src: cpu: x64: matmul: add wei transposition workaround for input dim…

… size = 1

src/cpu/x64/matmul/brgemm_matmul_utils.cpp

@@ -175,6 +175,21 @@ status_t brgemm_matmul_conf_utils_t::set_or_check_B_tag(
                         blocked_16n_B_layout_tag)
                 : memory_desc_matches_one_of_tag(B_md, plain_tensor_layout_tag,
                         transposed_tensor_layout_tag, acbd, adbc);
+
+        // For cases when the weights tensor is transposed but has
+        // 'dim_size == 1', we can ignore transposition and compute as a plain
+        // format tensor. This removes the need of allocating a scratchpad for
+        // copy_B.
+        if (transposed_tensor_layout_tag == bgmmc.wei_tag) {
+            memory_desc_t B_md_plain;
+            const status_t status
+                    = dnnl_memory_desc_init_by_tag(&B_md_plain, B_md.ndims,
+                            B_md.dims, B_md.data_type, plain_tensor_layout_tag);
+            if (status != status::success) return status;
+            if (status == status::success && B_md_plain == B_md)
+                bgmmc.wei_tag = plain_tensor_layout_tag;
+        }
+
         if (format_tag::undef == bgmmc.wei_tag) return status::unimplemented;
     }