INT-SAP is NIL when using translate-into-foreign-memory on SBCL

[Steven Nunez]

Greetings all,
I first sent this message to SBCL-bugs, since the code works on CCL. where they 
suggested it's an issue in CFFI. I'm hoping that someone here has an idea of 
what the problem is.
I'm wrapping some of the complex math functions in openlibm, and encounter the 
following stack trace when calling them:
The value
  NIL
is not of type
  SB-SYS:SYSTEM-AREA-POINTER
when binding SB-ALIEN::VALUE
...

  0: (CFFI::LIBFFI/CALL #.(SB-SYS:INT-SAP #X027C0610) NIL #.(SB-SYS:INT-SAP 
#X0574FFE0) #.(SB-SYS:INT-SAP #X0574FFF0))
      Locals:
        AVALUES = #.(SB-SYS:INT-SAP #X0574FFF0)
        FFI-CIF = #.(SB-SYS:INT-SAP #X027C0610)
        FUNCTION = NIL
        RVALUE = #.(SB-SYS:INT-SAP #X0574FFE0)

The FUNCTION parameter, which SBCL expects to be a INT-SAP, is NIL. All the 
other (non complex number) functions work, but those going through the 
foreign-memory functions fail.

Openlibm is is available on any linux distribution via the package manager, and 
on MS Windows via MSYS2. This is with SBCL 2.0.10 on MS Windows 10.To reproduce 
the issue:

(ql:quickload '(:cffi :cffi-libffi))

(cffi:define-foreign-library libm
  ;; (:windows (:or "libopenlibm"
  ;;            #.(cl:merge-pathnames "libopenlibm.dll" 
cl:*compile-file-pathname*)))
  (t (:default "libopenlibm")))
(cffi:load-foreign-library 'libm)

#+unix
(cffi:define-foreign-library libm
  (t (:default "libopenlibm")))


(cffi:defcstruct (complex-double-c :class complex-double-type)
      (dat :double :count 2))

(cl:defmethod cffi:translate-into-foreign-memory ((value cl:complex) (type 
complex-double-type) p)
  (cffi:with-foreign-slots ((dat) p (:struct complex-double-c))
    (cl:setf (cffi:mem-aref dat :double 0) (cl:realpart value)
         (cffi:mem-aref dat :double 1) (cl:imagpart value))))

(cl:defmethod cffi:translate-from-foreign (p (type complex-double-type))
  (cffi:with-foreign-slots ((dat) p (:struct complex-double-c))
    (cl:complex (cffi:mem-aref dat :double 0)
        (cffi:mem-aref dat :double 1))))

(cffi:defcfun "cacos" (:struct complex-double-c) (c (:struct complex-double-c)))

;;; Try to call the function via CFFI
(cacos #C(0.16340015462715485d0 0.35359829928359165d0))

;;; Lower level version of the above
(cl:defun complex-acos (c)
  (cffi:foreign-funcall "casos"
            (:struct complex-double-c) c (:struct complex-double-c)))
(complex-acos #C(0.16340015462715485d0 0.35359829928359165d0))
Any ideas?