[tree-ssa] RETURN_EXPR argument

[Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>]

Hello,

what is the reason for allowing the argument of a RETURN_EXPR to be a
regular modify statement?  It would IMHO be simpler to manipulate
if there was only the returned value; a comment in tree-simple.c claims
that "some of expand_return depends on getting a MODIFY_EXPR", but
the following patch passes at least c testsuite without any problems.

Zdenek

Index: gimplify.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/Attic/gimplify.c,v
retrieving revision 1.1.2.118
diff -c -3 -p -r1.1.2.118 gimplify.c
*** gimplify.c	17 Nov 2003 23:18:12 -0000	1.1.2.118
--- gimplify.c	19 Nov 2003 00:16:30 -0000
*************** gimplify_return_expr (tree stmt, tree *p
*** 867,920 ****
  #endif
      }
  
!   /* We need to pass the full MODIFY_EXPR down so that special handling
!      can replace it with something else.  */
    gimplify_stmt (&ret_expr);
- 
-   if (result == NULL_TREE)
-     TREE_OPERAND (stmt, 0) = NULL_TREE;
-   else if (ret_expr == TREE_OPERAND (stmt, 0))
-     /* It was already GIMPLE.  */
-     return GS_ALL_DONE;
-   else
-     {
-       /* If there's still a MODIFY_EXPR of the RESULT_DECL after
- 	 gimplification, find it so we can put it in the RETURN_EXPR.  */
-       tree ret = NULL_TREE;
- 
-       if (TREE_CODE (ret_expr) == STATEMENT_LIST)
- 	{
- 	  tree_stmt_iterator si;
- 	  for (si = tsi_start (ret_expr); !tsi_end_p (si); tsi_next (&si))
- 	    {
- 	      tree sub = tsi_stmt (si);
- 	      if (TREE_CODE (sub) == MODIFY_EXPR
- 		  && TREE_OPERAND (sub, 0) == result)
- 		{
- 		  ret = sub;
- 		  if (tsi_one_before_end_p (si))
- 		    tsi_delink (&si);
- 		  else
- 		    {
- 		      /* If there were posteffects after the MODIFY_EXPR,
- 			 we need a temporary.  */
- 		      tree tmp = create_tmp_var (TREE_TYPE (result), "retval");
- 		      TREE_OPERAND (ret, 0) = tmp;
- 		      ret = build (MODIFY_EXPR, TREE_TYPE (result),
- 				   result, tmp);
- 		    }
- 		  break;
- 		}
- 	    }
- 	}
- 
-       if (ret)
- 	TREE_OPERAND (stmt, 0) = ret;
-       else
- 	/* The return value must be set up some other way.  Just tell
- 	   expand_return that we're returning the RESULT_DECL.  */
- 	TREE_OPERAND (stmt, 0) = result;
-     }
  
    append_to_statement_list (ret_expr, pre_p);
    return GS_ALL_DONE;
--- 867,874 ----
  #endif
      }
  
!   TREE_OPERAND (stmt, 0) = result;
    gimplify_stmt (&ret_expr);
  
    append_to_statement_list (ret_expr, pre_p);
    return GS_ALL_DONE;