[CLJ-1111] Loops returning primtives are boxed even in return position

Sat, 22 Dec 2012 09:53:50 -0600

Reported here: https://groups.google.com/d/topic/clojure/atoFzbyuyos/discussion

(defn first-bit?
  {:inline (fn [n] `(== 1 (clojure.lang.Numbers/and ~n, 1)) )}
  [^long n]
  (== 1 (clojure.lang.Numbers/and n, 1)))

(defn exp-int
  ^double [^double x, ^long c]
  (loop [result 1.0, factor x, c c]
    (if (> c 0)
        (recur
         (if (first-bit? c)
           (* result factor)
           result),
         (* factor factor),
         (bit-shift-right c 1))
      result)))

Last lines of the Java bytecode of `exp-int`:

59 dload 5;               /* result */
61 invokestatic 40;       /* java.lang.Double java.lang.Double.valueOf(double c) */
64 checkcast 85;          /* java.lang.Number */
67 invokevirtual 89;      /* double doubleValue() */
70 dreturn;

The compiler doesn't currently infer the primitive type as soon as there is a recur:

(use '[clojure.contrib.repl-utils :only [expression-info]])
(expression-info '(loop [a 1] a))
;=> {:class long, :primitive? true}
(expression-info '(loop [a 1] (if true a (recur a)))
;=> nil

Patch attached.

Clojure JIRA

[CLJ-1111] Loops returning primtives are boxed even in return position