Exception for Commute and associate

Math

\[\left(\left(x + y\right) + z\right) - \left(x + \left(y + z\right)\right)\]

C

double f(double x, double y, double z) {
        double r7972 = x;
        double r7973 = y;
        double r7974 = r7972 + r7973;
        double r7975 = z;
        double r7976 = r7974 + r7975;
        double r7977 = r7973 + r7975;
        double r7978 = r7972 + r7977;
        double r7979 = r7976 - r7978;
        return r7979;
}

Reproduce

Please include this information when filing a bug report:

herbie shell --seed 2019191 
(FPCore (x y z)
  :name "Commute and associate"
  (- (+ (+ x y) z) (+ x (+ y z))))

Backtrace

get-representation: Unknown representation #f		L	C
loop	/data/pavpan/nightlies/herbie/interface2/src/points.rkt	122	4
prepare-points	/data/pavpan/nightlies/herbie/interface2/src/points.rkt	146	0
setup-prog!34	/data/pavpan/nightlies/herbie/interface2/src/mainloop.rkt	67	0
run-improve43	/data/pavpan/nightlies/herbie/interface2/src/mainloop.rkt	339	0
(unnamed)	/opt/racket-7.0/collects/racket/private/more-scheme.rkt	261	28
run	/opt/racket-7.0/share/pkgs/profile-lib/main.rkt	39	2
profile-thunk16	/opt/racket-7.0/share/pkgs/profile-lib/main.rkt	9	0
(unnamed)	/opt/racket-7.0/collects/racket/private/more-scheme.rkt	261	28