Issue #25702: A --with-lto configure option has been added that will
enable link time optimizations at build time during a make profile-opt.
Some compilers and toolchains are known to not produce stable code when
using LTO, be sure to test things thoroughly before relying on it.
It can provide a few % speed up over profile-opt alone.
diff --git a/Makefile.pre.in b/Makefile.pre.in
index 865d754..d54a098 100644
--- a/Makefile.pre.in
+++ b/Makefile.pre.in
@@ -451,7 +451,7 @@
$(MAKE) profile-removal
build_all_generate_profile:
- $(MAKE) all CFLAGS="$(CFLAGS) $(PGO_PROF_GEN_FLAG)" LDFLAGS="$(LDFLAGS) $(PGO_PROF_GEN_FLAG)" LIBS="$(LIBS)"
+ $(MAKE) all CFLAGS="$(CFLAGS) $(PGO_PROF_GEN_FLAG) @LTOFLAGS@" LDFLAGS="$(LDFLAGS) $(PGO_PROF_GEN_FLAG) @LTOFLAGS@" LIBS="$(LIBS)"
run_profile_task:
: # FIXME: can't run for a cross build
@@ -461,7 +461,7 @@
$(LLVM_PROF_MERGER)
build_all_use_profile:
- $(MAKE) all CFLAGS="$(CFLAGS) $(PGO_PROF_USE_FLAG)"
+ $(MAKE) all CFLAGS="$(CFLAGS) $(PGO_PROF_USE_FLAG) @LTOFLAGS@" LDFLAGS="$(LDFLAGS) @LTOFLAGS@"
# Compile and run with gcov
.PHONY=coverage coverage-lcov coverage-report
diff --git a/Misc/NEWS b/Misc/NEWS
index c52b294..309cb62 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,12 @@
Core and Builtins
-----------------
+- Issue #25702: A --with-lto configure option has been added that will
+ enable link time optimizations at build time during a make profile-opt.
+ Some compilers and toolchains are known to not produce stable code when
+ using LTO, be sure to test things thoroughly before relying on it.
+ It can provide a few % speed up over profile-opt alone.
+
- Issue #26168: Fixed possible refleaks in failing Py_BuildValue() with the "N"
format unit.
diff --git a/configure b/configure
index 6abe24d..6b8e37f 100755
--- a/configure
+++ b/configure
@@ -667,6 +667,7 @@
LLVM_PROF_MERGER
PGO_PROF_USE_FLAG
PGO_PROF_GEN_FLAG
+LTOFLAGS
UNIVERSAL_ARCH_FLAGS
BASECFLAGS
OPT
@@ -796,6 +797,7 @@
enable_shared
enable_profiling
with_pydebug
+with_lto
enable_toolbox_glue
with_libs
with_system_expat
@@ -1477,6 +1479,8 @@
compiler
--with-suffix=.exe set executable suffix
--with-pydebug build with Py_DEBUG defined
+ --with-lto Enable Link Time Optimization in PGO builds.
+ Disabled by default.
--with-libs='lib1 ...' link against additional libs
--with-system-expat build pyexpat module using an installed expat
library
@@ -6366,6 +6370,49 @@
fi
+# Enable LTO flags
+
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for --with-lto" >&5
+$as_echo_n "checking for --with-lto... " >&6; }
+
+# Check whether --with-lto was given.
+if test "${with_lto+set}" = set; then :
+ withval=$with_lto;
+if test "$withval" != no
+then
+ Py_LTO='true'
+ { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+$as_echo "yes" >&6; };
+else
+ Py_LTO='false'
+ { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; };
+fi
+else
+ { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
+if test "$Py_LTO" = 'true' ; then
+ case $CC in
+ *clang*)
+ # Any changes made here should be reflected in the GCC+Darwin case below
+ LTOFLAGS="-flto"
+ ;;
+ *gcc*)
+ case $ac_sys_system in
+ Darwin*)
+ LTOFLAGS="-flto"
+ ;;
+ *)
+ LTOFLAGS="-flto -fuse-linker-plugin -ffat-lto-objects -flto-partition=none"
+ ;;
+ esac
+ ;;
+ esac
+fi
+
+
# Enable PGO flags.
diff --git a/configure.ac b/configure.ac
index f0082fd..06c877b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1377,6 +1377,40 @@
fi
+# Enable LTO flags
+AC_SUBST(LTOFLAGS)
+AC_MSG_CHECKING(for --with-lto)
+AC_ARG_WITH(lto, AS_HELP_STRING([--with-lto], [Enable Link Time Optimization in PGO builds. Disabled by default.]),
+[
+if test "$withval" != no
+then
+ Py_LTO='true'
+ AC_MSG_RESULT(yes);
+else
+ Py_LTO='false'
+ AC_MSG_RESULT(no);
+fi],
+[AC_MSG_RESULT(no)])
+if test "$Py_LTO" = 'true' ; then
+ case $CC in
+ *clang*)
+ # Any changes made here should be reflected in the GCC+Darwin case below
+ LTOFLAGS="-flto"
+ ;;
+ *gcc*)
+ case $ac_sys_system in
+ Darwin*)
+ LTOFLAGS="-flto"
+ ;;
+ *)
+ LTOFLAGS="-flto -fuse-linker-plugin -ffat-lto-objects -flto-partition=none"
+ ;;
+ esac
+ ;;
+ esac
+fi
+
+
# Enable PGO flags.
AC_SUBST(PGO_PROF_GEN_FLAG)
AC_SUBST(PGO_PROF_USE_FLAG)