[AArch64] Handle more SVE predicate constants

[AArch64] Handle more SVE predicate constants

This patch handles more predicate constants by using TRN1, TRN2
and EOR.  For now, only one operation is allowed before we fall
back to loading from memory or doing an integer move and a compare.
The EOR support includes the important special case of an inverted
predicate.

The real motivating case for this is the ACLE svdupq function,
which allows a repeating 16-bit predicate to be built from
individual scalar booleans.  It's not easy to test properly
before that support is merged.

2019-08-14  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* config/aarch64/aarch64.c (aarch64_expand_sve_const_pred_eor)
	(aarch64_expand_sve_const_pred_trn): New functions.
	(aarch64_expand_sve_const_pred_1): Add a recurse_p parameter and
	use the above functions when the parameter is true.
	(aarch64_expand_sve_const_pred): Update call accordingly.
	* config/aarch64/aarch64-sve.md (*aarch64_sve_<perm_insn><mode>):
	Rename to...
	(@aarch64_sve_<perm_insn><mode>): ...this.

gcc/testsuite/
	* gcc.target/aarch64/sve/peel_ind_1.c: Look for an inverted .B VL1.
	* gcc.target/aarch64/sve/peel_ind_2.c: Likewise .S VL7.

From-SVN: r274434