* configure.ac (--enable-link-time-optimization): Add clang support.

* INSTALL: Mention it.
* etc/PROBLEMS: Mention potential problems with
--enable-link-time-optimization and clang on Fedora 20.

5 files changed, 80 insertions, 33 deletions

diff --git a/ChangeLog b/ChangeLog
index c66f6b726f5..c4ee59eb844 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2014-05-13  Dmitry Antipov  <dmantipov@yandex.ru>
+
+	* configure.ac (--enable-link-time-optimization): Add clang support.
+	* INSTALL: Mention it.
+
 2014-05-12  Katsumi Yamaoka  <yamaoka@jpl.org>
 
 	* configure.ac (EMACS_CHECK_MODULES): Fix typo in previous change.
diff --git a/INSTALL b/INSTALL
index 496c6c8c376..3502631cbcf 100644
--- a/INSTALL
+++ b/INSTALL
@@ -331,12 +331,17 @@ and is useful with GNU-compatible compilers.  On a recent GNU system
 there should be no warnings; on older and on non-GNU systems the
 generated warnings may still be useful.
 
-Use --enable-link-time-optimization to enable link-time optimizer, which
-is available in GNU compiler since version 4.5.0.  If your compiler is not
-GNU or older than version 4.5.0, this option does nothing.  If `configure'
-can determine number of online CPUS on your system, final link-time
-optimization and code generation is executed in parallel using one job
-per each available online CPU.
+Use --enable-link-time-optimization to enable link-time optimizer.  If
+you're using GNU compiler, this feature is supported since version 4.5.0.
+If `configure' can determine number of online CPUS on your system, final
+link-time optimization and code generation is executed in parallel using
+one job per each available online CPU.
+
+This option is also supported for clang.  You should have GNU binutils
+with `gold' linker and plugin support, and clang with LLVMgold.so plugin.
+Read http://llvm.org/docs/GoldPlugin.html for details.  Also note that
+this feature is still experimental, so prepare to build binutils and
+clang from the corresponding source code repositories.
 
 The `--prefix=PREFIXDIR' option specifies where the installation process
 should put emacs and its data files.  This defaults to `/usr/local'.
diff --git a/configure.ac b/configure.ac
index a0d6abc4b1a..b2ce64adeb7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -762,32 +762,6 @@ AC_ARG_ENABLE([gcc-warnings],
   [gl_gcc_warnings=no]
 )
 
-AC_ARG_ENABLE(link-time-optimization,
-[AS_HELP_STRING([--enable-link-time-optimization],
-                [build emacs with link-time optimization.
-                 This is supported only for GCC since 4.5.0.])],
-if test "${enableval}" != "no"; then
-   AC_MSG_CHECKING([whether link-time optimization is supported])
-   ac_lto_supported=no
-   if test x$GCC = xyes; then
-      CPUS=`getconf _NPROCESSORS_ONLN 2>/dev/null`
-      if test x$CPUS != x; then
-      	 LTO="-flto=$CPUS"
-      else
-	 LTO="-flto"
-      fi
-      old_CFLAGS=$CFLAGS
-      CFLAGS="$CFLAGS $LTO"
-      AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]], [[]])],
-      	[ac_lto_supported=yes], [ac_lto_supported=no])
-      CFLAGS="$old_CFLAGS"
-   fi
-   AC_MSG_RESULT([$ac_lto_supported])
-   if test "$ac_lto_supported" = "yes"; then
-      CFLAGS="$CFLAGS $LTO"
-   fi
-fi)
-
 # clang is unduly picky about some things.
 AC_CACHE_CHECK([whether the compiler is clang], [emacs_cv_clang],
   [AC_COMPILE_IFELSE(
@@ -913,7 +887,51 @@ edit_cflags="
   s/^ //
 "
 
