[Bug rtl-optimization/50427] IRA fails to detect conflict

[bigotp at acm dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50427

--- Comment #1 from Peter A. Bigot <bigotp at acm dot org> 2011-09-16 10:25:31 UTC ---
Created attachment 25302
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=25302
Potential fix for problem

As far as I can tell, IRA misses this because it doesn't detect that the back
end has generated RTL with pre-assigned general-purpose hard registers. 
Whether this technique is valid or not, it is also used in the avr backend for
the same purpose (preparing to call a support routine that does not follow the
standard ABI), though in that case the use is deeper in a parallel insn.

The attached patch appears to fix the problem in my situation.  I'd appreciate
any comments and suggestions if there's a better solution.