RISC-V: Optimize consecutive permutation index pattern by vrgather.vi/vx

RISC-V: Optimize consecutive permutation index pattern by vrgather.vi/vx

This patch optimize this following permutation with consecutive patterns index:

typedef char vnx16i __attribute__ ((vector_size (16)));

#define MASK_16 12, 13, 14, 15, 12, 13, 14, 15, 12, 13, 14, 15, 12, 13, 14, 15

vnx16i __attribute__ ((noinline, noclone))
test_1 (vnx16i x, vnx16i y)
{
  return __builtin_shufflevector (x, y, MASK_16);
}

Before this patch:

        lui     a5,%hi(.LC0)
        addi    a5,a5,%lo(.LC0)
        vsetivli        zero,16,e8,m1,ta,ma
        vle8.v  v3,0(a5)
        vle8.v  v2,0(a1)
        vrgather.vv     v1,v2,v3
        vse8.v  v1,0(a0)
        ret

After this patch:

	vsetivli	zero,16,e8,mf8,ta,ma
	vle8.v	v2,0(a1)
	vsetivli	zero,4,e32,mf2,ta,ma
	vrgather.vi	v1,v2,3
	vsetivli	zero,16,e8,mf8,ta,ma
	vse8.v	v1,0(a0)
	ret

Overal reduce 1 instruction which is vector load instruction which is much more expansive
than VL toggling.

Also, with this patch, we are using vrgather.vi which reduce 1 vector register consumption.

gcc/ChangeLog:

	* config/riscv/riscv-v.cc (shuffle_consecutive_patterns): New function.
	(expand_vec_perm_const_1): Add consecutive pattern recognition.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/vls/def.h: Add new test.
	* gcc.target/riscv/rvv/autovec/vls-vlmax/consecutive-1.c: New test.
	* gcc.target/riscv/rvv/autovec/vls-vlmax/consecutive-2.c: New test.
	* gcc.target/riscv/rvv/autovec/vls-vlmax/consecutive_run-1.c: New test.
	* gcc.target/riscv/rvv/autovec/vls-vlmax/consecutive_run-2.c: New test.
	* gcc.target/riscv/rvv/autovec/vls/consecutive-1.c: New test.
	* gcc.target/riscv/rvv/autovec/vls/consecutive-2.c: New test.
	* gcc.target/riscv/rvv/autovec/vls/consecutive-3.c: New test.