* loop.c: (PREFETCH_EXTREME_DIFFERENCE, PREFETCH_BEFORE_LOOP): New.
	(PREFETCH_CONDITIONAL): Renamed from PREFETCH_NOT_ALWAYS.
	(struct prefetch_info): Fix spelling of member bytes_accessed.
	(emit_prefetch_instructions): Make dump messages more regular;
	restructure code to add more dump messages; use new macros for
	heuristics. (There are no code generation changes in any of this).

From-SVN: r53371