[llvm] [ArrayRef] Add constructor from iterator_range<U*> (NFC). (PR #137796)

[David Blaikie via llvm-commits]

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@@ -149,6 +149,20 @@ namespace llvm {
                  * = nullptr)
         : Data(Vec.data()), Length(Vec.size()) {}
 
+    /// Construct an ArrayRef<T> from iterator_range<U*>. This uses SFINAE
+    /// to ensure that this is only used for iterator ranges of random access
+    /// iterators that can be converted.
+    template <typename U,
+              typename = std::enable_if<
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dwblaikie wrote:

Probably still worth using `std::enable_if_t` here, but without explicitly specifying a type parameter (the default is void, so that's fine) - if you are using `std::enable_if` then I think you have to add the `::type` at the end (that's where the SFINAE is - `std::enable_if<false>` has no nested `type` member, but `std::enable_if<true>` does)

Speaking of which - perhaps you could use some static_asserts to check that this SFINAE is rejecting the relevant cases in this condition?

Also - perhaps you could explain more how this condition works? It's not clear to me it does what we want/can detect contiguous sequences.

https://github.com/llvm/llvm-project/pull/137796