Re: [Qemu-devel] [PATCH 1/3] target-m68k: add abcd/sbcd/nbcd

[Richard Henderson]

On 10/31/2016 03:20 AM, Laurent Vivier wrote:
> +    tcg_gen_subi_i32(addr_src, addr_src, opsize_bytes(OS_BYTE));
> +    src = gen_load(s, OS_BYTE, addr_src, 0);
> +
> +    addr_dest = tcg_temp_new();
> +    if (REG(insn, 0) == REG(insn, 9)) {
> +        tcg_gen_mov_i32(addr_dest, addr_src);
> +    } else {
> +        tcg_gen_mov_i32(addr_dest, AREG(insn, 9));
> +    }
> +    tcg_gen_subi_i32(addr_dest, addr_dest, opsize_bytes(OS_BYTE));
> +    dest = gen_load(s, OS_BYTE, addr_dest, 0);

Write backs before loads.


> +    bcd_neg(tmp, src);
> +    bcd_add(tmp, dest);

Didn't we simplify the subtraction algorithm to make neg?  Why not un-simplify 
it and let nbcd provide a zero (and then let the tcg optimizer do what it can).


r~