Re: [patch, RFC. Fortran] Some clobbering for INTENT(OUT) arrays

[Mikael Morin]

Hello,

Le 02/10/2022 à 22:07, Thomas Koenig via Fortran a écrit :


I am a bit stuck of how to generate a reference to the first element
of the array (really, just dereferencing the data pointer)
in the most elegant way.  I am currently leaning towards
building a gfc_expr, which should work, but would be less
than elegant.

So, anything more elegant at hand?


I don't understand why you are trying to do this.
According to Richi [1], array references are not allowed, so you can 
(and actually have to) pick the full variable decl directly.


[1] https://gcc.gnu.org/pipermail/fortran/2022-September/058181.html

A few comments about the rest...


What happens if the

+ if (!sym->attr.allocatable && !sym->attr.pointer
+ && !POINTER_TYPE_P (TREE_TYPE (sym->backend_decl)))


part is taken out is that the whole descriptor can be clobbered in
such a case, which is of course not what is wanted. 


The canonical way is to look for GFC_DESCRIPTOR_TYPE_P (TREE_TYPE (...)).
Your way should work in most cases, but there are twisted cases for 
which I'm not sure (assumed shape arrays with the value attribute).



diff --git a/gcc/fortran/trans-expr.cc b/gcc/fortran/trans-expr.cc
index 4f3ae82d39c..bbb00f90a77 100644
--- a/gcc/fortran/trans-expr.cc
+++ b/gcc/fortran/trans-expr.cc
@@ -6896,10 +6897,23 @@ gfc_conv_procedure_call (gfc_se * se, gfc_symbol * sym,
 fsym->attr.pointer);
}
  else
-   /* This is where we introduce a temporary to store the
-  result of a non-lvalue array expression.  */
-   gfc_conv_array_parameter (, e, nodesc_arg, fsym,
- sym->name, NULL);
+   {
+ /* This is where we introduce a temporary to store the
+result of a non-lvalue array expression.  */
+ gfc_conv_array_parameter (, e, nodesc_arg, fsym,
+   sym->name, NULL);
+ if (fsym && fsym->attr.intent == INTENT_OUT
+ && gfc_full_array_ref_p (e->ref, NULL))


The scalar case has a few more conditions this seems to miss.
e->expr_type == EXPR_VARIABLE at least, but also e->ts.type != 
CHARACTER, alloc_comp and finalizable derived types, etc.



+   clobber_array
+ = gfc_build_array_ref 
(e->symtree->n.sym->backend_decl,
+build_int_cst (size_type_node, 
0),
+NULL_TREE, true, NULL_TREE);


This is picking the decl from the frontend data.
This proved to be problematic in the scalar case, so maybe it would be 
better to pick the variable to be clobbered from parmse.expr.
Admittedly I'm not too sure about this, arrays are much more difficult 
to work with (and to think about).



@@ -6952,6 +6966,13 @@ gfc_conv_procedure_call (gfc_se * se, gfc_symbol * sym,
   tmp, build_empty_stmt (input_location));
  gfc_add_expr_to_block (>pre, tmp);
}
+
+ if (clobber_array != NULL_TREE)
+   {
+ tree clobber;
+ clobber = build_clobber (TREE_TYPE(clobber_array));
+ gfc_add_modify (, clobber_array, clobber);
+   }
}
}
   /* Special case for an assumed-rank dummy argument. */


This can be moved to the preceding hunk.

[patch, RFC. Fortran] Some clobbering for INTENT(OUT) arrays

[Thomas Koenig via Gcc-patches]

Hi,

following Mikael's recent patch series, here is a first idea
of what extending clobbering to arrays wold look like.

