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.

1 files changed, 47 insertions, 0 deletions

diff --git a/configure b/configure
index 6abe24dff8..6b8e37f0d2 100755
--- a/configure
+++ b/configure
@@ -667,6 +667,7 @@ LLVM_PROF_FILE
 LLVM_PROF_MERGER
 PGO_PROF_USE_FLAG
 PGO_PROF_GEN_FLAG
+LTOFLAGS
 UNIVERSAL_ARCH_FLAGS
 BASECFLAGS
 OPT
@@ -796,6 +797,7 @@ with_suffix
 enable_shared
 enable_profiling
 with_pydebug
+with_lto
 enable_toolbox_glue
 with_libs
 with_system_expat
@@ -1477,6 +1479,8 @@ Optional Packages:
                           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 @@ rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 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.