This patch adds optabs that check whether a read followed by a write
or a write followed by a read can be divided into interleaved byte
accesses without changing the dependencies between the bytes.
This is one of the uses of the SVE2 WHILERW and WHILEWR instructions.
(The instructions can also be used to limit the VF at runtime,
but that's future work.)

2019-11-18  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* doc/sourcebuild.texi (vect_check_ptrs): Document.
	* optabs.def (check_raw_ptrs_optab, check_war_ptrs_optab): New optabs.
	* doc/md.texi: Document them.
	* internal-fn.def (IFN_CHECK_RAW_PTRS, IFN_CHECK_WAR_PTRS): New
	internal functions.
	* internal-fn.h (internal_check_ptrs_fn_supported_p): Declare.
	* internal-fn.c (check_ptrs_direct): New macro.
	(expand_check_ptrs_optab_fn): Likewise.
	(direct_check_ptrs_optab_supported_p): Likewise.
	(internal_check_ptrs_fn_supported_p): New fuction.
	* tree-data-ref.c: Include internal-fn.h.
	(create_ifn_alias_checks): New function.
	(create_intersect_range_checks): Use it.
	* config/aarch64/iterators.md (SVE2_WHILE_PTR): New int iterator.
	(optab, cmp_op): Handle it.
	(raw_war, unspec): New int attributes.
	* config/aarch64/aarch64.md (UNSPEC_WHILERW, UNSPEC_WHILE_WR): New
	constants.
	* config/aarch64/predicates.md (aarch64_bytes_per_sve_vector_operand):
	New predicate.
	* config/aarch64/aarch64-sve2.md (check_<raw_war>_ptrs<mode>): New
	expander.
	(@aarch64_sve2_while<cmp_op><GPI:mode><PRED_ALL:mode>_ptest): New
	pattern.

gcc/testsuite/
	* lib/target-supports.exp (check_effective_target_vect_check_ptrs):
	New procedure.
	* gcc.dg/vect/vect-alias-check-14.c: Expect IFN_CHECK_WAR to be
	used, if available.
	* gcc.dg/vect/vect-alias-check-15.c: Likewise.
	* gcc.dg/vect/vect-alias-check-16.c: Likewise IFN_CHECK_RAW.
	* gcc.target/aarch64/sve2/whilerw_1.c: New test.
	* gcc.target/aarch64/sve2/whilewr_1.c: Likewise.
	* gcc.target/aarch64/sve2/whilewr_2.c: Likewise.

From-SVN: r278414