The attached patch works for a subset of cases, for example

program main
  implicit none
  interface
subroutine foo(a)
  integer, intent(out) :: a(*)
end subroutine foo
  end interface
  integer, dimension(10) :: a
  call foo(a)
end program main

and

program main
  implicit none
  interface
subroutine foo(a)
  integer, intent(out) :: a(:)
end subroutine foo
  end interface
  integer, dimension(10) :: a
  a(1) = 32
  a(2) = 32
  call foo(a)
end program main

but it does not cover cases like an assumed-size array
being handed down to an INTENT(OUT) argument.

What happens if the

+ if (!sym->attr.allocatable && !sym->attr.pointer
+ && !POINTER_TYPE_P (TREE_TYPE 
(sym->backend_decl)))



part is taken out is that the whole descriptor can be clobbered in
such a case, which is of course not what is wanted.

I am a bit stuck of how to generate a reference to the first element
of the array (really, just dereferencing the data pointer)
in the most elegant way.  I am currently leaning towards
building a gfc_expr, which should work, but would be less
than elegant.

So, anything more elegant at hand?

Best regards

Thomasdiff --git a/gcc/fortran/trans-expr.cc b/gcc/fortran/trans-expr.cc
index 4f3ae82d39c..bbb00f90a77 100644
--- a/gcc/fortran/trans-expr.cc
+++ b/gcc/fortran/trans-expr.cc
@@ -43,6 +43,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "gimplify.h"
 #include "tm.h"		/* For CHAR_TYPE_SIZE.  */
 
+#include "debug.h"
 
 /* Calculate the number of characters in a string.  */
 
@@ -5981,7 +5982,6 @@ post_call:
 gfc_add_block_to_block (>post, );
 }
 
-
 /* Generate code for a procedure call.  Note can return se->post != NULL.
If se->direct_byref is set then se->expr contains the return parameter.
Return nonzero, if the call has alternate specifiers.
@@ -6099,6 +6099,7 @@ gfc_conv_procedure_call (gfc_se * se, gfc_symbol * sym,
 {
   bool finalized = false;
   tree derived_array = NULL_TREE;
+  tree clobber_array = NULL_TREE;
 
   e = arg->expr;
   fsym = formal ? formal->sym : NULL;
@@ -6896,10 +6897,23 @@ gfc_conv_procedure_call (gfc_se * se, gfc_symbol * sym,
 	 fsym->attr.pointer);
 		}
 	  else
-		/* This is where we introduce a temporary to store the
-		   result of a non-lvalue array expression.  */
-		gfc_conv_array_parameter (, e, nodesc_arg, fsym,
-	  sym->name, NULL);
+		{
+		  /* This is where we introduce a temporary to store the
+		 result of a non-lvalue array expression.  */
+		  gfc_conv_array_parameter (, e, nodesc_arg, fsym,
+	sym->name, NULL);
+		  if (fsym && fsym->attr.intent == INTENT_OUT
+		  && gfc_full_array_ref_p (e->ref, NULL))
+		{
+		  gfc_symbol *sym = e->symtree->n.sym;
+		  if (!sym->attr.allocatable && !sym->attr.pointer
+			  && !POINTER_TYPE_P (TREE_TYPE (sym->backend_decl)))
+			clobber_array
+			  = gfc_build_array_ref (e->symtree->n.sym->backend_decl,
+		 build_int_cst (size_type_node, 0),
+		 NULL_TREE, true, NULL_TREE);
+		}
+		}
 
 	  /* If an ALLOCATABLE dummy argument has INTENT(OUT) and is
 		 allocated on entry, it must be deallocated.
@@ -6952,6 +6966,13 @@ gfc_conv_procedure_call (gfc_se * se, gfc_symbol * sym,
    tmp, build_empty_stmt (input_location));
 		  gfc_add_expr_to_block (>pre, tmp);
 		}
+
+	  if (clobber_array != NULL_TREE)
+		{
+		  tree clobber;
+		  clobber = build_clobber (TREE_TYPE(clobber_array));
+		  gfc_add_modify (, clobber_array, clobber);
+		}
 	}
 	}
   /* Special case for an assumed-rank dummy argument. */