Better hmin/hmax algorithms for SSE/AVX2 (#510)

Use a formulation that automatically produces the same result in all lanes, avoiding a separate broadcast step. The same approach would work with floats in principle, but it's not guaranteed to give the same result in all lanes when NaNs are involved (due to the way MINPS/MAXPS are defined), so leave the float versions alone for now. About 1% encode time reduction encoding a 8192x8192 test texture at 6x6 -thorough on a Ryzen 7950X3D. Co-authored-by: Fabian Giesen <[email protected]> Co-authored-by: Pete Harris <[email protected]>
ARM-software · Nov 4, 2024 · 521179c · 521179c
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commit 521179c
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Showing 2 changed files with 16 additions and 18 deletions.
diff --git a/Source/astcenc_vecmathlib_avx2_8.h b/Source/astcenc_vecmathlib_avx2_8.h
@@ -458,13 +458,12 @@ ASTCENC_SIMD_INLINE vint8 max(vint8 a, vint8 b)
  */
 ASTCENC_SIMD_INLINE vint8 hmin(vint8 a)
 {
-	__m128i m = _mm_min_epi32(_mm256_extracti128_si256(a.m, 0), _mm256_extracti128_si256(a.m, 1));
-	m = _mm_min_epi32(m, _mm_shuffle_epi32(m, _MM_SHUFFLE(0,0,3,2)));
-	m = _mm_min_epi32(m, _mm_shuffle_epi32(m, _MM_SHUFFLE(0,0,0,1)));
-	m = _mm_shuffle_epi32(m, _MM_SHUFFLE(0,0,0,0));
+	// Build min within groups of 2, then 4, then 8
+	__m256i m = _mm256_min_epi32(a.m, _mm256_shuffle_epi32(a.m, _MM_SHUFFLE(2, 3, 0, 1)));
+	m = _mm256_min_epi32(m, _mm256_shuffle_epi32(m, _MM_SHUFFLE(1, 0, 3, 2)));
+	m = _mm256_min_epi32(m, _mm256_permute2x128_si256(m, m, 0x01));
 
-	__m256i r = astcenc_mm256_set_m128i(m, m);
-	vint8 vmin(r);
+	vint8 vmin(m);
 	return vmin;
 }
 
@@ -481,13 +480,12 @@ ASTCENC_SIMD_INLINE int hmin_s(vint8 a)
  */
 ASTCENC_SIMD_INLINE vint8 hmax(vint8 a)
 {
-	__m128i m = _mm_max_epi32(_mm256_extracti128_si256(a.m, 0), _mm256_extracti128_si256(a.m, 1));
-	m = _mm_max_epi32(m, _mm_shuffle_epi32(m, _MM_SHUFFLE(0,0,3,2)));
-	m = _mm_max_epi32(m, _mm_shuffle_epi32(m, _MM_SHUFFLE(0,0,0,1)));
-	m = _mm_shuffle_epi32(m, _MM_SHUFFLE(0,0,0,0));
+	// Build max within groups of 2, then 4, then 8
+	__m256i m = _mm256_max_epi32(a.m, _mm256_shuffle_epi32(a.m, _MM_SHUFFLE(2, 3, 0, 1)));
+	m = _mm256_max_epi32(m, _mm256_shuffle_epi32(m, _MM_SHUFFLE(1, 0, 3, 2)));
+	m = _mm256_max_epi32(m, _mm256_permute2x128_si256(m, m, 0x01));
 
-	__m256i r = astcenc_mm256_set_m128i(m, m);
-	vint8 vmax(r);
+	vint8 vmax(m);
 	return vmax;
 }
 

diff --git a/Source/astcenc_vecmathlib_sse_4.h b/Source/astcenc_vecmathlib_sse_4.h
@@ -606,19 +606,19 @@ ASTCENC_SIMD_INLINE vint4 max(vint4 a, vint4 b)
  */
 ASTCENC_SIMD_INLINE vint4 hmin(vint4 a)
 {
-	a = min(a, vint4(_mm_shuffle_epi32(a.m, _MM_SHUFFLE(0, 0, 3, 2))));
-	a = min(a, vint4(_mm_shuffle_epi32(a.m, _MM_SHUFFLE(0, 0, 0, 1))));
-	return vint4(_mm_shuffle_epi32(a.m, _MM_SHUFFLE(0, 0, 0, 0)));
+	a = min(a, vint4(_mm_shuffle_epi32(a.m, _MM_SHUFFLE(2, 3, 0, 1))));
+	a = min(a, vint4(_mm_shuffle_epi32(a.m, _MM_SHUFFLE(1, 0, 3, 2))));
+	return a;
 }
 
 /*
  * @brief Return the horizontal maximum of a vector.
  */
 ASTCENC_SIMD_INLINE vint4 hmax(vint4 a)
 {
-	a = max(a, vint4(_mm_shuffle_epi32(a.m, _MM_SHUFFLE(0, 0, 3, 2))));
-	a = max(a, vint4(_mm_shuffle_epi32(a.m, _MM_SHUFFLE(0, 0, 0, 1))));
-	return vint4(_mm_shuffle_epi32(a.m, _MM_SHUFFLE(0, 0, 0, 0)));
+	a = max(a, vint4(_mm_shuffle_epi32(a.m, _MM_SHUFFLE(2, 3, 0, 1))));
+	a = max(a, vint4(_mm_shuffle_epi32(a.m, _MM_SHUFFLE(1, 0, 3, 2))));
+	return a;
 }
 
 /**