Section 2.3.2.4 describes it for Sandy Bridge (and the rules don't seem to have changed in later generations):

  The loops with the following attributes qualify for 
  LSD/micro-op queue replay:
  • Up to eight chunk fetches of 32-instruction-bytes.
  • Up to 28 micro-ops (~28 instructions).
  • All micro-ops are also resident in the Decoded ICache.
  • Can contain no more than eight taken branches and 
    none of them can be a CALL or RET.
  • Cannot have mismatched stack operations. For example,
    more PUSH than POP instructions.