   /// This is intended to be trivially copyable, so it should be passed by
   /// value.
   template<typename T>
   class LLVM_GSL_POINTER LLVM_NODISCARD ArrayRef {
   public:
-    using iterator = const T *;
-    using const_iterator = const T *;
-    using size_type = size_t;
+    using value_type = T;
+    using pointer = value_type *;
+    using const_pointer = const value_type *;
+    using reference = value_type &;
+    using const_reference = const value_type &;
+    using iterator = const_pointer;
+    using const_iterator = const_pointer;
     using reverse_iterator = std::reverse_iterator<iterator>;
+    using const_reverse_iterator = std::reverse_iterator<const_iterator>;
+    using size_type = size_t;
+    using difference_type = ptrdiff_t;
 
   private:
     /// The start of the array, in an external buffer.
     const T *Data = nullptr;
 
     /// The number of elements.
     size_type Length = 0;
 
#endif
   /// extends past that of the MutableArrayRef. For this reason, it is not in
   /// general safe to store a MutableArrayRef.
   ///
   /// This is intended to be trivially copyable, so it should be passed by
   /// value.
   template<typename T>
   class LLVM_NODISCARD MutableArrayRef : public ArrayRef<T> {
   public:
-    using iterator = T *;
+    using value_type = T;
+    using pointer = value_type *;
+    using const_pointer = const value_type *;
+    using reference = value_type &;
+    using const_reference = const value_type &;
+    using iterator = pointer;
+    using const_iterator = const_pointer;
     using reverse_iterator = std::reverse_iterator<iterator>;
+    using const_reverse_iterator = std::reverse_iterator<const_iterator>;
+    using size_type = size_t;
+    using difference_type = ptrdiff_t;
 
     /// Construct an empty MutableArrayRef.
     /*implicit*/ MutableArrayRef() = default;
 
     /// Construct an empty MutableArrayRef from None.
     /*implicit*/ MutableArrayRef(NoneType) : ArrayRef<T>() {}
 
     /// Construct a MutableArrayRef from a single element.