cl-defsubst

cl-defsubst is an autoloaded Lisp macro in `cl-macs.el'.

(cl-defsubst NAME ARGLIST [DOCSTRING] BODY...)

Define NAME as a function.
Like `defun', except the function is automatically declared `inline' and
the arguments are immutable.
ARGLIST allows full Common Lisp conventions, and BODY is implicitly
surrounded by (cl-block NAME ...).
The function's arguments should be treated as immutable.