* configure.ac: Warn about --enable-link-time-optimization's issues

in --help message.

Fixes: debbugs:17806

diff --git a/ChangeLog b/ChangeLog
index 17d3f9401a39b8f4462bcc151d298dee842d5644..07954be7d6b6caf408246d74cc3ab87813ec0332 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,8 @@
 2014-06-20  Paul Eggert  <eggert@cs.ucla.edu>
 
+       * configure.ac: Warn about --enable-link-time-optimization's issues
+       in --help message (Bug#17806).
+
        Port to GCC 4.9.0 with link time optimization (Bug#17806).
        * configure.ac (CFLAGS): With link time optimization,
        use -ffat-lto-objects if supported; otherwise Emacs won't

diff --git a/configure.ac b/configure.ac
index e9400047edcaaccebc0c03990d547b4f97e38072..3d840a1b48417218887d5a151d0ce3a6b42b5471 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -757,7 +757,10 @@ AC_ARG_ENABLE([gcc-warnings],
 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.])],
+                This requires GCC 4.5.0 or later.
+                It also makes Emacs harder to debug, and when we tried it
+                with GCC 4.9.0 x86-64 it made Emacs slower, so it's not
+                recommended for typical use.])],
 if test "${enableval}" != "no"; then
    AC_MSG_CHECKING([whether link-time optimization is supported])
    ac_lto_supported=no