Clarify what --enable-optimizations does (GH-1847)

configure

@@ -783,7 +783,6 @@ infodir
 docdir
 oldincludedir
 includedir
-runstatedir
 localstatedir
 sharedstatedir
 sysconfdir
@@ -895,7 +894,6 @@ datadir='${datarootdir}'
 sysconfdir='${prefix}/etc'
 sharedstatedir='${prefix}/com'
 localstatedir='${prefix}/var'
-runstatedir='${localstatedir}/run'
 includedir='${prefix}/include'
 oldincludedir='/usr/include'
 docdir='${datarootdir}/doc/${PACKAGE_TARNAME}'
@@ -1148,15 +1146,6 @@ do
   | -silent | --silent | --silen | --sile | --sil)
     silent=yes ;;
 
-  -runstatedir | --runstatedir | --runstatedi | --runstated \
-  | --runstate | --runstat | --runsta | --runst | --runs \
-  | --run | --ru | --r)
-    ac_prev=runstatedir ;;
-  -runstatedir=* | --runstatedir=* | --runstatedi=* | --runstated=* \
-  | --runstate=* | --runstat=* | --runsta=* | --runst=* | --runs=* \
-  | --run=* | --ru=* | --r=*)
-    runstatedir=$ac_optarg ;;
-
   -sbindir | --sbindir | --sbindi | --sbind | --sbin | --sbi | --sb)
     ac_prev=sbindir ;;
   -sbindir=* | --sbindir=* | --sbindi=* | --sbind=* | --sbin=* \
@@ -1294,7 +1283,7 @@ fi
 for ac_var in	exec_prefix prefix bindir sbindir libexecdir datarootdir \
 		datadir sysconfdir sharedstatedir localstatedir includedir \
 		oldincludedir docdir infodir htmldir dvidir pdfdir psdir \
-		libdir localedir mandir runstatedir
+		libdir localedir mandir
 do
   eval ac_val=\$$ac_var
   # Remove trailing slashes.
@@ -1447,7 +1436,6 @@ Fine tuning of the installation directories:
   --sysconfdir=DIR        read-only single-machine data [PREFIX/etc]
   --sharedstatedir=DIR    modifiable architecture-independent data [PREFIX/com]
   --localstatedir=DIR     modifiable single-machine data [PREFIX/var]
-  --runstatedir=DIR       modifiable per-process data [LOCALSTATEDIR/run]
   --libdir=DIR            object code libraries [EPREFIX/lib]
   --includedir=DIR        C header files [PREFIX/include]
   --oldincludedir=DIR     C header files for non-gcc [/usr/include]
@@ -1488,8 +1476,8 @@ Optional Features:
                           Build (MacOSX|Darwin) framework
   --enable-shared         disable/enable building shared python library
   --enable-profiling      enable C-level code profiling
-  --enable-optimizations  Enable expensive optimizations (PGO, etc). Disabled
+  --enable-optimizations  Enable expensive, stable optimizations (PGO, etc).
-                          by default.
+                          Disabled by default.
   --enable-loadable-sqlite-extensions
                           support loadable extensions in _sqlite module
   --enable-ipv6           Enable ipv6 (with ipv4) support
@@ -17989,7 +17977,7 @@ mv config.c Modules
 if test "$Py_OPT" = 'false' -a "$Py_DEBUG" != 'true'; then
     echo "" >&6
     echo "" >&6
-    echo "If you want a release build with all optimizations active (LTO, PGO, etc)," >&6
+    echo "If you want a release build with all stable optimizations active (PGO, etc)," >&6
     echo "please run ./configure --enable-optimizations" >&6
     echo "" >&6
     echo "" >&6

configure.ac

@@ -1277,7 +1277,7 @@ AC_SUBST(DEF_MAKE_ALL_RULE)
 AC_SUBST(DEF_MAKE_RULE)
 Py_OPT='false'
 AC_MSG_CHECKING(for --enable-optimizations)
-AC_ARG_ENABLE(optimizations, AS_HELP_STRING([--enable-optimizations], [Enable expensive optimizations (PGO, etc).  Disabled by default.]),
+AC_ARG_ENABLE(optimizations, AS_HELP_STRING([--enable-optimizations], [Enable expensive, stable optimizations (PGO, etc).  Disabled by default.]),
 [
 if test "$enableval" != no
 then
@@ -5469,7 +5469,7 @@ mv config.c Modules
 if test "$Py_OPT" = 'false' -a "$Py_DEBUG" != 'true'; then
     echo "" >&AS_MESSAGE_FD
     echo "" >&AS_MESSAGE_FD
-    echo "If you want a release build with all optimizations active (LTO, PGO, etc)," >&AS_MESSAGE_FD
+    echo "If you want a release build with all stable optimizations active (PGO, etc)," >&AS_MESSAGE_FD
     echo "please run ./configure --enable-optimizations" >&AS_MESSAGE_FD
     echo "" >&AS_MESSAGE_FD
     echo "" >&AS_MESSAGE_FD