re PR fortran/52861 ((missed optimisation) missed transformation to memset with -O3)

2012-06-07  Thomas König  <tkoenig@gcc.gnu.org>

	PR fortran/52861
	* frontend-passes.c (optimize_assignment):  Don't set the
	length of an empty string for deferred-length character
	variables.

2012-06-07  Thomas König  <tkoenig@gcc.gnu.org>

	PR fortran/52861
	* gfortran.dg/string_assign_2.f90:  New test case.

From-SVN: r188305

gcc/fortran/ChangeLog

 2012-06-07  Thomas König  <tkoenig@gcc.gnu.org>
 
 	PR fortran/52861
-	* frontend-passes (empty_string):  Add prototype.
+	* frontend-passes.c (optimize_assignment):  Don't set the
+	length of an empty string for deferred-length character
+	variables.
+
+2012-06-07  Thomas König  <tkoenig@gcc.gnu.org>
+
+	PR fortran/52861
+	* frontend-passes.c (empty_string):  Add prototype.
 	(optimize_assignment):  Set the length of an empty string
 	constant to zero.
 

gcc/fortran/frontend-passes.c

@@ -740,8 +740,10 @@ optimize_assignment (gfc_code * c)
       /* Optimize away a = trim(b), where a is a character variable.  */
       remove_trim (rhs);
 
-      /* Replace a = '   ' by a = '' to optimize away a memcpy.  */
-      if (empty_string(rhs))
+      /* Replace a = '   ' by a = '' to optimize away a memcpy, but only
+	 for strings with non-deferred length (otherwise we would
+	 reallocate the length.  */
+      if (empty_string(rhs) && ! lhs->ts.deferred)
 	rhs->value.character.length = 0;
     }
 

gcc/testsuite/ChangeLog

 2012-06-07  Thomas König  <tkoenig@gcc.gnu.org>
 
 	PR fortran/52861
+	* gfortran.dg/string_assign_2.f90:  New test case.
+
+2012-06-07  Thomas König  <tkoenig@gcc.gnu.org>
+
+	PR fortran/52861
 	* gfortran.dg/string_assign_1.f90:  New test case.
 
 2012-06-07  Jakub Jelinek  <jakub@redhat.com>

gcc/testsuite/gfortran.dg/string_assign_2.f90

+! { dg-do run }
+! { dg-options "-ffrontend-optimize" }
+program main
+  character (len=:), allocatable :: a
+  a = 'a'
+  if (len(a) /= 1) call abort
+  a = '  '
+  if (len(a) /= 2) call abort
+end program main