bug#26047: 26.0.50; emacs crash by cl-caff2

[Andreas Politz]

Here is a test case.

(ert-deftest byte-code-optimzier-1 ()
  (let* ((el-file (make-temp-file "test" nil ".el"))
         (elc-file (concat (file-name-sans-extension el-file) ".elc")))
    (unwind-protect
        (let ((byte-compile-warnings t))
          (with-temp-file el-file
            (dolist (form '((require 'cl-lib)
                            (put 's 'buf "abcd")
                            (cl-callf2 cl-concatenate 'string (get 's 'buf) 
"efg")
                            (provide 't)))
              (insert (prin1-to-string form))
              (insert "\n")))
          (byte-compile-file el-file)
          (should (progn (load-file elc-file) t)))
      (when (file-exists-p el-file)
        (delete-file el-file))
      (when (file-exists-p elc-file)
        (delete-file elc-file)))))

-ap