[Bug target/60480] gcc 4.8.2 fails to do optimization on global register variables when compiling on x86_64 Linux.

[ganboing at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60480

--- Comment #2 from ganboing at gmail dot com ---
(In reply to Andrew Pinski from comment #1)
> This is due to x86 being a small register class target.

The thing is that x86_64 has 16 GPRs, and register r12-r15 are preserved across
function calls (SYSV ABI x86_64). The should be no reason that such opt. can't
be done.