[Sbcl-help] Consing memory question with LET, FLOAT, SIN/COS

[Peter K. <ps...@cs...>]

Hello,

I'm writing some math codes, and in sbcl 1.3.15 on linux xubuntu 16.04LTS
x86_64 and I get some unexpected consing. Maybe you all can help explain what
I'm doing that is causing it. I have some test cases in the REPL:

;; defined at the repl

(defun test1 (arg1 arg2)
  (let ((a (float (cos arg1) 1.0))
        (b (float (sin arg2) 1.0)))
    (values a b)))

(defun test2 (arg1 arg2)
  (let ((a (cos arg1))
        (b (sin arg2)))
    (values a b)))

(defun test3 (arg1 arg2)
  (let ((a (float arg1 1.0))
        (b (float arg2 1.0)))
    (values a b)))

CL-USER> (time (loop repeat 1000000 do (test1 (/ pi 6) (/ pi 6))))
Evaluation took:
  0.095 seconds of real time
  0.093334 seconds of total run time (0.093334 user, 0.000000 system)
  [ Run times consist of 0.010 seconds GC time, and 0.084 seconds non-GC time. ]
  97.89% CPU
  285,006,444 processor cycles
  32,014,336 bytes consed

NIL
CL-USER> (time (loop repeat 1000000 do (test2 (/ pi 6) (/ pi 6))))
Evaluation took:
  0.080 seconds of real time
  0.080000 seconds of total run time (0.080000 user, 0.000000 system)
  100.00% CPU
  239,210,455 processor cycles
  31,981,568 bytes consed

NIL
CL-USER> (time (loop repeat 1000000 do (test3 (/ pi 6) (/ pi 6))))
Evaluation took:
  0.027 seconds of real time
  0.030000 seconds of total run time (0.030000 user, 0.000000 system)
  111.11% CPU
  82,407,547 processor cycles
  0 bytes consed

NIL


However, and curiously, this doesn't cons:


VAO> (time
 (loop repeat 1000000 do
   (funcall (lambda (arg1 arg2)
              (let ((a (float (sin arg1) 1.0))
                    (b (float (cos arg2) 1.0)))
                (values a b)))
	    (/ pi 6) (/ pi 6))))
Evaluation took:
  0.001 seconds of real time
  0.000000 seconds of total run time (0.000000 user, 0.000000 system)
  0.00% CPU
  3,093,048 processor cycles
  0 bytes consed

NIL



Any help on what I'm doing wrong and how I can remove that consing?

Thank you!

-pete