Re: [Qemu-arm] [PATCH v3 2/5] target/arm: optimize rev16() using extract op

[Richard Henderson]

On 05/12/2017 11:21 AM, Aurelien Jarno wrote:
> +    uint64_t mask1 = sf ? 0x00ff00ff00ff00ffull : 0x00ff00ff;
> +    uint64_t mask2 = sf ? 0xff00ff00ff00ff00ull : 0xff00ff00;
> +
> +    tcg_gen_shri_i64(tcg_tmp, tcg_rn, 8);
> +    tcg_gen_andi_i64(tcg_tmp, tcg_tmp, mask1);
> +    tcg_gen_shli_i64(tcg_rd, tcg_rn, 8);
> +    tcg_gen_andi_i64(tcg_rd, tcg_rd, mask2);

It would probably be better to use a single mask, since they're not free to 
instantiate in a register.  So e.g.

  TCGv mask = tcg_const_i64(sf ? 0x00ff00ff00ff00ffull : 0x00ff00ff);
  tcg_gen_shri_i64(tcg_tmp, tcg_rn, 8);
  tcg_gen_and_i64(tcg_rd, tcg_rn, mask);
  tcg_gen_and_i64(tcg_tmp, tcg_tmp, mask);
  tcg_gen_shli_i64(tcg_rd, tcg_rd, 8);


r~