* 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).