RISC-V: Combine vec_duplicate + vaaddu.vv to vaaddu.vx on GR2VR cost for HI, QI and...

RISC-V: Combine vec_duplicate + vaaddu.vv to vaaddu.vx on GR2VR cost for HI, QI and SI mode

This patch would like to combine the vec_duplicate + vaaddu.vv to the
vaaddu.vx.  From example as below code.  The related pattern will depend
on the cost of vec_duplicate from GR2VR.  Then the late-combine will
take action if the cost of GR2VR is zero, and reject the combination
if the GR2VR cost is greater than zero.

Assume we have example code like below, GR2VR cost is 0.

  #define DEF_AVG_FLOOR(NT, WT)        \
  NT                                   \
  test_##NT##_avg_floor(NT x, NT y)    \
  {                                    \
    return (NT)(((WT)x + (WT)y) >> 1); \
  }

  #define AVG_FLOOR_FUNC(T)      test_##T##_avg_floor

  DEF_AVG_FLOOR(uint32_t, uint64_t)
  DEF_VX_BINARY_CASE_2_WRAP(T, AVG_FLOOR_FUNC(T), sat_add)

Before this patch:
  11   │     beq a3,zero,.L8
  12   │     vsetvli a5,zero,e32,m1,ta,ma
  13   │     vmv.v.x v2,a2
  14   │     slli    a3,a3,32
  15   │     srli    a3,a3,32
  16   │ .L3:
  17   │     vsetvli a5,a3,e32,m1,ta,ma
  18   │     vle32.v v1,0(a1)
  19   │     slli    a4,a5,2
  20   │     sub a3,a3,a5
  21   │     add a1,a1,a4
  22   │     vaaddu.vv v1,v1,v2
  23   │     vse32.v v1,0(a0)
  24   │     add a0,a0,a4
  25   │     bne a3,zero,.L3

After this patch:
  11   │     beq a3,zero,.L8
  12   │     slli    a3,a3,32
  13   │     srli    a3,a3,32
  14   │ .L3:
  15   │     vsetvli a5,a3,e32,m1,ta,ma
  16   │     vle32.v v1,0(a1)
  17   │     slli    a4,a5,2
  18   │     sub a3,a3,a5
  19   │     add a1,a1,a4
  20   │     vaaddu.vx v1,v1,a2
  21   │     vse32.v v1,0(a0)
  22   │     add a0,a0,a4
  23   │     bne a3,zero,.L3

gcc/ChangeLog:

	* config/riscv/autovec-opt.md (*uavg_floor_vx_<mode>): Add
	pattern for vaaddu.vx combine.
	* config/riscv/riscv.cc (get_vector_binary_rtx_cost): Add UNSPEC
	handling for UNSPEC_VAADDU.
	(riscv_rtx_costs): Ditto.

Signed-off-by: Pan Li <pan2.li@intel.com>