Comment 2 for bug 308945

I forgot to illustrate the behavior with the patch. So, here it is:

* (loop with stack = (make-array 2 :fill-pointer 2 :initial-element t)
          for length = (length stack)
          while (plusp length)
          for element = (vector-pop stack)
          collect element)

debugger invoked on a SB-INT:SIMPLE-PROGRAM-ERROR in thread #<THREAD
                                                              "initial thread" RUNNING
                                                              {A9DF7F1}>:
  iteration in LOOP follows body code
current LOOP context: FOR ELEMENT = (VECTOR-POP STACK) COLLECT.

Type HELP for debugger help, or (SB-EXT:QUIT) to exit from SBCL.

restarts (invokable by number or by possibly-abbreviated name):
  0: [ABORT] Exit debugger, returning to top level.

(SB-LOOP::LOOP-ERROR "iteration in LOOP follows body code")[:EXTERNAL]
0]