PR tree-optimization/91914 - Invalid strlen folding for offset into struct

gcc/testsuite/CHangeLog:
	* gcc.dg/strlenopt-79.c: New test.

From-SVN: r276156

gcc/testsuite/ChangeLog

+2019-09-26  Martin Sebor  <msebor@redhat.com>
+
+	PR tree-optimization/91914
+	* gcc.dg/strlenopt-79.c: New test.
+
 2019-09-26  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
 
 	* gcc.target/arm/acle/simd32.c: Update test.

gcc/testsuite/gcc.dg/strlenopt-79.c

+/* PR tree-optimization/91914 - Invalid strlen folding for offset into struct
+   { dg-do run }
+   { dg-options "-O2 -Wall" } */
+
+#define assert(expr)						\
+  ((expr)							\
+   ? (void)0							\
+   : (__builtin_printf ("%s:%i: assertion failed: %s\n",	\
+			__FILE__, __LINE__, #expr),		\
+      __builtin_abort ()))
+
+extern __SIZE_TYPE__ strlen (const char*);
+
+struct stringpool_t
+{
+  char s1[sizeof ("1")];
+  char s2[sizeof ("12")];
+  char s3[sizeof ("123")];
+  char s4[sizeof ("1234")];
+  char s5[sizeof ("12345")];
+};
+
+static const struct stringpool_t stringpool_contents =
+  {
+   "1", "12", "123", "1234", "12345"
+  };
+
+#define stringpool ((const char *) &stringpool_contents)
+
+volatile int i0 = 0, i2 = 2, i5 = 5, i9 = 9, i14 = 14;
+
+int main (void)
+{
+  /* These shouldn't trigger warnings.  */
+  assert (strlen (stringpool) == 1);
+  assert (strlen (stringpool + 2) == 2);
+  assert (strlen (stringpool + 5) == 3);
+  assert (strlen (stringpool + 9) == 4);
+  assert (strlen (stringpool + 14) == 5);
+
+  assert (strlen (stringpool + i0) == 1);
+  assert (strlen (stringpool + i2) == 2);
+  assert (strlen (stringpool + i5) == 3);
+  assert (strlen (stringpool + i9) == 4);
+  assert (strlen (stringpool + i14) == 5);
+}