Re: [PATCH] options, lto: Optimize streaming of optimization nodes

[Richard Biener <rguenther@suse.de>]

On Mon, 14 Sep 2020, Jakub Jelinek wrote:

> On Mon, Sep 14, 2020 at 09:31:52AM +0200, Richard Biener wrote:
> > But does it make any noticable difference in the end?  Using
> 
> Yes.
> 
> > bp_pack_var_len_unsigned just causes us to [u]leb encode half-bytes
> > rather than full bytes.  Using hardcoded 8/16/32/64 makes it still
> > dependent on what 'int' is at maximum on the host.
> > 
> > That is, I'd indeed prefer bp_pack_var_len_unsigned over hard-coding
> > 8, 16, etc., but can you share a size comparison of the bitpack?
> > I guess with bp_pack_var_len_unsigned it might shrink in half
> > compared to the current code and streaming standard -O2?
> 
> So, I've tried
> --- gcc/tree-streamer-out.c.jj	2020-07-28 15:39:10.079755251 +0200
> +++ gcc/tree-streamer-out.c	2020-09-14 10:31:29.106957258 +0200
> @@ -489,7 +489,11 @@ streamer_write_tree_bitfields (struct ou
>      pack_ts_translation_unit_decl_value_fields (ob, &bp, expr);
>  
>    if (CODE_CONTAINS_STRUCT (code, TS_OPTIMIZATION))
> +{
> +long ts = ob->main_stream->total_size;
>      cl_optimization_stream_out (ob, &bp, TREE_OPTIMIZATION (expr));
> +fprintf (stderr, "total_size %ld\n", (long) (ob->main_stream->total_size - ts));
> +}
>  
>    if (CODE_CONTAINS_STRUCT (code, TS_CONSTRUCTOR))
>      bp_pack_var_len_unsigned (&bp, CONSTRUCTOR_NELTS (expr));
> hack without and with the following patch on a simple small testcase with
> -O2 -flto.
> Got 574 bytes without the opc-save-gen.awk change and 454 bytes with it,
> that is ~ 21% saving on the TREE_OPTIMIZATION streaming.

OK, not spectacular but I guess good enough.  So I'd say the below
patch using bp_pack_var_len_{int,unsigned} is OK.

Thanks,
Richard.

> 2020-09-14  Jakub Jelinek  <jakub@redhat.com>
> 
> 	* optc-save-gen.awk: In cl_optimization_stream_out use
> 	bp_pack_var_len_{int,unsigned} instead of bp_pack_value.  In
> 	cl_optimization_stream_in use bp_unpack_var_len_{int,unsigned}
> 	instead of bp_unpack_value.  Formatting fix.
> 
> --- gcc/optc-save-gen.awk.jj	2020-09-14 09:04:35.879854156 +0200
> +++ gcc/optc-save-gen.awk	2020-09-14 10:38:47.722424942 +0200
> @@ -1257,8 +1257,10 @@ for (i = 0; i < n_opt_val; i++) {
>  	otype = var_opt_val_type[i];
>  	if (otype ~ "^const char \\**$")
>  		print "  bp_pack_string (ob, bp, ptr->" name", true);";
> +	else if (otype ~ "^unsigned")
> +		print "  bp_pack_var_len_unsigned (bp, ptr->" name");";
>  	else
> -		print "  bp_pack_value (bp, ptr->" name", 64);";
> +		print "  bp_pack_var_len_int (bp, ptr->" name");";
>  }
>  print "  for (size_t i = 0; i < sizeof (ptr->explicit_mask) / sizeof (ptr->explicit_mask[0]); i++)";
>  print "    bp_pack_value (bp, ptr->explicit_mask[i], 64);";
> @@ -1274,14 +1276,15 @@ print "{";
>  for (i = 0; i < n_opt_val; i++) {
>  	name = var_opt_val[i]
>  	otype = var_opt_val_type[i];
> -	if (otype ~ "^const char \\**$")
> -	{
> -	      print "  ptr->" name" = bp_unpack_string (data_in, bp);";
> -	      print "  if (ptr->" name")";
> -	      print "    ptr->" name" = xstrdup (ptr->" name");";
> +	if (otype ~ "^const char \\**$") {
> +		print "  ptr->" name" = bp_unpack_string (data_in, bp);";
> +		print "  if (ptr->" name")";
> +		print "    ptr->" name" = xstrdup (ptr->" name");";
>  	}
> +	else if (otype ~ "^unsigned")
> +		print "  ptr->" name" = (" var_opt_val_type[i] ") bp_unpack_var_len_unsigned (bp);";
>  	else
> -	      print "  ptr->" name" = (" var_opt_val_type[i] ") bp_unpack_value (bp, 64);";
> +		print "  ptr->" name" = (" var_opt_val_type[i] ") bp_unpack_var_len_int (bp);";
>  }
>  print "  for (size_t i = 0; i < sizeof (ptr->explicit_mask) / sizeof (ptr->explicit_mask[0]); i++)";
>  print "    ptr->explicit_mask[i] = bp_unpack_value (bp, 64);";
> 
> 
> 	Jakub
> 
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)