[Mesa-dev] [PATCH 2/4] i965: Provide sse2 version for rgba8 <-> bgra8 swizzle

[Matt Turner]

On Sun, Jan 17, 2016 at 1:49 PM,  <sroland at vmware.com> wrote:
> From: Roland Scheidegger <sroland at vmware.com>
>
> The existing code used ssse3, and because it isn't compiled in a separate
> file compiled with that, it is usually not used (that, of course, could
> be fixed...), whereas sse2 is always present at least with 64bit builds.
> It is actually trivial to do with sse2 without pshufb, on some cpus (I'm
> looking at you, atom!) it might not even be slower.
> This is compile-tested only, it doesn't actually do what I really want
> (which is glReadPixels without doing byte access from an uncached region,
> which is what you'll get on intel chips not having llc, if your cpu doesn't
> support sse41 (in which case the rb would be copied over with movntdqa instead
> of mapped, so mesa format_utils byte swapping conversion will then access
> the cached region instead of the uncached one) - really need sse2-optimized
> convert_ubyte functions for a proper fix, otherwise google maps in firefox is
> reduced to fps below 1 fps), but hey why not. I don't have a gpu which could
> possibly hit this, albeit I succesfully used the exact same code elsewhere.

Bah, wall of text!

I don't think we need all this. The commit title says everything I
think it needs to say.

> v2: fix andnot argument order, add comments
> ---
>  src/mesa/drivers/dri/i965/intel_mipmap_tree.c  | 18 +++++++
>  src/mesa/drivers/dri/i965/intel_tiled_memcpy.c | 73 +++++++++++++++++++++-----
>  2 files changed, 79 insertions(+), 12 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/intel_mipmap_tree.c b/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
> index 108dd87..5fc4212 100644
> --- a/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
> +++ b/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
> @@ -2773,6 +2773,24 @@ intel_miptree_map(struct brw_context *brw,
>     } else if (!(mode & GL_MAP_WRITE_BIT) &&
>                !mt->compressed && cpu_has_sse4_1 &&
>                (mt->pitch % 16 == 0)) {
> +      /*
> +       * XXX: without sse4_1, in some situations still really want to copy
> +       * regardless. Presumably this is not done for performance reasons -
> +       * with movntdqa thanks to the 64byte streaming load buffer the
> +       * uncached->cached copy followed by cached->cached later is always
> +       * faster than doing "ordinary" uncached->cached copy.
> +       * Without movntdqa, of course an additional copy doesn't help, albeit
> +       * it has to be said the uncached->cached one is an order of magnitude
> +       * slower than the later cached->cached one in any case.
> +       * But mesa may not do a simple memcpy on that memory later - some
> +       * glReadPixels paths for instance will well hit per-byte access which
> +       * is a complete performance killer on uncached memory. So in these
> +       * cases really want to copy regardless, unless the map below could
> +       * play some tricks making the memory cached.
> +       * (Or otherwise ensure mesa can't hit these paths often, for instance
> +       * glReadPixels requiring conversions could be handled by meta, so in
> +       * end it really would be just memcpy.)
> +       */

Walls of text are really hard to read...

I don't think adding this comment to the code is particularly
valuable, but it does make me wonder if we should just add a memcpy
fallback after this path? Maybe we don't care once we have this patch.

>        intel_miptree_map_movntdqa(brw, mt, map, level, slice);
>  #endif
>     } else {
> diff --git a/src/mesa/drivers/dri/i965/intel_tiled_memcpy.c b/src/mesa/drivers/dri/i965/intel_tiled_memcpy.c
> index 2383401..42fdde1 100644
> --- a/src/mesa/drivers/dri/i965/intel_tiled_memcpy.c
> +++ b/src/mesa/drivers/dri/i965/intel_tiled_memcpy.c
> @@ -36,10 +36,13 @@
>  #include "brw_context.h"
>  #include "intel_tiled_memcpy.h"
>
> -#ifdef __SSSE3__
> +#if defined(__SSSE3__)
>  #include <tmmintrin.h>
> +#elif defined(__SSE2__)
> +#include <emmintrin.h>
>  #endif
>
> +
>  #define FILE_DEBUG_FLAG DEBUG_TEXTURE
>
>  #define ALIGN_DOWN(a, b) ROUND_DOWN_TO(a, b)
> @@ -56,23 +59,69 @@ static const uint32_t ytile_width = 128;
>  static const uint32_t ytile_height = 32;
>  static const uint32_t ytile_span = 16;
>
> -#ifdef __SSSE3__
> +#if defined(__SSSE3__)
>  static const uint8_t rgba8_permutation[16] =
>     { 2,1,0,3, 6,5,4,7, 10,9,8,11, 14,13,12,15 };
>
>  /* NOTE: dst must be 16-byte aligned. src may be unaligned. */
> -#define rgba8_copy_16_aligned_dst(dst, src)                            \
> -   _mm_store_si128((__m128i *)(dst),                                   \
> -                   _mm_shuffle_epi8(_mm_loadu_si128((__m128i *)(src)), \
> -                                    *(__m128i *) rgba8_permutation))
> +static inline void
> +rgba8_copy_16_aligned_dst(void *dst, const void *src)
> +{
> +   __m128i reg;
> +   reg = _mm_loadu_si128((__m128i *)src);
> +   reg = _mm_shuffle_epi8(reg, *(__m128i *)rgba8_permutation);
> +   _mm_store_si128((__m128i *)dst, reg);

