Try to make sum_state_features faster

spacy/syntax/nn_parser.pyx

@@ -165,16 +165,17 @@ cdef void sum_state_features(float* output,
     cdef const float* feature
     padding = cached
     cached += F * O
+    cdef int id_stride = F*O
+    cdef float one = 1.
     for b in range(B):
         for f in range(F):
             if token_ids[f] < 0:
                 feature = &padding[f*O]
             else:
-                idx = token_ids[f] * F * O + f*O
+                idx = token_ids[f] * id_stride + f*O
                 feature = &cached[idx]
-            VecVec.add_i(output,
-                feature, 1., O)
-        output += O
+            openblas.simple_axpy(&output[b*O], O,
+                feature, one)
         token_ids += F