re PR tree-optimization/64058 (Performance degradation after r216304)

re PR tree-optimization/64058 (Performance degradation after r216304)

	PR tree-optimization/64058
	* tree-ssa-coalesce.c (struct coalesce_pair): Add new field INDEX.
	(num_coalesce_pairs): Move up earlier in file.
	(find_coalesce_pair): Initialize the INDEX field for each pair
	discovered.
	(compare_pairs): No longer sort on the elements in each pair.
	Instead break ties with the index of the coalesce pair.

From-SVN: r234149