[AArch64] Rework SVE integer comparisons

[AArch64] Rework SVE integer comparisons

The remaining uses of UNSPEC_MERGE_PTRUE were in integer comparison
patterns.  These aren't actually merging operations but zeroing ones,
although there's no practical difference when the predicate is a PTRUE.

All comparisons produced by expand are predicated on a PTRUE,
although we try to pattern-match a compare-and-AND as a predicated
comparison during combine.

Like previous patches, this one rearranges things in a way that works
better with the ACLE, where the initial predicate might or might not
be a PTRUE.  The new patterns use UNSPEC_PRED_Z to represent zeroing
predication, with a aarch64_sve_ptrue_flag to record whether the
predicate is all-true (as for UNSPEC_PTEST).

See the block comment in the patch for more details.

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

gcc/
	* config/aarch64/aarch64-protos.h (aarch64_sve_same_pred_for_ptest_p):
	Declare.
	* config/aarch64/aarch64.c (aarch64_sve_same_pred_for_ptest_p)
	(aarch64_sve_emit_int_cmp): New functions.
	(aarch64_convert_sve_data_to_pred): Use aarch64_sve_emit_int_cmp.
	(aarch64_sve_cmp_operand_p, aarch64_emit_sve_ptrue_op_cc): Delete.
	(aarch64_expand_sve_vec_cmp_int): Use aarch64_sve_emit_int_cmp.
	* config/aarch64/aarch64.md (UNSPEC_MERGE_PTRUE): Delete.
	(UNSPEC_PRED_Z): New unspec.
	(set_clobber_cc_nzc): Delete.
	* config/aarch64/aarch64-sve.md: Add a block comment about
	UNSPEC_PRED_Z.
	(*cmp<SVE_INT_CMP:cmp_op><mode>): Rename to...
	(@aarch64_pred_cmp<SVE_INT_CMP:cmp_op><mode>): ...this, replacing
	the old pattern with that name.  Use UNSPEC_PRED_Z instead of
	UNSPEC_MERGE_PTRUE.
	(*cmp<SVE_INT_CMP:cmp_op><mode>_cc): Use UNSPEC_PRED_Z instead of
	UNSPEC_MERGE_PTRUE.  Use aarch64_sve_same_pred_for_ptest_p to
	check for compatible predicates.
	(*cmp<cmp_op><SVE_INT_CMP:mode>_ptest): Likewise.
	(*cmp<cmp_op><mode>_and): Match a known-ptrue UNSPEC_PRED_Z instead
	of UNSPEC_MERGE_PTRUE.  Split into the new form of predicated
	comparisons above.

From-SVN: r274429