Re: [Qemu-devel] [PATCH v6 1/3] target/ppc: Optimize emulation of vpkpx instruction

[Richard Henderson]

On 8/27/19 2:37 AM, Stefan Brankovic wrote:
> +    for (i = 0; i < 4; i++) {
> +        switch (i) {
> +        case 0:
> +            /*
> +             * Get high doubleword of vA to perfrom 6-5-5 pack of pixels
> +             * 1 and 2.
> +             */
> +            get_avr64(avr, VA, true);
> +            tcg_gen_movi_i64(result, 0x0ULL);
> +            break;
> +        case 1:
> +            /*
> +             * Get low doubleword of vA to perfrom 6-5-5 pack of pixels
> +             * 3 and 4.
> +             */
> +            get_avr64(avr, VA, false);
> +            break;
> +        case 2:
> +            /*
> +             * Get high doubleword of vB to perfrom 6-5-5 pack of pixels
> +             * 5 and 6.
> +             */
> +            get_avr64(avr, VB, true);
> +            tcg_gen_movi_i64(result, 0x0ULL);
> +            break;
> +        case 3:
> +            /*
> +             * Get low doubleword of vB to perfrom 6-5-5 pack of pixels
> +             * 7 and 8.
> +             */
> +            get_avr64(avr, VB, false);
> +            break;
> +        }
> +        /* Perform the packing for 2 pixels(each iteration for 1). */
> +        tcg_gen_movi_i64(tmp, 0x0ULL);
> +        for (j = 0; j < 2; j++) {
> +            tcg_gen_shri_i64(shifted, avr, (j * 16 + 3));
> +            tcg_gen_andi_i64(shifted, shifted, mask1 << (j * 16));
> +            tcg_gen_or_i64(tmp, tmp, shifted);
> +
> +            tcg_gen_shri_i64(shifted, avr, (j * 16 + 6));
> +            tcg_gen_andi_i64(shifted, shifted, mask2 << (j * 16));
> +            tcg_gen_or_i64(tmp, tmp, shifted);
> +
> +            tcg_gen_shri_i64(shifted, avr, (j * 16 + 9));
> +            tcg_gen_andi_i64(shifted, shifted, mask3 << (j * 16));
> +            tcg_gen_or_i64(tmp, tmp, shifted);
> +        }
> +        if ((i == 0) || (i == 2)) {
> +            tcg_gen_shli_i64(tmp, tmp, 32);
> +        }
> +        tcg_gen_or_i64(result, result, tmp);
> +        if (i == 1) {
> +            /* Place packed pixels 1:4 to high doubleword of vD. */
> +            tcg_gen_mov_i64(result1, result);
> +        }
> +        if (i == 3) {
> +            /* Place packed pixels 5:8 to low doubleword of vD. */
> +            tcg_gen_mov_i64(result2, result);
> +        }
> +    }
> +    set_avr64(VT, result1, true);
> +    set_avr64(VT, result2, false);

I really have a hard time believing that it is worthwhile to inline all of this
code.  By my count this is 82 non-move opcodes.  That is a *lot* of inline
expansion.

However, I can well imagine that the existing out-of-line helper is less than
optimal.

> -void helper_vpkpx(ppc_avr_t *r, ppc_avr_t *a, ppc_avr_t *b)
> -{
> -    int i, j;
> -    ppc_avr_t result;
> -#if defined(HOST_WORDS_BIGENDIAN)
> -    const ppc_avr_t *x[2] = { a, b };
> -#else
> -    const ppc_avr_t *x[2] = { b, a };
> -#endif
> -
> -    VECTOR_FOR_INORDER_I(i, u64) {
> -        VECTOR_FOR_INORDER_I(j, u32) {
> -            uint32_t e = x[i]->u32[j];

Double indirect loads?

> -
> -            result.u16[4 * i + j] = (((e >> 9) & 0xfc00) |
> -                                     ((e >> 6) & 0x3e0) |
> -                                     ((e >> 3) & 0x1f));

Store to temporary ...

> -        }
> -    }
> -    *r = result;

... and then copy?

Try replacing the existing helper with something like the following.


r~



static inline uint64_t pkpx_1(uint64_t a, int shr, int shl)
{
    uint64_t r;

    r  = ((a >> (shr + 9)) & 0x3f) << shl;
    r |= ((a >> (shr + 6)) & 0x1f) << shl;
    r |= ((a >> (shr + 3)) & 0x1f) << shl;

    return r;
}

static inline uint64_t pkpx_2(uint64_t ah, uint64_t al)
{
    return pkpx_1(ah, 32, 48)
         | pkpx_1(ah,  0, 32)
         | pkpx_1(al, 32, 16)
         | pkpx_1(al,  0,  0);
}

void helper_vpkpx(uint64_t *r, uint64_t *a, uint64_t *b)
{
    uint64_t rh = pkpx_2(a->VsrD(0), a->VsrD(1));
    uint64_t rl = pkpx_2(b->VsrD(0), b->VsrD(1));
    r->VsrD(0) = rh;
    r->VsrD(1) = rl;
}