[fixup] Add a comment about memory ops

Author: momchil-velikov

mlir/test/Integration/Dialect/Vector/CPU/ArmNeon/vector-contract-bfmmla.mlir

@@ -110,6 +110,10 @@ func.func @matrix_by_matrix_mul_and_acc() {
 //   * ACC, OUT: vector<Nxf32>
 // N is even and K is divisible by 4.
 // In this specific test we use N == 4, and K == 4.
+// Note: the seemingly unnecessary writes of test vectors to memory are done
+// in order to introduce memory load operations on the path leading up to
+// `vector.contract` since that's more representation of the typical usage
+// when multiplying big, non-constant tensors.
 
 // CHECK-IR-LABEL: llvm.func @vector_by_matrix_mul_and_acc
 // CHECK-IR-COUNT-2: arm_neon.intr.bfmmla