Re: [PATCH v4 04/47] target/ppc: vmulh* instructions without helpers

[Richard Henderson]

On 2/22/22 04:36, matheus.ferst@eldorado.org.br wrote:
> From: "Lucas Mateus Castro (alqotel)" <lucas.castro@eldorado.org.br>
>
> Changed vmulhuw, vmulhud, vmulhsw, vmulhsd to not
> use helpers.
>
> Signed-off-by: Lucas Mateus Castro (alqotel) <lucas.araujo@eldorado.org.br>
> Signed-off-by: Matheus Ferst <matheus.ferst@eldorado.org.br>
> ---
> Changes in v4:
> Changed from gvec to i64, this resulted in a better performance on
> a Power host for all 4 instructions and a better performance for
> vmulhsw and vmulhuw in x86, but a worse performance for vmulhsd and
> vmulhud in a x86 host.

Unsurprising.

> +static void do_vx_vmulhd_i64(TCGv_i64 t, TCGv_i64 a, TCGv_i64 b, bool sign)
> +{
> +    TCGv_i64 a1, b1, mask, w, k;
> +    void (*tcg_gen_shift_imm)(TCGv_i64, TCGv_i64, int64_t);
> +
> +    a1 = tcg_temp_new_i64();
> +    b1 = tcg_temp_new_i64();
> +    w  = tcg_temp_new_i64();
> +    k  = tcg_temp_new_i64();
> +    mask = tcg_temp_new_i64();
> +    if (sign) {
> +        tcg_gen_shift_imm = tcg_gen_sari_i64;
> +    } else {
> +        tcg_gen_shift_imm = tcg_gen_shri_i64;
> +    }
> +
> +    tcg_gen_movi_i64(mask, 0xFFFFFFFF);
> +    tcg_gen_and_i64(a1, a, mask);
> +    tcg_gen_and_i64(b1, b, mask);
> +    tcg_gen_mul_i64(t, a1, b1);
> +    tcg_gen_shri_i64(k, t, 32);
> +
> +    tcg_gen_shift_imm(a1, a, 32);
> +    tcg_gen_mul_i64(t, a1, b1);
> +    tcg_gen_add_i64(t, t, k);
> +    tcg_gen_and_i64(k, t, mask);
> +    tcg_gen_shift_imm(w, t, 32);
> +
> +    tcg_gen_and_i64(a1, a, mask);
> +    tcg_gen_shift_imm(b1, b, 32);
> +    tcg_gen_mul_i64(t, a1, b1);
> +    tcg_gen_add_i64(t, t, k);
> +    tcg_gen_shift_imm(k, t, 32);
> +
> +    tcg_gen_shift_imm(a1, a, 32);
> +    tcg_gen_mul_i64(t, a1, b1);
> +    tcg_gen_add_i64(t, t, w);
> +    tcg_gen_add_i64(t, t, k);

You should be using tcg_gen_mul{s,u}2_i64 instead of open-coding the high-part 
multiplication.

r~