Use vrsub.vi to subtract from a constant.

Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 tcg/riscv/tcg-target-con-set.h | 1 +
 tcg/riscv/tcg-target.c.inc     | 8 ++++++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/tcg/riscv/tcg-target-con-set.h b/tcg/riscv/tcg-target-con-set.h
index 97e6ecdb0f..d8ce5414f5 100644
--- a/tcg/riscv/tcg-target-con-set.h
+++ b/tcg/riscv/tcg-target-con-set.h
@@ -25,6 +25,7 @@ C_O0_I2(v, r)
 C_O1_I1(v, r)
 C_O1_I1(v, v)
 C_O1_I2(v, v, v)
+C_O1_I2(v, vK, v)
 C_O1_I2(v, v, vK)
 C_O1_I2(v, v, vL)
 C_O1_I4(v, v, vL, vK, vK)
diff --git a/tcg/riscv/tcg-target.c.inc b/tcg/riscv/tcg-target.c.inc
index ce8d6d0293..1ce2f291d3 100644
--- a/tcg/riscv/tcg-target.c.inc
+++ b/tcg/riscv/tcg-target.c.inc
@@ -2350,7 +2350,11 @@ static void tcg_out_vec_op(TCGContext *s, TCGOpcode opc,
         break;
     case INDEX_op_sub_vec:
         set_vtype_len_sew(s, type, vece);
-        tcg_out_opc_vv(s, OPC_VSUB_VV, a0, a1, a2);
+        if (const_args[1]) {
+            tcg_out_opc_vi(s, OPC_VRSUB_VI, a0, a2, a1);
+        } else {
+            tcg_out_opc_vv(s, OPC_VSUB_VV, a0, a1, a2);
+        }
         break;
     case INDEX_op_and_vec:
         set_vtype_len(s, type);
@@ -2565,7 +2569,7 @@ static TCGConstraintSetIndex tcg_target_op_def(TCGOpcode op)
     case INDEX_op_xor_vec:
         return C_O1_I2(v, v, vK);
     case INDEX_op_sub_vec:
-        return C_O1_I2(v, v, v);
+        return C_O1_I2(v, vK, v);
     case INDEX_op_cmp_vec:
         return C_O1_I2(v, v, vL);
     case INDEX_op_cmpsel_vec:
-- 
2.43.0