On Tue, Aug 18, 2020 at 4:36 PM Jonathan Wakely via Gcc-patches <gcc-patches@gcc.gnu.org> wrote: > > On 17/08/20 18:15 +0000, Aditya K via Libstdc++ wrote: > >This would help compiler optimize local static objects. > > > >Added changelog. > > Please don't :-) > > GCC patch policies always said NOT to change the ChangeLog in the > patch, because the ChangeLog files change so rapidly that it means by > the time you've sent the patch, it no longer applies. > > Current GCC policies are that NOBODY changes the ChangeLog files, they > are autogenerated from Git commit logs once per day. > > So please just include the proposed ChangeLog entry as the Git commit > message in the body of your email. > > Patch for libstdc++ need to go to both the libstdc++ list and the > gcc-patches list, in the same email. Not sent once to each list as > separate emails. > > > > >``` > >From c6cba40e0434147db89d3af05b598782cde651e3 Mon Sep 17 00:00:00 2001 > >From: Aditya Kumar <1894981+hiradi...@users.noreply.github.com> > >Date: Thu, 13 Aug 2020 09:41:34 -0700 > >Subject: [PATCH] Add cold attribute to one time construction APIs > > > >__cxa_guard_acquire is used for only one purpose, > >namely guarding local static variable initialization, > >and since that purpose is definitionally cold, it should be attributed as > >cold. > > Definitionally isn't a word. Attributed is a word, but it doesn't mean > marked with an attribute. > > >Similarly for __cxa_guard_release and __cxa_guard_abort > >--- > > libstdc++-v3/ChangeLog | 5 +++++ > > libstdc++-v3/include/bits/c++config | 5 +++++ > > libstdc++-v3/libsupc++/cxxabi.h | 6 +++--- > > 3 files changed, 13 insertions(+), 3 deletions(-) > > > >diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog > >index fe6884bf3..86b707ac7 100644 > >--- a/libstdc++-v3/ChangeLog > >+++ b/libstdc++-v3/ChangeLog > >@@ -1,3 +1,8 @@ > >+2020-08-17 Aditya Kumar <hiradi...@msn.com> > >+ * libstdc++-v3/include/bits/c++config: Add _GLIBCXX_NOTHROW attribute > >+ * libstdc++-v3/libsupc++/cxxabi.h (__cxa_guard_acquire, > >__cxa_guard_release, > >+ __cxa_guard_abort): Add _GLIBCXX_NOTHROW attribute. > > The changelog format is wrong. There should be a blank line after the > date+author line, and you're adding _GLIBCXX_COLD not > _GLIBCXX_NOTHROW. But it shouldn't be here at all as explained above. > > > 2020-08-14 Lewis Hyatt <lhy...@gmail.com> > > > > * testsuite/lib/libstdc++.exp: Use the new option > >diff --git a/libstdc++-v3/include/bits/c++config > >b/libstdc++-v3/include/bits/c++config > >index b1fad59d4..f6f954eef 100644 > >--- a/libstdc++-v3/include/bits/c++config > >+++ b/libstdc++-v3/include/bits/c++config > >@@ -42,6 +42,7 @@ > > // _GLIBCXX_NORETURN > > // _GLIBCXX_NOTHROW > > // _GLIBCXX_VISIBILITY > >+// _GLIBCXX_COLD > > #ifndef _GLIBCXX_PURE > > # define _GLIBCXX_PURE __attribute__ ((__pure__)) > > #endif > >@@ -74,6 +75,10 @@ > > # define _GLIBCXX_VISIBILITY(V) _GLIBCXX_PSEUDO_VISIBILITY(V) > > #endif > > > >+#ifndef _GLIBCXX_COLD > >+# define _GLIBCXX_COLD __attribute__ ((cold)) > >+#endif > > "cold" is not a reserved name so this needs to be __cold__. > > I'm not sure we really need it in <bits/c++config.h> if we only use it > in one file, but maybe we'll find more uses for it later. > > >diff --git a/libstdc++-v3/libsupc++/cxxabi.h > >b/libstdc++-v3/libsupc++/cxxabi.h > >index 000713ecd..24c1366e2 100644 > >--- a/libstdc++-v3/libsupc++/cxxabi.h > >+++ b/libstdc++-v3/libsupc++/cxxabi.h > >@@ -115,13 +115,13 @@ namespace __cxxabiv1 > > void (*__dealloc) (void*, size_t)); > > > > int > >- __cxa_guard_acquire(__guard*); > >+ __cxa_guard_acquire(__guard*) _GLIBCXX_COLD; > > The GCC manual says that functions marked cold will be optimized for > size not for speed. Is that really what we want here? > > It makes sense to put them in a cold section, but I think we still > want them to be optimized for speed, don't we? > > I've attached a patch addressing the issues above, but I'd like to > know whether the change to how the functions are optimized is > desirable, or even noticable.
Hmm, but the functions are always executed? The .cold sections are so they are not paged in and this particular case would defeat this purpose? Richard. >
