[PING] options: Clarify 'Init' option property usage for streaming optimization (was: [PATCH] options, lto: Optimize streaming of optimization nodes)
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Commit Message
Hi!
Ping. For convenience, I've re-attached
"options: Clarify 'Init' option property usage for streaming optimization".
(I've re-verified: "No functional change; no change in generated files.")
Grüße
Thomas
On 2022-03-31T15:22:59+0200, I wrote:
> 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);";
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Comments
On Wed, 26 Oct 2022, Thomas Schwinge wrote:
> Hi!
>
> Ping. For convenience, I've re-attached
> "options: Clarify 'Init' option property usage for streaming optimization".
> (I've re-verified: "No functional change; no change in generated files.")
OK.
From c7968fa44b1073dfa7da3a11470a9e76b6faafaf Mon Sep 17 00:00:00 2001
From: Thomas Schwinge <thomas@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(-)
@@ -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