Accelerate SVE128 SBGEMM/BGEMM

This accelerates SBGEMM/BGEMM by extending the existing 8x4 kernel to 8x8 (unrolling N by 8)

Not sure if it's a good idea to delete the previous 8x4 kernel?

Here are the speedups on single core Neoverse-V2 (SVE128) compared to prev state:

Per-shape speedup
  M=N=K=64: SBGEMM 1.164x (16.42%), BGEMM 1.133x (13.30%)
  M=N=K=128: SBGEMM 1.220x (22.02%), BGEMM 1.186x (18.56%)
  M=N=K=256: SBGEMM 1.241x (24.08%), BGEMM 1.235x (23.54%)
  M=N=K=512: SBGEMM 1.240x (23.95%), BGEMM 1.227x (22.75%)
  M=N=K=1024: SBGEMM 1.251x (25.11%), BGEMM 1.232x (23.23%)
  M=N=K=2048: SBGEMM 1.235x (23.47%), BGEMM 1.246x (24.64%)

Signed-off-by: Fadi Arafeh <fadi.arafeh@arm.com>

Author: fadara01

CONTRIBUTORS.md

@@ -272,3 +272,6 @@ In chronological order:
 
 * Anna Mayne <anna.mayne@arm.com>
   * [2025-11-19] Update thread throttling profile for SGEMV on NEOVERSEV1 and NEOVERSEV2
+
+* Fadi Arafeh <fadi.arafeh@arm.com>
+  * [2026-03-05] Accelerate SVE128 SBGEMM/BGEMM

kernel/arm64/KERNEL.NEOVERSEN2

@@ -191,25 +191,29 @@ ZGEMMOTCOPYOBJ =  zgemm_otcopy$(TSUFFIX).$(SUFFIX)
 ifeq ($(BUILD_BFLOAT16), 1)
 BGEMM_BETA    =  bgemm_beta_neon.c
 BGEMMKERNEL    = sbgemm_kernel_$(BGEMM_UNROLL_M)x$(BGEMM_UNROLL_N)_neoversen2.c
+ifneq ($(BGEMM_UNROLL_M), $(BGEMM_UNROLL_N))
 BGEMMINCOPY    = sbgemm_ncopy_$(BGEMM_UNROLL_M)_neoversen2.c
 BGEMMITCOPY    = sbgemm_tcopy_$(BGEMM_UNROLL_M)_neoversen2.c
-BGEMMONCOPY    = sbgemm_ncopy_$(BGEMM_UNROLL_N)_neoversen2.c
-BGEMMOTCOPY    = sbgemm_tcopy_$(BGEMM_UNROLL_N)_neoversen2.c
 BGEMMINCOPYOBJ =  bgemm_incopy$(TSUFFIX).$(SUFFIX)
 BGEMMITCOPYOBJ =  bgemm_itcopy$(TSUFFIX).$(SUFFIX)
+endif
+BGEMMONCOPY    = sbgemm_ncopy_$(BGEMM_UNROLL_N)_neoversen2.c
+BGEMMOTCOPY    = sbgemm_tcopy_$(BGEMM_UNROLL_N)_neoversen2.c
 BGEMMONCOPYOBJ =  bgemm_oncopy$(TSUFFIX).$(SUFFIX)
 BGEMMOTCOPYOBJ =  bgemm_otcopy$(TSUFFIX).$(SUFFIX)
 BGEMVTKERNEL = sbgemv_t_bfdot.c
 BGEMVNKERNEL = bgemv_n_sve_v3x4.c
 
 SBGEMM_BETA    =  sbgemm_beta_neoversen2.c
 SBGEMMKERNEL    = sbgemm_kernel_$(SBGEMM_UNROLL_M)x$(SBGEMM_UNROLL_N)_neoversen2.c
+ifneq ($(SBGEMM_UNROLL_M), $(SBGEMM_UNROLL_N))
 SBGEMMINCOPY    = sbgemm_ncopy_$(SBGEMM_UNROLL_M)_neoversen2.c
 SBGEMMITCOPY    = sbgemm_tcopy_$(SBGEMM_UNROLL_M)_neoversen2.c
-SBGEMMONCOPY    = sbgemm_ncopy_$(SBGEMM_UNROLL_N)_neoversen2.c
-SBGEMMOTCOPY    = sbgemm_tcopy_$(SBGEMM_UNROLL_N)_neoversen2.c
 SBGEMMINCOPYOBJ =  sbgemm_incopy$(TSUFFIX).$(SUFFIX)
 SBGEMMITCOPYOBJ =  sbgemm_itcopy$(TSUFFIX).$(SUFFIX)
+endif
+SBGEMMONCOPY    = sbgemm_ncopy_$(SBGEMM_UNROLL_N)_neoversen2.c
+SBGEMMOTCOPY    = sbgemm_tcopy_$(SBGEMM_UNROLL_N)_neoversen2.c
 SBGEMMONCOPYOBJ =  sbgemm_oncopy$(TSUFFIX).$(SUFFIX)
 SBGEMMOTCOPYOBJ =  sbgemm_otcopy$(TSUFFIX).$(SUFFIX)
 SBGEMVTKERNEL = sbgemv_t_bfdot.c

kernel/arm64/sbgemm_kernel_8x8_neoversen2.c

@@ -0,0 +1,56 @@
+/***************************************************************************
+ * Copyright (c) 2026 The OpenBLAS Project
+ * All rights reserved.
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in
+ * the documentation and/or other materials provided with the
+ * distribution.
+ * 3. Neither the name of the OpenBLAS project nor the names of
+ * its contributors may be used to endorse or promote products
+ * derived from this software without specific prior written permission.
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE OPENBLAS PROJECT OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * *****************************************************************************/
+
+#include <arm_sve.h>
+#include <arm_neon.h>
+
+#include "common.h"
+
+#define ALPHA_ONE
+#include "sbgemm_kernel_8x8_neoversen2_impl.c"
+#undef ALPHA_ONE
+#undef UPDATE_C
+#include "sbgemm_kernel_8x8_neoversen2_impl.c"
+
+int CNAME(BLASLONG m, BLASLONG n, BLASLONG k, FLOAT alpha, IFLOAT *A, IFLOAT *B,
+          FLOAT *C, BLASLONG ldc) {
+#ifdef BGEMM
+  bfloat16_t alpha_bf16;
+  memcpy(&alpha_bf16, &alpha, sizeof(bfloat16_t));
+  float alpha_f32 = vcvtah_f32_bf16(alpha_bf16);
+#else
+  float alpha_f32 = alpha;
+#endif
+
+  if (alpha_f32 == 1.0f)
+    return gemm_kernel_neoversen2_alpha_one(m, n, k, alpha, A, B, C, ldc);
+  else
+    return gemm_kernel_neoversen2_alpha(m, n, k, alpha, A, B, C, ldc);
+
+  return 0;
+}