[patch] Improve gimplification of constructors

[Eric Botcazou <ebotcazou at adacore dot com>]

Hi,

attached is a couple of patches to improve gimplification of constructors:

 1. We don't need to pre-evaluate anything if it's a real init (INIT_EXPR).

 2. categorize_ctor_elements doesn't correctly count the number of scalars 
when the constructor is not constant, so

	/* ??? This bit ought not be needed.  For any element not present
	   in the initializer, we should simply set them to zero.  Except
	   we'd need to *find* the elements that are not present, and that
	   requires trickery to avoid quadratic compile-time behavior in
	   large cases or excessive memory use in small cases.  */
	else if (num_ctor_elements < num_type_elements)
	  cleared = true;

unnecessarily triggers and causes useless clearing, for example on

procedure P is

  type Arr is array (1..2) of Character;
  function F return Arr;
  pragma Import (Ada, F);

  type Rec is record
    A : Arr;
  end record;

  A : Rec := (A => F);

begin
  null;
end;

Bootstrapped/regtested on x86_64-suse-linux, OK for mainline?


2010-04-09  Eric Botcazou  <ebotcazou@adacore.com>

	* gimplify.c (gimplify_init_constructor): Do not pre-evaluate if this
	is a real initialization.

	* expr.c (categorize_ctor_elements_1): Properly count sub-elements of
	non-constant aggregate elements.


-- 
Eric Botcazou

Index: expr.c
===================================================================
--- expr.c	(revision 158148)
+++ expr.c	(working copy)
@@ -4861,9 +4861,8 @@ categorize_ctor_elements_1 (const_tree c
 
   FOR_EACH_CONSTRUCTOR_ELT (CONSTRUCTOR_ELTS (ctor), idx, purpose, value)
     {
-      HOST_WIDE_INT mult;
+      HOST_WIDE_INT mult = 1;
 
-      mult = 1;
       if (TREE_CODE (purpose) == RANGE_EXPR)
 	{
 	  tree lo_index = TREE_OPERAND (purpose, 0);
@@ -4925,12 +4924,17 @@ categorize_ctor_elements_1 (const_tree c
 	  break;
 
 	default:
-	  nz_elts += mult;
-	  elt_count += mult;
+	  {
+	    HOST_WIDE_INT tc = count_type_elements (TREE_TYPE (value), true);
+	    if (tc < 1)
+	      tc = 1;
+	    nz_elts += mult * tc;
+	    elt_count += mult * tc;
 
-	  if (const_from_elts_p && const_p)
-	    const_p = initializer_constant_valid_p (value, TREE_TYPE (value))
-		      != NULL_TREE;
+	    if (const_from_elts_p && const_p)
+	      const_p = initializer_constant_valid_p (value, TREE_TYPE (value))
+			!= NULL_TREE;
+	  }
 	  break;
 	}
     }

Index: gimplify.c
===================================================================
--- gimplify.c	(revision 158148)
+++ gimplify.c	(working copy)
@@ -3793,10 +3793,10 @@ gimplify_init_constructor (tree *expr_p,
 	if (notify_temp_creation)
 	  return GS_OK;
 
-	/* If there are nonzero elements, pre-evaluate to capture elements
-	   overlapping with the lhs into temporaries.  We must do this before
-	   clearing to fetch the values before they are zeroed-out.  */
-	if (num_nonzero_elements > 0)
+	/* If there are nonzero elements and if needed, pre-evaluate to capture
+	   elements overlapping with the lhs into temporaries.  We must do this
+	   before clearing to fetch the values before they are zeroed-out.  */
+	if (num_nonzero_elements > 0 && TREE_CODE (*expr_p) != INIT_EXPR)
 	  {
 	    preeval_data.lhs_base_decl = get_base_address (object);
 	    if (!DECL_P (preeval_data.lhs_base_decl))