[PATCH][v5] RISC-V: add option -m(no-)autovec-segment

[PATCH][v5] RISC-V: add option -m(no-)autovec-segment

Add option -m(no-)autovec-segment to enable/disable autovectorizer
from emitting vector segment load/store instructions. This is useful for
performance experiments.

gcc/ChangeLog:
	* config/riscv/autovec.md (vec_mask_len_load_lanes, vec_mask_len_store_lanes):
	Predicate with TARGET_VECTOR_AUTOVEC_SEGMENT
	* config/riscv/riscv-opts.h (TARGET_VECTOR_AUTOVEC_SEGMENT): New macro.
	* config/riscv/riscv.opt (-m(no-)autovec-segment): New option.

gcc/testsuite/ChangeLog:
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_load_noseg-1.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_load_noseg-2.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_load_noseg-3.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_load_noseg-4.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_load_noseg-5.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_load_noseg-6.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_load_noseg-7.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_load_noseg_run-1.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_load_noseg_run-2.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_load_noseg_run-3.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_load_noseg_run-4.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_load_noseg_run-5.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_load_noseg_run-6.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_load_noseg_run-7.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_store_noseg-1.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_store_noseg-2.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_store_noseg-3.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_store_noseg-4.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_store_noseg-5.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_store_noseg-6.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_store_noseg-7.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_store_noseg_run-1.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_store_noseg_run-2.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_store_noseg_run-3.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_store_noseg_run-4.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_store_noseg_run-5.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_store_noseg_run-6.c:
	New test.
	* gcc.target/riscv/rvv/autovec/struct/mask_struct_store_noseg_run-7.c:
	New test.
	* gcc.target/riscv/rvv/autovec/no-segment.c: New test.