-
+AC_ARG_ENABLE(link-time-optimization,
+[AS_HELP_STRING([--enable-link-time-optimization],
+                [build emacs with link-time optimization.
+		 This is supported for gcc since 4.5.0 and clang.
+		 Note that clang support is experimental - see INSTALL])],
+if test "${enableval}" != "no"; then
+   ac_lto_supported=no
+   if test $emacs_cv_clang = yes; then
+      AC_MSG_CHECKING([whether link-time optimization is supported by clang])
+      GOLD_PLUGIN=`$CC -print-file-name=LLVMgold.so 2>/dev/null`
+      if test -x "$GOLD_PLUGIN"; then
+	 LTO="-flto"
+      fi
+   elif test x$GCC = xyes; then
+      AC_MSG_CHECKING([whether link-time optimization is supported by gcc])
+      CPUS=`getconf _NPROCESSORS_ONLN 2>/dev/null`
+      if test x$CPUS != x; then
+	 LTO="-flto=$CPUS"
+      else
+	 LTO="-flto"
+      fi
+   else
+      AC_MSG_ERROR([Link-time optimization is not supported with your compiler.])
+   fi
+   if test -z "$LTO"; then
+      ac_lto_supported=no
+   else
+      old_CFLAGS=$CFLAGS
+      CFLAGS="$CFLAGS $LTO"
+      AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]], [[]])],
+         [ac_lto_supported=yes], [ac_lto_supported=no])
+         CFLAGS="$old_CFLAGS"
+   fi
+   AC_MSG_RESULT([$ac_lto_supported])
+   if test "$ac_lto_supported" = "yes"; then
+      CFLAGS="$CFLAGS $LTO"
+      if test x$emacs_cv_clang = xyes; then
+	 AC_MSG_WARN([Please read INSTALL before using link-time optimization with clang])
+	 # WARNING: 'ar --plugin ...' doesn't work without
+	 # command, so plugin name is appended to ARFLAGS.
+	 ARFLAGS="cru --plugin $GOLD_PLUGIN"
+	 RANLIB="$RANLIB --plugin $GOLD_PLUGIN"
+      fi
+   fi
+fi)
 
 dnl Some other nice autoconf tests.
 dnl These are commented out, since gl_EARLY and/or Autoconf already does them.
diff --git a/etc/ChangeLog b/etc/ChangeLog
index 3eb1c564fad..ea0db240725 100644
--- a/etc/ChangeLog
+++ b/etc/ChangeLog
@@ -1,3 +1,8 @@
+2014-05-13  Dmitry Antipov  <dmantipov@yandex.ru>
+
+	* PROBLEMS: Mention potential problems with
+	--enable-link-time-optimization and clang on Fedora 20.
+
 2014-05-04  Leo Liu  <sdl.web@gmail.com>
 
 	* NEWS: Mention support for Chinese dates in calendar and diary.
diff --git a/etc/PROBLEMS b/etc/PROBLEMS
index cf025ce4b9e..6ea699384f1 100644
--- a/etc/PROBLEMS
+++ b/etc/PROBLEMS
@@ -836,6 +836,20 @@ you want to use fcitx with Emacs, you have two choices.  Toggle fcitx
 by another key (e.g. C-\) by modifying ~/.fcitx/config, or be
 accustomed to use C-@ for `set-mark-command'.
 
+*** Link-time optimization with clang doesn't work on Fedora 20.
+
+As of May 2014, Fedora 20 has broken LLVMgold.so plugin support in clang
+(tested with clang-3.4-6.fc20) - `clang --print-file-name=LLVMgold.so'
+prints `LLVMgold.so' instead of full path to plugin shared library, and
+`clang -flto' is unable to find the plugin with the following error:
+
+/bin/ld: error: /usr/bin/../lib/LLVMgold.so: could not load plugin library:
+/usr/bin/../lib/LLVMgold.so: cannot open shared object file: No such file
+or directory
+
+The only way to avoid this is to build your own clang from source code
+repositories, as described at http://clang.llvm.org/get_started.html.
+
 *** M-SPC seems to be ignored as input.
 
 See if your X server is set up to use this as a command