=== modified file 'INSTALL'
--- INSTALL	2014-03-27 19:41:57 +0000
+++ INSTALL	2014-04-01 16:08:38 +0000
@@ -331,12 +331,17 @@
 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 snapshots from their source code repositories.
 
 The `--prefix=PREFIXDIR' option specifies where the installation process
 should put emacs and its data files.  This defaults to `/usr/local'.

=== modified file 'configure.ac'
--- configure.ac	2014-03-31 05:02:08 +0000
+++ configure.ac	2014-04-01 16:07:34 +0000
@@ -764,32 +764,6 @@
   [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)
-
 # gl_GCC_VERSION_IFELSE([major], [minor], [run-if-found], [run-if-not-found])
 # ------------------------------------------------
 # If $CPP is gcc-MAJOR.MINOR or newer, then run RUN-IF-FOUND.
@@ -926,7 +900,48 @@
   AC_SUBST([GNULIB_WARN_CFLAGS])
 fi
 
-
+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.
+		 For the latter, this 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`
+      if test -n "$GOLD_PLUGIN" -a -x "$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=$CPUS"
+      else
+	 LTO="-flto"
+      fi
+   else
+      AC_MSG_ERROR([Link-time optimization is not supported with your compiler.])
+   fi
+   old_CFLAGS=$CFLAGS
+   CFLAGS="$CFLAGS $LTO"
+   AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]], [[]])],
+      [ac_lto_supported=yes], [ac_lto_supported=no])
+      CFLAGS="$old_CFLAGS"
+   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 $GOLD_PLUGIN"
+	 # ...but this is much better for ranlib.
+	 RANLIB="$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.