[patch, fortran] Clobber some intent(out) variables on call

[patch, fortran] Clobber some intent(out) variables on call

[Thomas Koenig]

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Hello world,

the attached patch lets the middle-end know that variables
associated with intent(out) arguments become undefined, by
issuing an assignment to a special value (a "clobber")
before entering the procedure.

Originally, I had also planned to do so on entry to the
procedure, see https://gcc.gnu.org/ml/fortran/2018-09/msg00148.html .
This turned out to cause regressions; some details are outlined
in the PR.

Regression-tested. OK for trunk?

Regards

	Thomas

2018-09-22  Thomas Koenig  <tkoenig@gcc.gnu.org>

         PR fortran/41453
         * trans.h (gfc_conv_expr_reference): Add optional argument
         add_clobber to prototype.
         (gfc_conv_procedure_call):  Set add_clobber argument to
         gfc_conv_procedure_reference to true for scalar, INTENT(OUT),
         non-pointer, non-allocatable, non-dummy variables whose type
         is neither BT_CHARACTER, BT_DERIVED or BT_CLASS, but only if
         the procedure is not elemental.
         * trans-expr.c (gfc_conv_procedure_reference): Add clobber
         statement before call if add_clobber is set.

2018-09-22  Thomas Koenig  <tkoenig@gcc.gnu.org>

         PR fortran/41453
         * gfortran.dg/intent_optimize_2.f90: New test.

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Index: trans-expr.c
===================================================================
--- trans-expr.c	(Revision 264487)
+++ trans-expr.c	(Arbeitskopie)
@@ -5276,8 +5276,17 @@ gfc_conv_procedure_call (gfc_se * se, gfc_symbol *
 			}
 		    }
 		  else
-		    gfc_conv_expr_reference (&parmse, e);
+		    {
+		      bool add_clobber;
+		      add_clobber = fsym && fsym->attr.intent == INTENT_OUT
+			&& !fsym->attr.allocatable && !fsym->attr.pointer
+			&& !e->symtree->n.sym->attr.pointer
+			&& !e->symtree->n.sym->attr.dummy  /* See PR 41453.  */
+			&& e->ts.type != BT_CHARACTER && e->ts.type != BT_DERIVED
+			&& e->ts.type != BT_CLASS && !sym->attr.elemental;
 
+		      gfc_conv_expr_reference (&parmse, e, add_clobber);
+		    }
 		  /* Catch base objects that are not variables.  */
 		  if (e->ts.type == BT_CLASS
 			&& e->expr_type != EXPR_VARIABLE
@@ -8060,7 +8069,7 @@ gfc_conv_expr_type (gfc_se * se, gfc_expr * expr,
    values only.  */
 
 void
-gfc_conv_expr_reference (gfc_se * se, gfc_expr * expr)
+gfc_conv_expr_reference (gfc_se * se, gfc_expr * expr, bool add_clobber)
 {
   gfc_ss *ss;
   tree var;
@@ -8100,6 +8109,16 @@ void
 	  gfc_add_block_to_block (&se->pre, &se->post);
 	  se->expr = var;
 	}
+      else if (add_clobber)
+	{
+	  tree clobber;
+	  tree var;
+	  /* FIXME: This fails if var is passed by reference, see PR
+	     41453.  */
+	  var = expr->symtree->n.sym->backend_decl;
+	  clobber = build_clobber (TREE_TYPE (var));
+	  gfc_add_modify (&se->pre, var, clobber);
+	}
       return;
     }
 
Index: trans.h
===================================================================
--- trans.h	(Revision 264487)
+++ trans.h	(Arbeitskopie)
@@ -485,7 +485,8 @@ tree gfc_build_compare_string (tree, tree, tree, t
 void gfc_conv_expr (gfc_se * se, gfc_expr * expr);
 void gfc_conv_expr_val (gfc_se * se, gfc_expr * expr);
 void gfc_conv_expr_lhs (gfc_se * se, gfc_expr * expr);
-void gfc_conv_expr_reference (gfc_se * se, gfc_expr *);
+void gfc_conv_expr_reference (gfc_se * se, gfc_expr * expr,
+			      bool add_clobber = false);
 void gfc_conv_expr_type (gfc_se * se, gfc_expr *, tree);
 
 

[-- Attachment #3: intent_optimize_2.f90 --]
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! { dg-do compile }
! { dg-options "-O -fno-inline -fdump-tree-optimized -fdump-tree-original" }
! PR fortran/41453
! Check that there is one clobber in the *.original tree, plus that
! the constant 123456789 has been removed tue to the INTENT(OUT).

module x
implicit none
contains
  subroutine foo(a)
    integer, intent(out) :: a
    a = 42
  end subroutine foo
end module x

program main
  use x
  implicit none
  integer :: a
  a = 12345689
  call foo(a)
  print *,a
end program main

! { dg-final { scan-tree-dump-times "123456789" 0 "optimized" } }
! { dg-final { scan-tree-dump-times "CLOBBER" 1 "original" } }

Re: [patch, fortran] Clobber some intent(out) variables on call

[Jerry DeLisle]

Minor typo, see below.

On 9/22/18 10:23 AM, Thomas Koenig wrote:
> Hello world,
> 
> the attached patch lets the middle-end know that variables
> associated with intent(out) arguments become undefined, by
> issuing an assignment to a special value (a "clobber")
> before entering the procedure.
> 
> Originally, I had also planned to do so on entry to the
> procedure, see https://gcc.gnu.org/ml/fortran/2018-09/msg00148.html .
> This turned out to cause regressions; some details are outlined
> in the PR.
> 
> Regression-tested. OK for trunk?
> 

! { dg-do compile }
! { dg-options "-O -fno-inline -fdump-tree-optimized -fdump-tree-original" }
! PR fortran/41453
! Check that there is one clobber in the *.original tree, plus that
! the constant 123456789 has been removed tue to the INTENT(OUT).

s/tue/due/

and

program main
   use x
   implicit none
   integer :: a
   a = 12345689  <---- missing 7 digit?
   call foo(a)
   print *,a
end program main

Otherwise OK.

Jerry

Re: [patch, fortran] Clobber some intent(out) variables on call

[Thomas Koenig]

Hi Jerry,

> s/tue/due/   

> a = 12345689  <---- missing 7 digit?

Yep, you're right. Corrected, committed as r264506.

Regards

	Thomas