RISC-V: RISC-V: Support gather_load/scatter RVV auto-vectorization

This patch fully support gather_load/scatter_store:
1. Support single-rgroup on both RV32/RV64.
2. Support indexed element width can be same as or smaller than Pmode.
3. Support VLA SLP with gather/scatter.
4. Fully tested all gather/scatter with LMUL = M1/M2/M4/M8 both VLA and VLS.
5. Fix bug of handling (subreg:SI (const_poly_int:DI))
6. Fix bug on vec_perm which is used by gather/scatter SLP.

All kinds of GATHER/SCATTER are normalized into LEN_MASK_*.
We fully supported these 4 kinds of gather/scatter:
1. LEN_MASK_GATHER_LOAD/LEN_MASK_SCATTER_STORE with dummy length and dummy mask (Full vector).
2. LEN_MASK_GATHER_LOAD/LEN_MASK_SCATTER_STORE with dummy length and real mask.
3. LEN_MASK_GATHER_LOAD/LEN_MASK_SCATTER_STORE with real length and dummy mask.
4. LEN_MASK_GATHER_LOAD/LEN_MASK_SCATTER_STORE with real length and real mask.

Base on the disscussions with Richards, we don't lower vlse/vsse in RISC-V backend for strided load/store.
Instead, we leave it to the middle-end to handle that.

Regression is pass ok for trunk ?

gcc/ChangeLog:

	* config/riscv/autovec.md
	(len_mask_gather_load<VNX1_QHSD:mode><VNX1_QHSDI:mode>): New pattern.
	(len_mask_gather_load<VNX2_QHSD:mode><VNX2_QHSDI:mode>): Ditto.
	(len_mask_gather_load<VNX4_QHSD:mode><VNX4_QHSDI:mode>): Ditto.
	(len_mask_gather_load<VNX8_QHSD:mode><VNX8_QHSDI:mode>): Ditto.
	(len_mask_gather_load<VNX16_QHSD:mode><VNX16_QHSDI:mode>): Ditto.
	(len_mask_gather_load<VNX32_QHS:mode><VNX32_QHSI:mode>): Ditto.
	(len_mask_gather_load<VNX64_QH:mode><VNX64_QHI:mode>): Ditto.
	(len_mask_gather_load<mode><mode>): Ditto.
	(len_mask_scatter_store<VNX1_QHSD:mode><VNX1_QHSDI:mode>): Ditto.
	(len_mask_scatter_store<VNX2_QHSD:mode><VNX2_QHSDI:mode>): Ditto.
	(len_mask_scatter_store<VNX4_QHSD:mode><VNX4_QHSDI:mode>): Ditto.
	(len_mask_scatter_store<VNX8_QHSD:mode><VNX8_QHSDI:mode>): Ditto.
	(len_mask_scatter_store<VNX16_QHSD:mode><VNX16_QHSDI:mode>): Ditto.
	(len_mask_scatter_store<VNX32_QHS:mode><VNX32_QHSI:mode>): Ditto.
	(len_mask_scatter_store<VNX64_QH:mode><VNX64_QHI:mode>): Ditto.
	(len_mask_scatter_store<mode><mode>): Ditto.
	* config/riscv/predicates.md (const_1_operand): New predicate.
	(vector_gs_scale_operand_16): Ditto.
	(vector_gs_scale_operand_32): Ditto.
	(vector_gs_scale_operand_64): Ditto.
	(vector_gs_extension_operand): Ditto.
	(vector_gs_scale_operand_16_rv32): Ditto.
	(vector_gs_scale_operand_32_rv32): Ditto.
	* config/riscv/riscv-protos.h (enum insn_type): Add gather/scatter.
	(expand_gather_scatter): New function.
	* config/riscv/riscv-v.cc (gen_const_vector_dup): Add gather/scatter.
	(emit_vlmax_masked_store_insn): New function.
	(emit_nonvlmax_masked_store_insn): Ditto.
	(modulo_sel_indices): Ditto.
	(expand_vec_perm): Fix SLP for gather/scatter.
	(prepare_gather_scatter): New function.
	(expand_gather_scatter): Ditto.
	* config/riscv/riscv.cc (riscv_legitimize_move): Fix bug of
	(subreg:SI (DI CONST_POLY_INT)).
	* config/riscv/vector-iterators.md: Add gather/scatter.
	* config/riscv/vector.md (vec_duplicate<mode>): Use "@" instead.
	(@vec_duplicate<mode>): Ditto.
	(@pred_indexed_<order>store<VNX16_QHS:mode><VNX16_QHSDI:mode>):
	Fix name.
	(@pred_indexed_<order>store<VNX16_QHSD:mode><VNX16_QHSDI:mode>): Ditto.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/rvv.exp: Add gather/scatter tests.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load-1.c: New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load-10.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load-11.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load-12.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load-2.c: New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load-3.c: New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load-4.c: New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load-5.c: New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load-6.c: New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load-7.c: New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load-8.c: New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load-9.c: New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load_run-1.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load_run-10.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load_run-11.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load_run-12.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load_run-2.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load_run-3.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load_run-4.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load_run-5.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load_run-6.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load_run-7.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load_run-8.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/gather_load_run-9.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_gather_load-1.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_gather_load-10.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_gather_load-11.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_gather_load-2.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_gather_load-3.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_gather_load-4.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_gather_load-5.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_gather_load-6.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_gather_load-7.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_gather_load-8.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_gather_load-9.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_gather_load_run-1.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_gather_load_run-10.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_gather_load_run-11.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_gather_load_run-2.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_gather_load_run-3.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_gather_load_run-4.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_gather_load_run-5.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_gather_load_run-6.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_gather_load_run-7.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_gather_load_run-8.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_gather_load_run-9.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_scatter_store-1.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_scatter_store-10.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_scatter_store-2.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_scatter_store-3.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_scatter_store-4.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_scatter_store-5.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_scatter_store-6.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_scatter_store-7.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_scatter_store-8.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_scatter_store-9.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_scatter_store_run-1.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_scatter_store_run-10.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_scatter_store_run-2.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_scatter_store_run-3.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_scatter_store_run-4.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_scatter_store_run-5.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_scatter_store_run-6.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_scatter_store_run-7.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_scatter_store_run-8.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/mask_scatter_store_run-9.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/scatter_store-1.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/scatter_store-10.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/scatter_store-2.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/scatter_store-3.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/scatter_store-4.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/scatter_store-5.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/scatter_store-6.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/scatter_store-7.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/scatter_store-8.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/scatter_store-9.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/scatter_store_run-1.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/scatter_store_run-10.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/scatter_store_run-2.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/scatter_store_run-3.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/scatter_store_run-4.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/scatter_store_run-5.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/scatter_store_run-6.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/scatter_store_run-7.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/scatter_store_run-8.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/scatter_store_run-9.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/strided_load-1.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/strided_load-2.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/strided_load_run-1.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/strided_load_run-2.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/strided_store-1.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/strided_store-2.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/strided_store_run-1.c:
	New test.
	* gcc.target/riscv/rvv/autovec/gather-scatter/strided_store_run-2.c:
	New test.