RFA: patch fixing PR37948

[Jeff Law]

Vladimir Makarov wrote:
>  The following patch solves PR37948.  The analysis of the problem can 
> be found
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37948
>
> The patch also switches on extended coalescing in IRA which can be 
> used also for solving the problem.
>
> I found some pitfalls in coalescing code (usage of allocnos itself 
> instead of head of coalescing allocnos list) and fixed that.
>
> The patch was successfully bootstrapped and tested on x86/x86_64.
>
> 2008-11-07  Vladimir Makarov  <vmakarov@redhat.com>
>          PR rtl-optimizations/37948
>    * ira-int.h (struct ira_allocno_copy): New member constraint_p.
>    (ira_create_copy, ira_add_allocno_copy): New parameter.
>
>    * ira-conflicts.c (process_regs_for_copy): New parameter.  Pass it
>    to ira_add_allocno_copy.
>    (process_reg_shuffles, add_insn_allocno_copies): Pass a new
>    parameter to process_regs_for_copy.
>    (propagate_copies): Pass a new parameter to ira_add_allocno_copy.
>    Fix typo in passing second allocno to ira_add_allocno_copy.
>
>    * ira-color.c (update_conflict_hard_regno_costs): Use head of
>    coalesced allocnos list.
>    (assign_hard_reg): Ditto.  Check that assigned allocnos are not in
>    the graph.
>    (add_ira_allocno_to_bucket): Rename to add_allocno_to_bucket.
>    (add_ira_allocno_to_ordered_bucket): Rename to
>    add_allocno_to_ordered_bucket.
>    (push_ira_allocno_to_stack): Rename to push_allocno_to_stack.  Use
>    head of coalesced allocnos list.
>    (push_allocnos_to_stack): Remove calculation of ALLOCNO_TEMP.
>    Check that it is aready calculated.
>    (push_ira_allocno_to_spill): Rename to push_ira_allocno_to_spill.
>    (setup_allocno_left_conflicts_num): Use head of coalesced allocnos
>    list.
>    (coalesce_allocnos): Do extended coalescing too.
>
>    * ira-emit.c (add_range_and_copies_from_move_list): Pass a new
>    parameter to ira_add_allocno_copy.
>
>    * ira-build.c (ira_create_copy, ira_add_allocno_copy): Add a new
>    parameter.
>    (print_copy): Print copy origination too.
>
>    * ira-costs.c (scan_one_insn): Use alloc_pref for load from
>    equivalent memory.
>  
So presumably after these changes your opinion is that extended 
coalescing no longer generates worse code?

Do we need both the extended coalescing and cost change (scan_one_insn) 
to address the performance regression?

The patch is OK -- I'm just trying to make sure the interaction between 
the two hunks is understood and recorded if there are future issues.

Jeff