Re: [Qemu-devel] [PATCH 09/35] target/mips: Add nanoMIPS 48bit instructions

[Richard Henderson]

On 06/20/2018 05:05 AM, Yongbok Kim wrote:
>      case NM_P48I:
> +        insn = cpu_lduw_code(env, ctx->base.pc_next + 4);

Surely split this case out to a new function.  And properly form the common,
signed 32-bit offset once before the switch.

> +        switch ((ctx->opcode >> 16) & 0x1f) {
> +        case NM_LI48:
> +            if (rt != 0) {
> +                tcg_gen_movi_tl(cpu_gpr[rt],
> +                                extract32(ctx->opcode, 0, 16) | insn << 16);

The 32-bit constant is to be sign-extended for nanomips 64.

> +            }
> +            break;
> +        case NM_ADDIU48:
> +            if (rt != 0) {
> +                tcg_gen_addi_tl(cpu_gpr[rt], cpu_gpr[rt],
> +                                extract32(ctx->opcode, 0, 16) | insn << 16);

Likewise.

> +                tcg_gen_ext32s_tl(cpu_gpr[rt], cpu_gpr[rt]);
> +            }
> +            break;
> +        case NM_ADDIUGP48:
> +            if (rt != 0) {
> +                tcg_gen_addi_tl(cpu_gpr[rt], cpu_gpr[28],
> +                                extract32(ctx->opcode, 0, 16) | insn << 16);

Likewise.

> +                tcg_gen_ext32s_tl(cpu_gpr[rt], cpu_gpr[rt]);

Behaves-like DADDIU[GP48].  Which would indicate using gen_op_addr_add[i].

I know you're only targeting nanomips32 now, but I think you need to be clearer
about all of these 64-bit edge cases now, lest they be very difficult to pick
out later.

> +            }
> +            break;
> +        case NM_ADDIUPC48:
> +            if (rt != 0) {
> +                int32_t offset = extract32(ctx->opcode, 0, 16) | insn << 16;
> +                target_long addr = addr_add(ctx, ctx->base.pc_next + 6, 
> offset);
> +
> +                tcg_gen_movi_tl(cpu_gpr[rt], addr);
> +                tcg_gen_ext32s_tl(cpu_gpr[rt], cpu_gpr[rt]);

Likewise.  And the ext32s would be doubly redundant with that already done in
addr_add.


r~