The following patch solves a problem reported for MIPS by Richard 
Sandiford in

http://gcc.gnu.org/ml/gcc/2008-09/msg00484.html

Richard reported that it solves some worst problems:

http://gcc.gnu.org/ml/gcc/2008-10/msg00268.html

The patch was successfully tested and bootstrapped on x86_64.

Is it ok to commit the patch to the trunk?

2008-10-14  Vladimir Makarov  <vmakarov@redhat.com>

   * ira-int.h (ira_allocno): Add member updated_cover_class_cost.
   (ALLOCNO_UPDATED_COVER_CLASS_COST): New.
   (ira_fast_allocation): Remove the prototype.
  
   * ira-color.c (update_copy_costs, allocno_cost_compare_func,
   assign_hard_reg, calculate_allocno_spill_cost): Use updated costs.
   (color_pass): Modify the updated costs.
   (ira_color): Rename to color.  Make it static.
   (ira_fast_allocation): Rename to fast_allocation.  Make it static.
   (ira_color): New function.
  
   * ira-conflicts.c (process_regs_for_copy): Propagate hard reg cost
   change.

   * ira-lives.c (last_call_num, allocno_saved_at_call): New
   variables.
   (set_allocno_live, clear_allocno_live, mark_ref_live,
   mark_ref_dead): Invalidate corresponding element of
   allocno_saved_at_call.
   (process_bb_node_lives): Increment last_call_num.  Setup
   allocno_saved_at_call.  Don't increase ALLOCNO_CALL_FREQ if the
   allocno was already saved.
   (ira_create_allocno_live_ranges): Initiate last_call_num and
   allocno_saved_at_call.

   * ira-build.c (ira_create_allocno): Initiate
   ALLOCNO_UPDATED_COVER_CLASS_COST.
   (create_cap_allocno, propagate_allocno_info,
   remove_unnecessary_allocnos): Remove setting updated costs.
   (ira_flattening): Set up ALLOCNO_UPDATED_COVER_CLASS_COST.

   * ira.c (ira):  Don't call ira_fast_allocation.

   * ira-costs.c (setup_allocno_cover_class_and_costs): Don't set up
   updated costs.