Compilation of 7 line function does not terminate

[Paul F. Dietz]

(compile nil '(lambda (a c x)
  (declare (type (integer -2845880 670871950) a))
  (declare (type (integer -8797424583931 -3696228396) c))
  (declare (type (integer 0 1) x))
  (flet ((%f16 (f16-1)
           (max f16-1 -982044058 a -1354524299132 f16-1 2
                5038700212014375 -4553 749369815788340702
                35184372088832 106498931517480 c
                4611686018427387903)
           ))
    (logior (%f16
             (expt
              (+ (- (deposit-field c (byte 26 19) -6987))
                 (%f16 x)
                 x)
              2))
            49))))

==> does not terminate before I ran out of patience

This is cut down from a larger function produced by the random tester. On that function, the lisp eventually (over the weekend when I was running the tester) ran out of heap and dropped into ldb.

I wonder if the compiler is producing very large type terms somewhere.

[Paul F. Dietz (paul-f-dietz)]

Simplified example:

(compile nil
 '(lambda (c x)
   (declare (type fixnum c))
   (declare (type (integer 0 1) x))
   (flet ((%f16 (y) (max y y c)))
     (-
      (%f16
       (expt
        (+ (- (deposit-field c (byte 26 19) -1))
           (%f16 x))
        2))
      ))))

[Paul F. Dietz (paul-f-dietz)]

Tracing SB-C::TWO-ARG-DERIVE-TYPE show some extremely large bignums are being computed. I suggest type propagation give up if the bignums get too big, and just widen to INTEGER.

[Paul F. Dietz (paul-f-dietz)]

Even simpler:

(compile nil
 '(lambda (c)
   (declare (type fixnum c))
   (flet ((%f16 (y) (max y y c)))
     (- (%f16
         (expt
          (1+ (%f16 0))
          2))))))