re PR tree-optimization/64058 (Performance degradation after r216304)
PR tree-optimization/64058
* tree-ssa-coalesce.c (struct coalesce_pair): Add new field
CONFLICT_COUNT.
(struct ssa_conflicts): Move up earlier in the file.
(conflicts_, var_map_): New static variables.
(initialize_conflict_count): New function to initialize the
CONFLICT_COUNT field for each conflict pair.
(compare_pairs): Lazily initialize the conflict count and use it
as the first tie-breaker.
(sort_coalesce_list): Add new arguments conflicts, map. Initialize
and wipe conflicts_ and map_ around the call to qsort. Remove
special case for 2 coalesce pairs.
* bitmap.c (bitmap_count_unique_bits): New function.
(bitmap_count_bits_in_word): New function, extracted from
bitmap_count_bits.
(bitmap_count_bits): Use bitmap_count_bits_in_word.
* bitmap.h (bitmap_count_unique_bits): Declare it.