--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/gcc.dg/tree-ssa/strncat.c	Thu Oct 25 07:37:49 2018 +0900
@@ -0,0 +1,35 @@
+/* PR tree-optimization/83075 - Invalid strncpy optimization */
+/* { dg-do run } */
+/* { dg-options "-O2 -Wstringop-overflow" } */
+
+typedef __SIZE_TYPE__ size_t;
+
+__attribute__((noipa)) size_t
+foo (char *p, char *q, size_t *r)
+{
+  size_t n0 = __builtin_strlen (p);
+  __builtin_strncat (q, p, n0);		/* { dg-warning "specified bound depends on the length" } */
+  size_t n1 = __builtin_strlen (p);
+  *r = n0;
+  return n1;
+}
+
+int
+main ()
+{
+  char a[8] = "";
+  __builtin_strcpy (a, "123");
+  size_t n0 = __builtin_strlen (a);
+  __builtin_strncat (a + 3, a, n0);	/* { dg-warning "specified bound depends on the length" } */
+  size_t n1 = __builtin_strlen (a);
+  if (n1 == n0)
+    __builtin_abort ();
+  a[6] = '7';
+  __builtin_strcpy (a, "456");
+  size_t n2;
+  if (foo (a, a + 3, &n2) != 6 || n2 != 3)
+    __builtin_abort ();
+  if (__builtin_memcmp (a, "456456\0", sizeof "456456\0"))
+    __builtin_abort ();
+  return 0;
+}