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gh-130048: Reintroduce full LTO as default on Clang (GH-130049)

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Ken Jin 2025-02-13 22:06:00 +08:00 • committed by GitHub
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5 changed files with 14 additions and 102 deletions
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3
Doc/using/configure.rst
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@ -575,6 +575,9 @@ also be used to improve performance.
.. versionchanged:: 3.12
Use ThinLTO as the default optimization policy on Clang if the compiler accepts the flag.
.. versionchanged:: next
Revert to using full LTO as the default optimization policy on Clang.
.. option:: --enable-bolt
Enable usage of the `BOLT post-link binary optimizer

4
Doc/whatsnew/3.14.rst
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@ -1279,6 +1279,10 @@ Build changes
* GNU Autoconf 2.72 is now required to generate :file:`configure`.
(Contributed by Erlend Aasland in :gh:`115765`.)
* CPython now uses Full LTO as the default link time optimization policy
on Clang. This reverts an earlier change in CPython 3.12.
(Contributed by Ken Jin in :gh:`130049`.)
.. _whatsnew314-pep761:
PEP 761: Discontinuation of PGP signatures

1
Misc/NEWS.d/next/Build/2025-02-12-19-51-19.gh-issue-130048.kHNkzP.rst Normal file
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@ -0,0 +1 @@
CPython now uses Full LTO as the default link time optimization policy on Clang. This reverts an earlier change in CPython 3.12.

94
configure generated vendored
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@ -8766,55 +8766,8 @@ printf "%s\n" "$as_me: llvm-ar found via xcrun: ${LLVM_AR}" >&6;}
# Any changes made here should be reflected in the GCC+Darwin case below
if test $Py_LTO_POLICY = default
then
# Check that ThinLTO is accepted.
{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether C compiler accepts -flto=thin" >&5
printf %s "checking whether C compiler accepts -flto=thin... " >&6; }
if test ${ax_cv_check_cflags___flto_thin+y}
then :
printf %s "(cached) " >&6
else case e in #(
e)
ax_check_save_flags=$CFLAGS
CFLAGS="$CFLAGS -flto=thin"
cat confdefs.h - <<_ACEOF >conftest.$ac_ext
/* end confdefs.h. */
int
main (void)
{
;
return 0;
}
_ACEOF
if ac_fn_c_try_compile "$LINENO"
then :
ax_cv_check_cflags___flto_thin=yes
else case e in #(
e) ax_cv_check_cflags___flto_thin=no ;;
esac
fi
rm -f core conftest.err conftest.$ac_objext conftest.beam conftest.$ac_ext
CFLAGS=$ax_check_save_flags ;;
esac
fi
{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $ax_cv_check_cflags___flto_thin" >&5
printf "%s\n" "$ax_cv_check_cflags___flto_thin" >&6; }
if test "x$ax_cv_check_cflags___flto_thin" = xyes
then :
LTOFLAGS="-flto=thin -Wl,-export_dynamic -Wl,-object_path_lto,\"\$@\".lto"
LTOCFLAGS="-flto=thin"
else case e in #(
e)
LTOFLAGS="-flto -Wl,-export_dynamic -Wl,-object_path_lto,\"\$@\".lto"
LTOCFLAGS="-flto"
;;
esac
fi
LTOFLAGS="-flto -Wl,-export_dynamic -Wl,-object_path_lto,\"\$@\".lto"
LTOCFLAGS="-flto"
else
LTOFLAGS="-flto=${Py_LTO_POLICY} -Wl,-export_dynamic -Wl,-object_path_lto,\"\$@\".lto"
LTOCFLAGS="-flto=${Py_LTO_POLICY}"
@ -8823,48 +8776,7 @@ fi
*)
if test $Py_LTO_POLICY = default
then
# Check that ThinLTO is accepted
{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether C compiler accepts -flto=thin" >&5
printf %s "checking whether C compiler accepts -flto=thin... " >&6; }
if test ${ax_cv_check_cflags___flto_thin+y}
then :
printf %s "(cached) " >&6
else case e in #(
e)
ax_check_save_flags=$CFLAGS
CFLAGS="$CFLAGS -flto=thin"
cat confdefs.h - <<_ACEOF >conftest.$ac_ext
/* end confdefs.h. */
int
main (void)
{
;
return 0;
}
_ACEOF
if ac_fn_c_try_compile "$LINENO"
then :
ax_cv_check_cflags___flto_thin=yes
else case e in #(
e) ax_cv_check_cflags___flto_thin=no ;;
esac
fi
rm -f core conftest.err conftest.$ac_objext conftest.beam conftest.$ac_ext
CFLAGS=$ax_check_save_flags ;;
esac
fi
{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $ax_cv_check_cflags___flto_thin" >&5
printf "%s\n" "$ax_cv_check_cflags___flto_thin" >&6; }
if test "x$ax_cv_check_cflags___flto_thin" = xyes
then :
LTOFLAGS="-flto=thin"
else case e in #(
e) LTOFLAGS="-flto" ;;
esac
fi
LTOFLAGS="-flto"
else
LTOFLAGS="-flto=${Py_LTO_POLICY}"
fi

14
configure.ac
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@ -1986,15 +1986,8 @@ if test "$Py_LTO" = 'true' ; then
# Any changes made here should be reflected in the GCC+Darwin case below
if test $Py_LTO_POLICY = default
then
# Check that ThinLTO is accepted.
AX_CHECK_COMPILE_FLAG([-flto=thin],[
LTOFLAGS="-flto=thin -Wl,-export_dynamic -Wl,-object_path_lto,\"\$@\".lto"
LTOCFLAGS="-flto=thin"
],[
LTOFLAGS="-flto -Wl,-export_dynamic -Wl,-object_path_lto,\"\$@\".lto"
LTOCFLAGS="-flto"
]
)
LTOFLAGS="-flto -Wl,-export_dynamic -Wl,-object_path_lto,\"\$@\".lto"
LTOCFLAGS="-flto"
else
LTOFLAGS="-flto=${Py_LTO_POLICY} -Wl,-export_dynamic -Wl,-object_path_lto,\"\$@\".lto"
LTOCFLAGS="-flto=${Py_LTO_POLICY}"
@ -2003,8 +1996,7 @@ if test "$Py_LTO" = 'true' ; then
*)
if test $Py_LTO_POLICY = default
then
# Check that ThinLTO is accepted
AX_CHECK_COMPILE_FLAG([-flto=thin],[LTOFLAGS="-flto=thin"],[LTOFLAGS="-flto"])
LTOFLAGS="-flto"
else
LTOFLAGS="-flto=${Py_LTO_POLICY}"
fi