Re: [PATCH v7 09/14] target/riscv: Add orc.b instruction for Zbb, removing gorc/gorci

[Richard Henderson]

On 8/30/21 4:15 AM, Philipp Tomsich wrote:
> +    TCGv  tmp = tcg_temp_new();
> +
> +    /* Set msb in each byte if the byte was zero. */
> +    tcg_gen_subi_tl(tmp, source1, dup_const(MO_8, 0x01));
> +    tcg_gen_andc_tl(tmp, tmp, source1);
> +    tcg_gen_andi_tl(tmp, tmp, dup_const(MO_8, 0x80));
> +
> +    /* Replicate the msb of each byte across the byte. */
> +    tcg_gen_shri_tl(tmp, tmp, 7);
> +    tcg_gen_muli_tl(tmp, tmp, 0xff);
> +
> +    /* Negate */
> +    tcg_gen_not_tl(ret, tmp);

It just occurred to me that we can swap the shift/andi and re-use the same constant, and 
we can fold in the negate with andc.

    TCGv ones = tcg_constant_tl(dup_const(MO_8, 1));
    TCGv tmp = tcg_temp_new();

    tcg_gen_sub_tl(tmp, src1, ones);
    tcg_gen_andc_tl(tmp, tmp, src1);
    tcg_gen_shri_tl(tmp, tmp, 7);
    tcg_gen_andc_tl(tmp, ones, tmp);
    tcg_gen_muli_tl(tmp, tmp, 0xff);

    tcg_temp_free(tmp);


r~