update comment

msccl/language/instruction_dag.py

@@ -55,7 +55,7 @@ def circular_dep_after_merge(op: Op, other_op: Op):
 
 """
 For case: op2.prev = [op1, op3]. op1.next = [op2]. op3.next = [op2]. And op1 and op2 are satisfied to merge.
-We only apply the merge if all previous ops of op2 are visited after the merge.
+We only apply the merge if all previous ops of op2 are visited. (op1 is the last previous op of op2).
 """
 def all_prevs_visited_after_merge(op: Op, other_op: Op):
     step = op.step