arm: Auto-vectorization for MVE: vcmp

Since MVE has a different set of vector comparison operators from
Neon, we have to update the expansion to take into account the new
ones, for instance 'NE' for which MVE does not require to use 'EQ'
with the inverted condition.

Conversely, Neon supports comparisons with #0, MVE does not.

For:
typedef long int vs32 __attribute__((vector_size(16)));
vs32 cmp_eq_vs32_reg (vs32 a, vs32 b) { return a == b; }

we now generate:
cmp_eq_vs32_reg:
	vldr.64 d4, .L123       @ 8     [c=8 l=4]  *mve_movv4si/8
	vldr.64 d5, .L123+8
	vldr.64 d6, .L123+16    @ 9     [c=8 l=4]  *mve_movv4si/8
	vldr.64 d7, .L123+24
	vcmp.i32  eq, q0, q1    @ 7     [c=16 l=4]  mve_vcmpeqq_v4si
	vpsel q0, q3, q2        @ 15    [c=8 l=4]  mve_vpselq_sv4si
	bx      lr      @ 26    [c=8 l=4]  *thumb2_return
.L124:
	.align  3
.L123:
	.word   0
	.word   0
	.word   0
	.word   0
	.word   1
	.word   1
	.word   1
	.word   1

For some reason emit_move_insn (zero, CONST0_RTX (cmp_mode)) produces
a pair of vldr instead of vmov.i32, qX, #0

2021-05-17  Christophe Lyon  <christophe.lyon@linaro.org>

	gcc/
	* config/arm/arm-protos.h (arm_expand_vector_compare): Update
	prototype.
	* config/arm/arm.c (arm_expand_vector_compare): Add support for
	MVE.
	(arm_expand_vcond): Likewise.
	* config/arm/iterators.md (supf): Remove VCMPNEQ_S, VCMPEQQ_S,
	VCMPEQQ_N_S, VCMPNEQ_N_S.
	(VCMPNEQ, VCMPEQQ, VCMPEQQ_N, VCMPNEQ_N): Remove.
	* config/arm/mve.md (@mve_vcmp<mve_cmp_op>q_<mode>): Add '@' prefix.
	(@mve_vcmp<mve_cmp_op>q_f<mode>): Likewise.
	(@mve_vcmp<mve_cmp_op>q_n_f<mode>): Likewise.
	(@mve_vpselq_<supf><mode>): Likewise.
	(@mve_vpselq_f<mode>"): Likewise.
	* config/arm/neon.md (vec_cmp<mode><v_cmp_result): Enable for MVE
	and move to vec-common.md.
	(vec_cmpu<mode><mode>): Likewise.
	(vcond<mode><mode>): Likewise.
	(vcond<V_cvtto><mode>): Likewise.
	(vcondu<mode><v_cmp_result>): Likewise.
	(vcond_mask_<mode><v_cmp_result>): Likewise.
	* config/arm/unspecs.md (VCMPNEQ_U, VCMPNEQ_S, VCMPEQQ_S)
	(VCMPEQQ_N_S, VCMPNEQ_N_S, VCMPEQQ_U, CMPEQQ_N_U, VCMPNEQ_N_U)
	(VCMPGEQ_N_S, VCMPGEQ_S, VCMPGTQ_N_S, VCMPGTQ_S, VCMPLEQ_N_S)
	(VCMPLEQ_S, VCMPLTQ_N_S, VCMPLTQ_S, VCMPCSQ_N_U, VCMPCSQ_U)
	(VCMPHIQ_N_U, VCMPHIQ_U): Remove.
	* config/arm/vec-common.md (vec_cmp<mode><v_cmp_result): Moved
	from neon.md.
	(vec_cmpu<mode><mode>): Likewise.
	(vcond<mode><mode>): Likewise.
	(vcond<V_cvtto><mode>): Likewise.
	(vcondu<mode><v_cmp_result>): Likewise.
	(vcond_mask_<mode><v_cmp_result>): Likewise. Added unsafe math
	condition.

	gcc/testsuite
	* gcc.target/arm/simd/mve-compare-1.c: New test with GCC vectors.
	* gcc.target/arm/simd/mve-compare-2.c: New test with GCC vectors.
	* gcc.target/arm/simd/mve-compare-scalar-1.c: New test with GCC
	vectors.
	* gcc.target/arm/simd/mve-vcmp-f32.c: New test for
	auto-vectorization.
	* gcc.target/arm/simd/mve-vcmp.c: New test for auto-vectorization.