Hi!
On 2020-11-18T10:36:35+0100, Jakub Jelinek via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
> Honza mentioned that especially for the new param machinery, most of
> streamed values are probably going to be the default values. Perhaps
> somehow we could stream them more effectively.
>
> This patch implements it and brings further savings, the size
> goes down from 574 bytes to 273 bytes, i.e. less than half.
Neat idea about the XOR-encoding!
> Not trying to handle enums because the code doesn't know if (enum ...) 10
> is even valid, similarly non-parameters because those really generally
> don't have large initializers, and params without Init (those are 0
> initialized and thus don't need to be handled).
Given this only looks at 'Init', I understand this may actually
mis-optimize in the case that there is an 'Init' present, but that value
is then "by default" overridden via 'LANG_HOOKS_INIT_OPTIONS_STRUCT', or
'TARGET_OPTION_OVERRIDE', for example. (I'm however not claiming that's
an actual problem to be worried about -- just for my understanding.)
Either way:
> * optc-save-gen.awk: Initialize var_opt_init. In
> cl_optimization_stream_out for params with default values larger than
> 10, xor the default value with the actual parameter value. In
> cl_optimization_stream_in repeat the above xor.
> --- gcc/optc-save-gen.awk.jj 2020-09-14 10:51:54.493740942 +0200
> +++ gcc/optc-save-gen.awk 2020-09-14 11:39:39.441602594 +0200
> @@ -1186,6 +1186,7 @@ for (i = 0; i < n_opts; i++) {
> var_opt_val_type[n_opt_val] = otype;
> var_opt_val[n_opt_val] = "x_" name;
> var_opt_hash[n_opt_val] = flag_set_p("Optimization", flags[i]);
> + var_opt_init[n_opt_val] = opt_args("Init", flags[i]);
> n_opt_val++;
> }
> }
Reading through the options handling, I was confused why 'Init' needs to
be handled in 'gcc/optc-save-gen.awk'. To help the next person -- like,
me in a few weeks ;-) -- wondering about this, OK to push the attached
"options: Clarify 'Init' option property usage for streaming
optimization"?
Grüße
Thomas
> @@ -1257,10 +1258,21 @@ 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_var_len_int (bp, ptr->" name");";
> + else {
> + if (otype ~ "^unsigned") {
> + sgn = "unsigned";
> + } else {
> + sgn = "int";
> + }
> + if (name ~ "^x_param" && !(otype ~ "^enum ") &&
> var_opt_init[i]) {
> + print " if (" var_opt_init[i] " > ("
> var_opt_val_type[i] ") 10)";
> + print " bp_pack_var_len_" sgn " (bp, ptr->" name" ^
> " var_opt_init[i] ");";
> + print " else";
> + print " bp_pack_var_len_" sgn " (bp, ptr->" name");";
> + } else {
> + print " bp_pack_var_len_" sgn " (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);";
> @@ -1281,10 +1293,18 @@ for (i = 0; i < n_opt_val; i++) {
> 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_var_len_int (bp);";
> + else {
> + if (otype ~ "^unsigned") {
> + sgn = "unsigned";
> + } else {
> + sgn = "int";
> + }
> + print " ptr->" name" = (" var_opt_val_type[i] ")
> bp_unpack_var_len_" sgn " (bp);";
> + if (name ~ "^x_param" && !(otype ~ "^enum ") &&
> var_opt_init[i]) {
> + print " if (" var_opt_init[i] " > ("
> var_opt_val_type[i] ") 10)";
> + print " ptr->" name" ^= " var_opt_init[i] ";";
> + }
> + }
> }
> 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);";
-----------------
Siemens Electronic Design Automation GmbH; Anschrift: Arnulfstraße 201, 80634
München; Gesellschaft mit beschränkter Haftung; Geschäftsführer: Thomas
Heurung, Frank Thürauf; Sitz der Gesellschaft: München; Registergericht
München, HRB 106955
>From c7968fa44b1073dfa7da3a11470a9e76b6faafaf Mon Sep 17 00:00:00 2001
From: Thomas Schwinge <tho...@codesourcery.com>
Date: Thu, 31 Mar 2022 12:06:29 +0200
Subject: [PATCH] options: Clarify 'Init' option property usage for streaming
optimization
This clarifies commit 95db7e9afe57ca1c269d46baa2accced004e5c74
"options, lto: Optimize streaming of optimization nodes".
No functional change; no change in generated files.
gcc/
* optc-save-gen.awk: Clarify 'Init' option property usage for
streaming optimization.
---
gcc/optc-save-gen.awk | 31 ++++++++++++++++++++++++-------
1 file changed, 24 insertions(+), 7 deletions(-)
diff --git a/gcc/optc-save-gen.awk b/gcc/optc-save-gen.awk
index 9911bab6668..c60b300f693 100644
--- a/gcc/optc-save-gen.awk
+++ b/gcc/optc-save-gen.awk
@@ -1292,7 +1292,22 @@ for (i = 0; i < n_opts; i++) {
var_opt_val_type[n_opt_val] = otype;
var_opt_val[n_opt_val] = "x_" name;
var_opt_hash[n_opt_val] = flag_set_p("Optimization", flags[i]);
- var_opt_init[n_opt_val] = opt_args("Init", flags[i]);
+
+ # If applicable, optimize streaming for the common case that
+ # the current value is unchanged from the 'Init' value:
+ # XOR-encode it so that we stream value zero.
+ # Not handling non-parameters as those really generally don't
+ # have large initializers.
+ # Not handling enums as we don't know if '(enum ...) 10' is
+ # even valid (see synthesized 'if' conditionals below).
+ if (flag_set_p("Param", flags[i]) \
+ && !(otype ~ "^enum ")) {
+ # Those without 'Init' are zero-initialized and thus
+ # already encoded ideally.
+ init = opt_args("Init", flags[i])
+ var_opt_optimize_init[n_opt_val] = init;
+ }
+
n_opt_val++;
}
}
@@ -1370,9 +1385,10 @@ for (i = 0; i < n_opt_val; i++) {
} else {
sgn = "int";
}
- if (name ~ "^x_param" && !(otype ~ "^enum ") && var_opt_init[i]) {
- print " if (" var_opt_init[i] " > (" var_opt_val_type[i] ") 10)";
- print " bp_pack_var_len_" sgn " (bp, ptr->" name" ^ " var_opt_init[i] ");";
+ # If applicable, encode the streamed value.
+ if (var_opt_optimize_init[i]) {
+ print " if (" var_opt_optimize_init[i] " > (" var_opt_val_type[i] ") 10)";
+ print " bp_pack_var_len_" sgn " (bp, ptr->" name" ^ " var_opt_optimize_init[i] ");";
print " else";
print " bp_pack_var_len_" sgn " (bp, ptr->" name");";
} else {
@@ -1406,9 +1422,10 @@ for (i = 0; i < n_opt_val; i++) {
sgn = "int";
}
print " ptr->" name" = (" var_opt_val_type[i] ") bp_unpack_var_len_" sgn " (bp);";
- if (name ~ "^x_param" && !(otype ~ "^enum ") && var_opt_init[i]) {
- print " if (" var_opt_init[i] " > (" var_opt_val_type[i] ") 10)";
- print " ptr->" name" ^= " var_opt_init[i] ";";
+ # If applicable, decode the streamed value.
+ if (var_opt_optimize_init[i]) {
+ print " if (" var_opt_optimize_init[i] " > (" var_opt_val_type[i] ") 10)";
+ print " ptr->" name" ^= " var_opt_optimize_init[i] ";";
}
}
}
--
2.35.1
