re PR fortran/50409 (SIGSEGV in gfc_simplify_expr)

	PR fortran/50409
	* expr.c (gfc_simplify_expr): Substrings can't have negative
	length.
	* gcc/testsuite/gfortran.dg/string_5.f90: Improve testcase.

From-SVN: r181181

gcc/fortran/ChangeLog

 2011-11-08  Francois-Xavier Coudert  <fxcoudert@gcc.gnu.org>
 
+	PR fortran/50409
+	* expr.c (gfc_simplify_expr): Substrings can't have negative
+	length.
+
+2011-11-08  Francois-Xavier Coudert  <fxcoudert@gcc.gnu.org>
+
 	PR fortran/50334
 	* invoke.texi (-finit-*): Document interaction with
 	-Wuninitialized.

gcc/fortran/expr.c

@@ -1853,8 +1853,8 @@ gfc_simplify_expr (gfc_expr *p, int type)
 	  if (p->ref && p->ref->u.ss.end)
 	    gfc_extract_int (p->ref->u.ss.end, &end);
 
-	  if (end < 0)
-	    end = 0;
+	  if (end < start)
+	    end = start;
 
 	  s = gfc_get_wide_string (end - start + 2);
 	  memcpy (s, p->value.character.string + start,

gcc/testsuite/ChangeLog

+2011-11-08  Francois-Xavier Coudert  <fxcoudert@gcc.gnu.org>
+
+	PR fortran/50409
+	* gcc/testsuite/gfortran.dg/string_5.f90: Improve testcase.
+
 2011-10-23  Jason Merrill  <jason@redhat.com>
 
 	PR c++/50835

gcc/testsuite/gfortran.dg/string_5.f90

 ! { dg-do compile }
-! PR fortran/48876 - this used to segfault.
-! Test case contributed by mhp77 (a) gmx.at.
 program test
+
+  ! PR fortran/48876 - this used to segfault.
+  ! Test case contributed by mhp77 (a) gmx.at.
   character ::  string =  "string"( : -1 )
+
+  ! PR fortran/50409
+  character v(3)
+  v = (/ ('123'(i:1), i = 3, 1, -1) /) 
+  print *, v
+
 end program test