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

[Jakub Jelinek <jakub@redhat.com>]

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.

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