arm: Implement auto-vectorized MVE comparisons with vectors of boolean predicates

We make use of qualifier_predicate to describe MVE builtins
prototypes, restricting to auto-vectorizable vcmp* and vpsel builtins,
as they are exercised by the tests added earlier in the series.

Special handling is needed for mve_vpselq because it has a v2di
variant, which has no natural VPR.P0 representation: we keep HImode
for it.

The vector_compare expansion code is updated to use the right VxBI
mode instead of HI for the result.

We extend the existing thumb2_movhi_vfp and thumb2_movhi_fp16 patterns
to use the new MVE_7_HI iterator which covers HI and the new VxBI
modes, in conjunction with the new DB constraint for a constant vector
of booleans.

This patch also adds tests derived from the one provided in PR
target/101325: there is a compile-only test because I did not have
access to anything that could execute MVE code until recently.  I have
been able to add an executable test since QEMU supports MVE.

Instead of adding arm_v8_1m_mve_hw, I update arm_mve_hw so that it
uses add_options_for_arm_v8_1m_mve_fp, like arm_neon_hw does.  This
ensures arm_mve_hw passes even if the toolchain does not generate MVE
code by default.

Most of the work of this patch series was carried out while I was
working at STMicroelectronics as a Linaro assignee.

2022-02-22  Christophe Lyon <christophe.lyon@arm.com>
	    Richard Sandiford  <richard.sandiford@arm.com>

	gcc/
	PR target/100757
	PR target/101325
	* config/arm/arm-builtins.cc (BINOP_PRED_UNONE_UNONE_QUALIFIERS)
	(BINOP_PRED_NONE_NONE_QUALIFIERS)
	(TERNOP_NONE_NONE_NONE_PRED_QUALIFIERS)
	(TERNOP_UNONE_UNONE_UNONE_PRED_QUALIFIERS): New.
	* config/arm/arm-protos.h (mve_bool_vec_to_const): New.
	* config/arm/arm.cc (arm_hard_regno_mode_ok): Handle new VxBI
	modes.
	(arm_mode_to_pred_mode): New.
	(arm_expand_vector_compare): Use the right VxBI mode instead of
	HI.
	(arm_expand_vcond): Likewise.
	(simd_valid_immediate): Handle MODE_VECTOR_BOOL.
	(mve_bool_vec_to_const): New.
	(neon_make_constant): Call mve_bool_vec_to_const when needed.
	* config/arm/arm_mve_builtins.def (vcmpneq_, vcmphiq_, vcmpcsq_)
	(vcmpltq_, vcmpleq_, vcmpgtq_, vcmpgeq_, vcmpeqq_, vcmpneq_f)
	(vcmpltq_f, vcmpleq_f, vcmpgtq_f, vcmpgeq_f, vcmpeqq_f, vpselq_u)
	(vpselq_s, vpselq_f): Use new predicated qualifiers.
	* config/arm/constraints.md (DB): New.
	* config/arm/iterators.md (MVE_7, MVE_7_HI): New mode iterators.
	(MVE_VPRED, MVE_vpred): New attribute iterators.
	* config/arm/mve.md (@mve_vcmp<mve_cmp_op>q_<mode>)
	(@mve_vcmp<mve_cmp_op>q_f<mode>, @mve_vpselq_<supf><mode>)
	(@mve_vpselq_f<mode>): Use MVE_VPRED instead of HI.
	(@mve_vpselq_<supf>v2di): Define separately.
	(mov<mode>): New expander for VxBI modes.
	* config/arm/vfp.md (thumb2_movhi_vfp, thumb2_movhi_fp16): Use
	MVE_7_HI iterator and add support for DB constraint.

	gcc/testsuite/
	PR target/100757
	PR target/101325
	* gcc.dg/rtl/arm/mve-vxbi.c: New test.
	* gcc.target/arm/simd/pr101325.c: New.
	* gcc.target/arm/simd/pr101325-2.c: New.
	* lib/target-supports.exp (check_effective_target_arm_mve_hw): Use
	add_options_for_arm_v8_1m_mve_fp.

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