Hi,
using -fno-semantic-interposition has been reported by various people
to bring about considerable speed up at the cost of strict compliance
to the ELF symbol interposition rules See for example
https://fedoraproject.org/wiki/Changes/PythonNoSemanticInterpositionSpeedup
As such I believe it should be implied by our -Ofast optimization
level, not only so that benchmarks that can benefit run faster, but
also so that people looking at -Ofast documentation for options that
could speed their programs find it.
I have verified that with the following patch IPA-CP sees
flag_semantic_interposition set to zero at Ofast and that info and pdf
manual builds fine with the documentation change. I am bootstrapping
and testing it now in order to comply with submission criteria but I
don't think an Ofast change gets much tested.
Assuming it passes, is the patch OK? (If it is, I will also add a note
about it in the "Caveats" section in gcc-12/changes.html of wwwdocs
after I commit the patch.)
Thanks,
Martin
gcc/ChangeLog:
2021-11-12 Martin Jambor <mjam...@suse.cz>
* opts.c (default_options_table): Switch off
flag_semantic_interposition at Ofast.
* doc/invoke.texi (Optimize Options): Document that Ofast switches off
-fsemantic-interposition.
---
gcc/doc/invoke.texi | 1 +
gcc/opts.c | 1 +
2 files changed, 2 insertions(+)
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 2ea23d07c4c..fd16c91aec8 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -10551,6 +10551,7 @@ valid for all standard-compliant programs.
It turns on @option{-ffast-math}, @option{-fallow-store-data-races}
and the Fortran-specific @option{-fstack-arrays}, unless
@option{-fmax-stack-var-size} is specified, and @option{-fno-protect-parens}.
+It turns off @option {-fsemantic-interposition}.
@item -Og
@opindex Og
diff --git a/gcc/opts.c b/gcc/opts.c
index caed6255500..3da53d8f890 100644
--- a/gcc/opts.c
+++ b/gcc/opts.c
@@ -682,6 +682,7 @@ static const struct default_options default_options_table[]
=
/* -Ofast adds optimizations to -O3. */
{ OPT_LEVELS_FAST, OPT_ffast_math, NULL, 1 },
{ OPT_LEVELS_FAST, OPT_fallow_store_data_races, NULL, 1 },
+ { OPT_LEVELS_FAST, OPT_fsemantic_interposition, NULL, 0 },
{ OPT_LEVELS_NONE, 0, NULL, 0 }
};
--
2.33.0
