PR 83705 Repeat with large values

This patch fixes the regression by increasing the limit where we fall
back to runtime to 2**28 elements, which is the same limit where
previous releases failed. The are still bugs in the runtime
evaluation, so in many cases longer characters will still fail, so
print a warning message.

Regtested on x86_64-pc-linux-gnu.

gcc/fortran/ChangeLog:

2018-02-01  Janne Blomqvist  <jb@gcc.gnu.org>

	PR fortran/83705
	* simplify.c (gfc_simplify_repeat): Increase limit for deferring
	to runtime, print a warning message.

gcc/testsuite/ChangeLog:

2018-02-01  Janne Blomqvist  <jb@gcc.gnu.org>

	PR fortran/83705
	* gfortran.dg/repeat_7.f90: Catch warning message.

From-SVN: r257281

gcc/fortran/ChangeLog

+2018-02-01  Janne Blomqvist  <jb@gcc.gnu.org>
+
+	PR fortran/83705
+	* simplify.c (gfc_simplify_repeat): Increase limit for deferring
+	to runtime, print a warning message.
+
 2018-01-31  Jakub Jelinek  <jakub@redhat.com>
 
 	PR fortran/84116

gcc/fortran/simplify.c

@@ -6121,12 +6121,16 @@ gfc_simplify_repeat (gfc_expr *e, gfc_expr *n)
   len = e->value.character.length;
   gfc_charlen_t nlen = ncop * len;
 
-  /* Here's a semi-arbitrary limit. If the string is longer than 32 MB
-     (8 * 2**20 elements * 4 bytes (wide chars) per element) defer to
+  /* Here's a semi-arbitrary limit. If the string is longer than 1 GB
+     (2**28 elements * 4 bytes (wide chars) per element) defer to
      runtime instead of consuming (unbounded) memory and CPU at
      compile time.  */
-  if (nlen > 8388608)
+  if (nlen > 268435456)
+    {
+      gfc_warning_now (0, "Evaluation of string longer than 2**28 at %L"
+		       " deferred to runtime, expect bugs", &e->where);
       return NULL;
+    }
 
   result = gfc_get_character_expr (e->ts.kind, &e->where, NULL, nlen);
   for (size_t i = 0; i < (size_t) ncop; i++)

gcc/testsuite/ChangeLog

+2018-02-01  Janne Blomqvist  <jb@gcc.gnu.org>
+
+	PR fortran/83705
+	* gfortran.dg/repeat_7.f90: Catch warning message.
+
 2018-01-31  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>
 
 	* lib/target-supports.exp (check_effective_target_comdat_group):

gcc/testsuite/gfortran.dg/repeat_7.f90

@@ -4,5 +4,5 @@
 ! compile time.
 program p
   character, parameter :: z = 'z'
-  print *, repeat(z, huge(1_4))
+  print *, repeat(z, huge(1_4)) ! { dg-warning "Evaluation of string" }
 end program p