The following patch solves the 2nd case of

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61578

   I did a lot of benchmarking of different heuristics in hard reg cost 
propagation in IRA.  This is the best what I found.  The patch improves 
stably code size of SPEC2000 and its score although it is not that 
significant.

   The patch was tested and bootstrapped on x86-64.

   Committed as rev. 228097.

2015-09-24  Vladimir Makarov  <vmakarov@redhat.com>

         PR target/61578
         * ira-color.c (update_allocno_cost): Add parameter.
         (update_costs_from_allocno): Decrease conflict cost.  Pass the new
         parameter.