Do not zero-extend the input to the cas for subword operations;
instead, use the appropriate zero-extending compare insns.
Correct the predicates and constraints for immediate expected operand.
* config/aarch64/aarch64.c (aarch64_gen_compare_reg_maybe_ze): New.
(aarch64_split_compare_and_swap): Use it.
(aarch64_expand_compare_and_swap): Likewise. Remove convert_modes;
test oldval against the proper predicate.
* config/aarch64/atomics.md (@atomic_compare_and_swap<ALLI>):
Use nonmemory_operand for expected.
(cas_short_expected_pred): New.
(@aarch64_compare_and_swap<SHORT>): Use it; use "rn" not "rI" to match.
(@aarch64_compare_and_swap<GPI>): Use "rn" not "rI" for expected.
* config/aarch64/predicates.md (aarch64_plushi_immediate): New.
(aarch64_plushi_operand): New.
From-SVN: r265657
