Add MVT::i16s type?

Hi,
I have a special hardware, it have two different ALU units, use different registers. It’s hard for DAGIsel to map i32 ISD::ADD to different ALU because LLVM does not aware register class’s differ.

def 16rr : ABCInstALU0rr<funct4, 0b0, OPC_ALU0,
(outs GPR_OUT:$vx), (ins GPR:$rs1, GPR:$rs2),
!strconcat(opcodestr,".S16"), “$rs1, $rs2, $vx”,
[(set i16:$vx, (OpNode i16:$rs1, i16:$rs2))]>;

def 16rr : ABCInstALU1rr<funct4, 0b0, OPC_ALU1,
(outs SGPR16:$vx), (ins SGPR16:$rs1, SGPR16:$rs2),
!strconcat(opcodestr,".S16"), “$rs1, $rs2, $vx”,
[(set i16:$vx, (OpNode i16:$rs1, i16:$rs2))]>;

5 for(i=0; i<loopNum; i++ )
6 a[i+offset] = b;
line 5: i++ have to run on ALU0

line 6: i+offset have to run on ALU1

It’s hard for me to add context analysis during DAG because that is function scope analysis and also hard to change reigster class(Is there any API for register class update? ).

So I think maybe I should introduce MVT::i16s type and add a pass just before creating SDNode to complete context analysis and update MVT type to solve this issue. What’s your suggestion?