Here, and...

> +}
>
>  /* NOTE: src must be 16-byte aligned. dst may be unaligned. */
> -#define rgba8_copy_16_aligned_src(dst, src)                            \
> -   _mm_storeu_si128((__m128i *)(dst),                                  \
> -                    _mm_shuffle_epi8(_mm_load_si128((__m128i *)(src)), \
> -                                     *(__m128i *) rgba8_permutation))
> +static inline void
> +rgba8_copy_16_aligned_src(void *dst, const void *src)
> +{
> +   __m128i reg;
> +   reg = _mm_load_si128((__m128i *)src);
> +   reg = _mm_shuffle_epi8(reg, *(__m128i *)rgba8_permutation);
> +   _mm_storeu_si128((__m128i *)dst, reg);

... here, I'd just make these single statements like they were before.
They fit easily within 80 columns.

> +}
> +
> +#elif defined(__SSE2__)
> +static inline void
> +rgba8_copy_16_aligned_dst(void *dst, const void *src)
> +{
> +   __m128i srcreg, dstreg, agmask, ag, rb, r, b;
> +
> +   agmask = _mm_set1_epi32(0xFF00FF00);
> +   srcreg = _mm_loadu_si128((__m128i *)src);

Okay, so we're starting with 0xAABBGGRR.

> +
> +   rb = _mm_andnot_si128(agmask, srcreg);

Produces 0x00BB00GG. Looks good.

> +   ag = _mm_and_si128(agmask, srcreg);

Produces 0xAA00GG00. Looks good.

> +   r = _mm_srli_epi32(rb, 16);

Produces 0x000000BB. Looks wrong -- should be b, not r.

> +   b = _mm_slli_epi32(rb, 16);

Produces 0x00RR0000. Looks wrong -- should be r, not b.

> +   dstreg = _mm_or_si128(ag, r);
> +   dstreg = _mm_or_si128(dstreg, b);

I think we can do this better. Instead of two shifts and two ORs,
recognizing that the R and B values in rb have 8-bits of zero padding,
we can use _mm_shufflehi_epi16/_mm_shufflelo_epi16 and then a single
OR:

br = _mm_shufflehi_epi16(_mm_shufflelo_epi16(rb, _MM_SHUFFLE(2, 3, 0,
1)), _MM_SHUFFLE(2, 3, 0, 1));
dstreg = _mm_or_si128(ag, br);

(appropriately line wrapped)

> +
> +   _mm_store_si128((__m128i *)dst, dstreg);
> +}
> +
> +static inline void
> +rgba8_copy_16_aligned_src(void *dst, const void *src)
> +{
> +   __m128i srcreg, dstreg, agmask, ag, rb, r, b;
> +
> +   agmask = _mm_set1_epi32(0xFF00FF00);
> +   srcreg = _mm_load_si128((__m128i *)src);
> +
> +   rb = _mm_andnot_si128(agmask, srcreg);
> +   ag = _mm_and_si128(agmask, srcreg);
> +   r = _mm_srli_epi32(rb, 16);
> +   b = _mm_slli_epi32(rb, 16);
> +   dstreg = _mm_or_si128(ag, r);
> +   dstreg = _mm_or_si128(dstreg, b);

Same comments here.

With the walls of text removed, and the other couple of things
addressed, this patch would be

Reviewed-by: Matt Turner <mattst88 at gmail.com>