Forwarding downstream bug: <https://bugs.gentoo.org/show_bug.cgi?id=358177>

Emacs 23.3 compiled with -O2 on x86_64-pc-linux-gnu immediately fails
with a segmentation fault at runtime. This is with GCC 4.5.2 (but it
also fails when compiled with GCC 4.4.5 or 4.3.5).

   $ emacs -Q
   Fatal error (11)Segmentation fault

The problem disappears when -fno-strict-aliasing is added to CFLAGS.

I've narrowed it down further:
- compile src/xterm.c with -O1,
  compile the rest of the sources with -O2
  => Success
- compile src/xterm.c with -O2,
  compile the rest of the sources with -O1
  => Failure
- compile src/xterm.c with -O2 -fno-strict-aliasing,
  compile the rest of the sources with -O2
  => Success
- compile src/xterm.c with -O1 -fgcse -fstrict-aliasing,
  compile the rest of the sources with -O1
  => Failure

GDB full backtrace is attached.


In GNU Emacs 23.3.1 (x86_64-pc-linux-gnu, X toolkit)
 of 2011-03-10 on juno
Windowing system distributor `The X.Org Foundation', version 11.0.10904000
configured using `configure  '--prefix=/usr' '--build=x86_64-pc-linux-gnu' '--host=x86_64-pc-linux-gnu' '--mandir=/usr/share/man' '--infodir=/usr/share/info' '--datadir=/usr/share' '--sysconfdir=/etc' '--localstatedir=/var/lib' '--libdir=/usr/lib64' '--program-suffix=-emacs-23' '--infodir=/usr/share/info/emacs-23' '--with-crt-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.5.2/../../../../lib64' '--with-gameuser=games' '--without-hesiod' '--without-kerberos' '--without-kerberos5' '--with-gpm' '--with-dbus' '--with-sound' '--with-x' '--without-ns' '--without-gconf' '--without-toolkit-scroll-bars' '--with-gif' '--with-jpeg' '--with-png' '--with-rsvg' '--with-tiff' '--with-xpm' '--with-xft' '--without-libotf' '--without-m17n-flt' '--with-x-toolkit=athena' 'build_alias=x86_64-pc-linux-gnu' 'host_alias=x86_64-pc-linux-gnu' 'CC=gcc' 'CFLAGS=-march=core2 -ggdb -O2 -pipe' 'LDFLAGS=-Wl,-O1 -Wl,--as-needed' 'CPPFLAGS=''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US.utf8
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t