!fixup simplify SFINAE check

Author: fhahn

llvm/include/llvm/ADT/ArrayRef.h

@@ -150,16 +150,9 @@ namespace llvm {
         : 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<
-                  std::is_base_of<
-                      std::random_access_iterator_tag,
-                      typename std::iterator_traits<
-                          decltype(std::declval<const iterator_range<U *> &>()
-                                       .begin())>::iterator_category>::value &&
-                  std::is_convertible_v<U *, T const *>>>
+    /// to ensure that this is only used for iterator ranges over plain pointer
+    /// iterators.
+    template <typename U, typename = std::enable_if_t<std::is_same_v<U *, T *>>>
     ArrayRef(const iterator_range<U *> &Range)
         : Data(Range.begin()), Length(llvm::size(Range)) {}
 

llvm/unittests/ADT/ArrayRefTest.cpp

@@ -255,6 +255,20 @@ TEST(ArrayRefTest, ArrayRefFromStdArray) {
   }
 }
 
+struct TestRandomAccessIterator {
+  using iterator_category = std::random_access_iterator_tag;
+};
+
+static_assert(
+    !std::is_constructible<ArrayRef<int>,
+                           iterator_range<TestRandomAccessIterator>>::value,
+    "cannot construct from iterator range with non-pointer iterator");
+static_assert(!std::is_constructible<ArrayRef<int>, iterator_range<int>>::value,
+              "cannot construct from iterator range with non-pointer iterator");
+static_assert(
+    std::is_constructible<ArrayRef<char *>, iterator_range<char **>>::value,
+    "should be able to construct ArrayRef from iterator_range over pointers");
+
 TEST(ArrayRefTest, ArrayRefFromIteratorRange) {
   std::array<int, 5> A1{{42, -5, 0, 1000000, -1000000}};
   ArrayRef<int> A2 = make_range(A1.begin(), A1.end());