--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/g++.dg/cpp2a/comma5.C	Thu Feb 13 11:34:05 2020 +0900
@@ -0,0 +1,21 @@
+// PR c++/91391 - bogus -Wcomma-subscript warning.
+// { dg-do compile { target c++2a } }
+
+template<typename T, typename U>
+int foo(T t, U u) { return t + u; }
+
+void
+fn (int *a, int b, int c)
+{
+  a[foo<int, int>(1, 2)];
+  a[foo<int, int>(1, 2), foo<int, int>(3, 4)]; // { dg-warning "24:top-level comma expression in array subscript is deprecated" }
+
+  a[b < c, b < c]; // { dg-warning "top-level comma expression in array subscript is deprecated" }
+  a[b < c, b > c]; // { dg-warning "top-level comma expression in array subscript is deprecated" }
+  a[b > c, b > c]; // { dg-warning "top-level comma expression in array subscript is deprecated" }
+  a[b > c, b < c]; // { dg-warning "top-level comma expression in array subscript is deprecated" }
+  a[(b < c, b < c)];
+  a[(b < c, b > c)];
+  a[b << c, b << c]; // { dg-warning "top-level comma expression in array subscript is deprecated" }
+  a[(b << c, b << c)]; 
+}