digraph Memory {
  rankdir=BT;
  node [shape=box];
  M [label="Initial memory"];
  X [label="Store x = 42"];
  Y [label="Loop: Store y"];
  L [label="Load x (42)"];
  L -> X -> M [color=blue]; Y -> M [color=green];
  MemMerge -> X [color=blue]; MemMerge -> Y [color=green];
  Return -> MemMerge; Return -> L;
  { rank=same; MemMerge -> L [style=invis]; }
  Y -> X [style=invis]; // Layout only: keep the stores in code order.
}