Re: [PATCH 12/15] Hexagon (target/hexagon) bit reverse (brev) addressing

[Richard Henderson]

On 3/24/21 8:50 PM, Taylor Simpson wrote:
> +static inline void gen_fbrev(TCGv result, TCGv src)
> +{
> +    /*
> +     *  Bit reverse the low 16 bits of the address
> +     */
> +    TCGv tmp = tcg_temp_new();
> +    tcg_gen_andi_tl(result, src, 0xffff0000);
> +    for (int i = 0; i < 16; i++) {
> +        tcg_gen_extract_tl(tmp, src, i, 1);
> +        tcg_gen_deposit_tl(result, result, tmp, 15 - i, 1);
> +    }
> +    tcg_temp_free(tmp);
> +}

This is very sub-optimal.  Coordinate with rev.ng, who added this as well.  But 
even there my suggestion was

uint32_t helper_fbrev(uint32_t x)
{
    return deposit32(x, 0, 16, revbit16(x));
}

because this operation is fairly large in tcg ops.


r~