[Armedbear-devel] Incorrect (un)dead-code-elimination

Douglas Katzman dougk at google.com
Mon Apr 21 16:22:28 UTC 2014

;; In the test below, COMPUTE-INSIDES should be called by EXAMP-FAIL

java -jar abcl-bin-1.3.0/abcl.jar
CL-USER(1): (defmacro ultra-fancy-macro (&optional (x 'compute-insides))
                     (list 'cons ''loop (list x)))

CL-USER(2): (defun examp-fail (directives)
                    (labels ((compute-insides () '((here-are-the-guts)))
                                (compute-loop () (ultra-fancy-macro)))
; Note: deleting unused local function LABELS COMPUTE-INSIDES

CL-USER(3): (examp-fail nil) ; just checking.. maybe the Note was wrong?
(examp-fail nil)
#<THREAD "interpreter" {652D03DC}>: 
Debugger invoked on condition of type UNDEFINED-FUNCTION
  The function COMPUTE-INSIDES is undefined.
 3: TOP-LEVEL    Return to top level.
[1] CL-USER(4): 3

CL-USER(5): (defun examp-works (directives)
                     (labels ((compute-insides () '((here-are-the-guts)))
                                 (compute-loop () (ultra-fancy-macro)))
                      #'compute-insides ; spuriously reference it

CL-USER(6): (examp-works nil)

Without a statically observable use of compute-insides it is considered unused.
Macros have expanded *before* deciding that.
It is clear that the macro expands correctly based on 'examp-works'

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