Re: [PATCH]: Add new heuristic for structure aliasing, don't create duplicate SFT's

[Diego Novillo <dnovillo at redhat dot com>]

On Tue, Mar 29, 2005 at 09:20:31PM -0500, Daniel Berlin wrote:

> Okay for mainline if it succeeds?
> 
The patch seems to be malformed.  Would you send me a new
version?  Some comments, though:

> 2005-03-29  Daniel Berlin  <dberlin@dberlin.org>
> 
> 	* params.def (PARAM_SALIAS_MAX_IMPLICIT_FIELDS): New
> 	* params.h (SALIAS_MAX_IMPLICIT_FIELDS): New
> 	* doc/invoke.texi: Documnet salias-max-implicit-fields.
s/Documnet/Document/

> --- params.def	23 Mar 2005 19:09:57 -0000	1.56
> +++ params.def	29 Mar 2005 23:44:28 -0000
> @@ -35,6 +35,14 @@ Software Foundation, 59 Temple Place - S
>  
>     Be sure to add an entry to invoke.texi summarizing the parameter.  */
>  
> +/* The maximum number of fields in a variable with only implicit uses
> +   for which structure aliasing will consider trying to track each
> +   field.  The default is 5.  */
>
I'd add more details about what 'implict uses' means in this
context.

> @@ -2837,25 +2904,36 @@ create_overlap_variables_for (tree var)
>  	}
>        /* Otherwise, create the variables.  */
>        subvars = lookup_subvars_for_var (var);
> -      up = used_portions[uid];
>        
> +      qsort (VEC_address (fieldoff_t, fieldstack), 
> +	     VEC_length (fieldoff_t, fieldstack), 
> +	     sizeof (fieldoff_t),
> +	     fieldoff_compare);
> +
>        while (VEC_length (fieldoff_t, fieldstack) != 0)
>  	{
> -	  subvar_t sv = ggc_alloc (sizeof (struct subvar));
> +	  subvar_t sv;
>  	  HOST_WIDE_INT fosize;
>  	  var_ann_t ann;
>  
>  	  fo = VEC_pop (fieldoff_t, fieldstack);	  
>  	  fosize = TREE_INT_CST_LOW (DECL_SIZE (fo->field));
>  
> -	  if ((fo->offset <= up->minused
> -	       && fo->offset + fosize <= up->minused)
> -	      || fo->offset >= up->maxused)
> +	  /* If this field isn't in the used portion,
> +	     or it has the exact same offset and size as the last
> +	     field, skip it.  */
> +
> +	  if (((fo->offset <= up->minused
> +		&& fo->offset + fosize <= up->minused)
> +	       || fo->offset >= up->maxused)
> +	      || (fo->offset == lastfooffset
> +		  && fosize == lastfosize
> +		  && currfotype == lastfotype))
>
Where is currfotype declared and initialized?  This is the
addition to avoid merging fields of different types?


>  @table @gcctabopt
> +@item salias-max-implicit-fields
> +The maximum number of fields in a variable with only implicit uses
> +for which structure aliasing will consider trying to track each
> +field.  The default is 5
>
Similar comment.  Add more details about implicit vs explicit
uses and why it affects the heuristic.


Thanks.  Diego.