[Bug rtl-optimization/47521] Unnecessary usage of edx register

[law at redhat dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47521

--- Comment #4 from Jeffrey A. Law <law at redhat dot com> 2011-02-03 13:54:16 UTC ---
I'd hoped it would be possible to define a set of conditions under which
combine could combine the conditional move with the subsequent move into a hard
register.  Without special casing the instruction patterns, reading the
constraints and the like, I doubt that's going to be possible.

The other approach I see is to have copyrename avoid coalescing the temporaries
with "a".  That in turn prevents "a" from being live throughout the entire
function and we get the desired register allocations and code.