--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/gcc.dg/builtin-stpncpy.c	Fri Oct 27 22:46:09 2017 +0900
@@ -0,0 +1,74 @@
+/* PR tree-optimization/80669 - Bad -Wstringop-overflow warnings for stpncpy
+   { dg-do compile }
+   { dg-options "-O2 -Wall" } */
+
+#define SIZE_MAX __SIZE_MAX__
+
+typedef __SIZE_TYPE__ size_t;
+
+void sink (char*);
+
+#define stpncpy (d, s, n)  sink (__builtin_stpncpy (d, s, n))
+
+size_t value (void);
+
+size_t range (size_t min, size_t max)
+{
+  size_t val = value ();
+  return val < min || max < val ? min : val;
+}
+
+/* Verify that no warning is issued for stpncpy with constant size.  */
+void test_cst (char *d)
+{
+  __builtin_stpncpy (d, "123", 0);
+  __builtin_stpncpy (d, "123", 1);
+  __builtin_stpncpy (d, "123", 2);
+  __builtin_stpncpy (d, "123", 3);
+  __builtin_stpncpy (d, "123", 4);
+  __builtin_stpncpy (d, "123", 5);
+  __builtin_stpncpy (d, "123", 999);
+
+  size_t n = SIZE_MAX / 2;
+
+  __builtin_stpncpy (d, "123", n);
+
+  __builtin_stpncpy (d, "123", n + 1);    /* { dg-warning "specified size \[0-9\]+ exceeds maximum object size \[0-9\]+" } */
+}
+
+
+/* Verify that no warning is issued for stpncpy with size in some range.  */
+void test_rng (char *d)
+{
+#define R(min, max) range (min, max)
+
+  __builtin_stpncpy (d, "123", R (0, 1));
+  __builtin_stpncpy (d, "123", R (0, 2));
+  __builtin_stpncpy (d, "123", R (0, 3));
+  __builtin_stpncpy (d, "123", R (0, 4));
+  __builtin_stpncpy (d, "123", R (0, 5));
+
+  __builtin_stpncpy (d, "123", R (1, 2));
+  __builtin_stpncpy (d, "123", R (1, 3));
+  __builtin_stpncpy (d, "123", R (1, 4));
+  __builtin_stpncpy (d, "123", R (1, 5));
+
+  __builtin_stpncpy (d, "123", R (2, 3));
+  __builtin_stpncpy (d, "123", R (2, 4));
+  __builtin_stpncpy (d, "123", R (2, 5));
+
+  __builtin_stpncpy (d, "123", R (3, 4));
+  __builtin_stpncpy (d, "123", R (3, 5));
+
+  __builtin_stpncpy (d, "123", R (4, 5));
+
+  __builtin_stpncpy (d, "123", R (5, 6));
+
+  __builtin_stpncpy (d, "123", R (12345, 23456));
+
+  size_t n = SIZE_MAX / 2;
+
+  __builtin_stpncpy (d, "123", R (n - 1, n + 1));
+
+  __builtin_stpncpy (d, "123", R (n + 1, n + 2));   /* { dg-warning "specified size between \[0-9\]+ and \[0-9\]+ exceeds maximum object size \[0-9\]+" } */
+}