Open coding coercion to (complex double-float) not implemented.

[Mark Cox]

The compiler complains that it is unable to open code the coercion from a double-float to a complex double-float in the following

  (defun copy-to/slow (output input)
    (declare (type (simple-array (complex double-float) (*)) output)
             (type (simple-array double-float (*)) input)
             (optimize (speed 3) (safety 1) (debug 1)))
    (dotimes (i (length output))
      (setf (aref output i) (coerce (aref input i)
                                    '(complex double-float))))
    output)

As a result, the function COPY-TO/SLOW conses substantially.

If the coercion is replaced with (COMPLEX (AREF INPUT I)), it does not complain

  (defun copy-to/fast (output input)
    (declare (type (simple-array (complex double-float) (*)) output)
             (type (simple-array double-float (*)) input)
             (optimize (speed 3) (safety 1) (debug 1)))
    (dotimes (i (length output))
      (setf (aref output i) (complex (aref input i))))
    output)

This function performs no consing as expected.

[Stas Boukarev (stassats)]

In aab5bd0d43016a52b5cf0df34885f0d97b03a804, both produce the same code.