On RISC-V, several C2 instructions can use more accurate ins_pipe, eg.:
```
instruct regI_not_reg(iRegINoSp dst, iRegI src1, immI_M1 m1) %{
  match(Set dst (XorI src1 m1));
  ins_cost(ALU_COST);
  format %{ "xori $dst, $src1, -1\t#@regI_not_reg" %}

  ins_encode %{
    __ xori(as_Register($dst$$reg), as_Register($src1$$reg), -1);
  %}

  ins_pipe(ialu_reg);
%}
```

We can use the more accurate pipe_class `ialu_reg_imm` instead of `ialu_reg`.