[ARC] Add 'uncached' attribute.

[ARC] Add 'uncached' attribute.

The _Uncached type qualifier can be used to bypass the cache without
resorting to declaring variables as volatile.

gcc/
2018-01-31  Claudiu Zissulescu  <claziss@synopsys.com>

	* config/arc/arc-protos.h (arc_is_uncached_mem_p): Function proto.
	* config/arc/arc.c (arc_handle_uncached_attribute): New function.
	(arc_attribute_table): Add 'uncached' attribute.
	(arc_print_operand): Print '.di' flag for uncached memory
	accesses.
	(arc_in_small_data_p): Do not consider for small data the uncached
	types.
	(arc_is_uncached_mem_p): New function.
	* config/arc/predicates.md (compact_store_memory_operand): Check
	for uncached memory accesses.
	(nonvol_nonimm_operand): Likewise.
	* gcc/doc/extend.texi (ARC Type Attribute): New subsection.

gcc/testsuite
2018-01-31  Claudiu Zissulescu  <claziss@synopsys.com>

	* gcc.target/arc/uncached.c: New test.

From-SVN: r257222