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 (empty_string):  Add prototype.
	(optimize_assignment):  Set the length of an empty string
	constant to zero.

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

	PR fortran/52861
	* gfortran.dg/string_assign_1.f90:  New test case.

From-SVN: r188300

gcc/fortran/ChangeLog

+2012-06-07  Thomas König  <tkoenig@gcc.gnu.org>
+
+	PR fortran/52861
+	* frontend-passes (empty_string):  Add prototype.
+	(optimize_assignment):  Set the length of an empty string
+	constant to zero.
+
 2012-06-04  Tobias Burnus  <burnus@net-b.de>
 
 	PR fortran/50619

gcc/fortran/frontend-passes.c

 /* Pass manager for Fortran front end.
-   Copyright (C) 2010, 2011 Free Software Foundation, Inc.
+   Copyright (C) 2010, 2011, 2012 Free Software Foundation, Inc.
    Contributed by Thomas König.
 
 This file is part of GCC.
@@ -37,6 +37,7 @@ static bool optimize_comparison (gfc_expr *, gfc_intrinsic_op);
 static bool optimize_trim (gfc_expr *);
 static bool optimize_lexical_comparison (gfc_expr *);
 static void optimize_minmaxloc (gfc_expr **);
+static bool empty_string (gfc_expr *e);
 
 /* How deep we are inside an argument list.  */
 
@@ -734,10 +735,15 @@ optimize_assignment (gfc_code * c)
   lhs = c->expr1;
   rhs = c->expr2;
 
-  /* Optimize away a = trim(b), where a is a character variable.  */
-
   if (lhs->ts.type == BT_CHARACTER)
-    remove_trim (rhs);
+    {
+      /* 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))
+	rhs->value.character.length = 0;
+    }
 
   if (lhs->rank > 0 && gfc_check_dependency (lhs, rhs, true) == 0)
     optimize_binop_array_assignment (c, &rhs, false);

gcc/testsuite/ChangeLog

+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>
 
 	PR middle-end/53580

gcc/testsuite/gfortran.dg/string_assign_1.f90

+! { dg-do compile }
+! { dg-options "-ffrontend-optimize -fdump-tree-original" }
+! PR 52861 - optimize this to c = '' so that there is
+! no memcpy in the generated code.
+program main
+  character (len=20) :: c
+  c = '     '
+  print *,c
+end program main
+! { dg-final { scan-tree-dump-times "memcpy" 0 "original" } }
+! { dg-final { cleanup-tree-dump "original" } }