[AArch64] Rework SVE REV[BHW] patterns

[AArch64] Rework SVE REV[BHW] patterns

The current SVE REV patterns follow the AArch64 scheme, in which
UNSPEC_REV<NN> reverses elements within an <NN>-bit granule.
E.g. UNSPEC_REV64 on VNx8HI reverses the four 16-bit elements
within each 64-bit granule.

The native SVE scheme is the other way around: UNSPEC_REV64 is seen
as an operation on 64-bit elements, with REVB swapping bytes within
the elements, REVH swapping halfwords, and so on.  This fits SVE more
naturally because the operation can then be predicated per <NN>-bit
granule/element.

Making the patterns use the Advanced SIMD scheme was more natural
when all we cared about were permutes, since we could then use
the source and target of the permute in their original modes.
However, the ACLE does need patterns that follow the native scheme,
treating them as operations on integer elements.  This patch defines
the patterns that way instead and updates the existing uses to match.

This also brings in a couple of helper routines from the ACLE branch.

2019-08-15  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* config/aarch64/iterators.md (UNSPEC_REVB, UNSPEC_REVH)
	(UNSPEC_REVW): New constants.
	(elem_bits): New mode attribute.
	(SVE_INT_UNARY): New int iterator.
	(optab): Handle UNSPEC_REV[BHW].
	(sve_int_op): New int attribute.
	(min_elem_bits): Handle VNx16QI and the predicate modes.
	* config/aarch64/aarch64-sve.md (*aarch64_sve_rev64<mode>)
	(*aarch64_sve_rev32<mode>, *aarch64_sve_rev16vnx16qi): Delete.
	(@aarch64_pred_<SVE_INT_UNARY:optab><SVE_I:mode>): New pattern.
	* config/aarch64/aarch64.c (aarch64_sve_data_mode): New function.
	(aarch64_sve_int_mode, aarch64_sve_rev_unspec): Likewise.
	(aarch64_split_sve_subreg_move): Use UNSPEC_REV[BHW] instead of
	unspecs based on the total width of the reversed data.
	(aarch64_evpc_rev_local): Likewise (for SVE only).  Use a
	reinterpret followed by a subreg on big-endian targets.

gcc/testsuite/
	* gcc.target/aarch64/sve/revb_1.c: Restrict to little-endian targets.
	Avoid including stdint.h.
	* gcc.target/aarch64/sve/revh_1.c: Likewise.
	* gcc.target/aarch64/sve/revw_1.c: Likewise.
	* gcc.target/aarch64/sve/revb_2.c: New big-endian test.
	* gcc.target/aarch64/sve/revh_2.c: Likewise.
	* gcc.target/aarch64/sve/revw_2.c: Likewise.

From-SVN: r274517