Add an ArrayRef upcasting constructor from ArrayRef<U*> -> ArrayRef<T*> where T is a base of U.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225053 91177308-0d34-0410-b5e6-96231b3b80d8

unittests/ADT/ArrayRefTest.cpp

@@ -90,4 +90,39 @@ TEST(ArrayRefTest, ConstConvert) {
   a = ArrayRef<int *>(A);
 }
 
+struct A {
+  int data;
+
+  A() : data(0) {}
+};
+
+struct B : A {
+  int data2;
+
+  B() : A(), data2(0) {}
+};
+
+TEST(ArrayRefTest, UpcastConvert) {
+  B Data[5];
+
+  for (unsigned i = 0, e = 5; i != e; ++i) {
+    Data[i].data = i + 5;
+    Data[i].data2 = i + 30;
+  }
+
+  B *DataPtrs[5];
+  for (unsigned i = 0, e = 5; i != e; ++i) {
+    DataPtrs[i] = &Data[i];
+  }
+
+  ArrayRef<B *> BArray(DataPtrs, 5);
+  ArrayRef<A *> AArray(BArray);
+
+  EXPECT_TRUE(AArray.size() == 5);
+  for (unsigned i = 0, e = 5; i != e; ++i) {
+    A *a = AArray[i];
+    EXPECT_TRUE(a->data == int(i + 5));
+  }
+}
+
 } // end anonymous namespace