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Speed DispatchAlpha_SSE2 up

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On some dataset, this was taking 2.5%. 2% when switching to
_mm_maskmoveu_si128. 1.7% when using _mm_loadu_si128

Confirmed by IACA: going from throughput of 4.26 to 3.5 and then
to 6.26 for twice the input.

Change-Id: I409f901aaad9d39bf55a1aac28cc25f126876b01
This commit is contained in:
Vincent Rabaud 2025-04-10 11:52:42 +02:00
parent ee8e8c620f
commit 44f91b0ddd
1 changed files with 33 additions and 24 deletions
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57
src/dsp/alpha_processing_sse2.c
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@ -16,6 +16,8 @@
#if defined(WEBP_USE_SSE2)
#include <emmintrin.h>
#include "src/dsp/cpu.h"
//------------------------------------------------------------------------------
static int DispatchAlpha_SSE2(const uint8_t* WEBP_RESTRICT alpha,
@ -26,38 +28,44 @@ static int DispatchAlpha_SSE2(const uint8_t* WEBP_RESTRICT alpha,
uint32_t alpha_and = 0xff;
int i, j;
const __m128i zero = _mm_setzero_si128();
const __m128i rgb_mask = _mm_set1_epi32((int)0xffffff00); // to preserve RGB
const __m128i all_0xff = _mm_set_epi32(0, 0, ~0, ~0);
__m128i all_alphas = all_0xff;
const __m128i alpha_mask = _mm_set1_epi32((int)0xff); // to preserve A
const __m128i all_0xff = _mm_set1_epi8(0xff);
__m128i all_alphas16 = all_0xff;
__m128i all_alphas8 = all_0xff;
// We must be able to access 3 extra bytes after the last written byte
// 'dst[4 * width - 4]', because we don't know if alpha is the first or the
// last byte of the quadruplet.
const int limit = (width - 1) & ~7;
for (j = 0; j < height; ++j) {
__m128i* out = (__m128i*)dst;
for (i = 0; i < limit; i += 8) {
char* ptr = (char*)dst;
for (i = 0; i + 16 <= width - 1; i += 16) {
// load 16 alpha bytes
const __m128i a0 = _mm_loadu_si128((const __m128i*)&alpha[i]);
const __m128i a1_lo = _mm_unpacklo_epi8(a0, zero);
const __m128i a1_hi = _mm_unpackhi_epi8(a0, zero);
const __m128i a2_lo_lo = _mm_unpacklo_epi16(a1_lo, zero);
const __m128i a2_lo_hi = _mm_unpackhi_epi16(a1_lo, zero);
const __m128i a2_hi_lo = _mm_unpacklo_epi16(a1_hi, zero);
const __m128i a2_hi_hi = _mm_unpackhi_epi16(a1_hi, zero);
_mm_maskmoveu_si128(a2_lo_lo, alpha_mask, ptr + 0);
_mm_maskmoveu_si128(a2_lo_hi, alpha_mask, ptr + 16);
_mm_maskmoveu_si128(a2_hi_lo, alpha_mask, ptr + 32);
_mm_maskmoveu_si128(a2_hi_hi, alpha_mask, ptr + 48);
// accumulate 16 alpha 'and' in parallel
all_alphas16 = _mm_and_si128(all_alphas16, a0);
ptr += 64;
}
if (i + 8 <= width - 1) {
// load 8 alpha bytes
const __m128i a0 = _mm_loadl_epi64((const __m128i*)&alpha[i]);
const __m128i a1 = _mm_unpacklo_epi8(a0, zero);
const __m128i a2_lo = _mm_unpacklo_epi16(a1, zero);
const __m128i a2_hi = _mm_unpackhi_epi16(a1, zero);
// load 8 dst pixels (32 bytes)
const __m128i b0_lo = _mm_loadu_si128(out + 0);
const __m128i b0_hi = _mm_loadu_si128(out + 1);
// mask dst alpha values
const __m128i b1_lo = _mm_and_si128(b0_lo, rgb_mask);
const __m128i b1_hi = _mm_and_si128(b0_hi, rgb_mask);
// combine
const __m128i b2_lo = _mm_or_si128(b1_lo, a2_lo);
const __m128i b2_hi = _mm_or_si128(b1_hi, a2_hi);
// store
_mm_storeu_si128(out + 0, b2_lo);
_mm_storeu_si128(out + 1, b2_hi);
// accumulate eight alpha 'and' in parallel
all_alphas = _mm_and_si128(all_alphas, a0);
out += 2;
_mm_maskmoveu_si128(a2_lo, alpha_mask, ptr);
_mm_maskmoveu_si128(a2_hi, alpha_mask, ptr + 16);
// accumulate 8 alpha 'and' in parallel
all_alphas8 = _mm_and_si128(all_alphas8, a0);
i += 8;
}
for (; i < width; ++i) {
const uint32_t alpha_value = alpha[i];
@ -68,8 +76,9 @@ static int DispatchAlpha_SSE2(const uint8_t* WEBP_RESTRICT alpha,
dst += dst_stride;
}
// Combine the eight alpha 'and' into a 8-bit mask.
alpha_and &= _mm_movemask_epi8(_mm_cmpeq_epi8(all_alphas, all_0xff));
return (alpha_and != 0xff);
alpha_and &= _mm_movemask_epi8(_mm_cmpeq_epi8(all_alphas8, all_0xff)) & 0xff;
return (alpha_and != 0xff ||
_mm_movemask_epi8(_mm_cmpeq_epi8(all_alphas16, all_0xff)) != 0xffff);
}
static void DispatchAlphaToGreen_SSE2(const uint8_t* WEBP_RESTRICT alpha,