Function: byte-compile-push-bytecodes

byte-compile-push-bytecodes is a macro defined in bytecomp.el.gz.

Signature

(byte-compile-push-bytecodes BYTE1 BYTE2 ... BYTEn BVAR CVAR)

Documentation

Push bytes onto BVAR, and increment CVAR by the number of bytes pushed.

BVAR and CVAR are variables which are updated after evaluating all the arguments.

Source Code

;; Defined in /usr/src/emacs/lisp/emacs-lisp/bytecomp.el.gz
;;; lapcode generator
;;
;; the byte-compiler now does source -> lapcode -> bytecode instead of
;; source -> bytecode, because it's a lot easier to make optimizations
;; on lapcode than on bytecode.
;;
;; Elements of the lapcode list are of the form (<instruction> . <parameter>)
;; where instruction is a symbol naming a byte-code instruction,
;; and parameter is an argument to that instruction, if any.
;;
;; The instruction can be the pseudo-op TAG, which means that this position
;; in the instruction stream is a target of a goto.  (car PARAMETER) will be
;; the PC for this location, and the whole instruction "(TAG pc)" will be the
;; parameter for some goto op.
;;
;; If the operation is varbind, varref, varset or push-constant, then the
;; parameter is (variable/constant . index_in_constant_vector).
;;
;; First, the source code is macroexpanded and optimized in various ways.
;; Then the resultant code is compiled into lapcode.  Another set of
;; optimizations are then run over the lapcode.  Then the variables and
;; constants referenced by the lapcode are collected and placed in the
;; constants-vector.  (This happens now so that variables referenced by dead
;; code don't consume space.)  And finally, the lapcode is transformed into
;; compacted byte-code.
;;
;; A distinction is made between variables and constants because the variable-
;; referencing instructions are more sensitive to the variables being near the
;; front of the constants-vector than the constant-referencing instructions.
;; Also, this lets us notice references to free variables.

(defmacro byte-compile-push-bytecodes (&rest args)
  "Push bytes onto BVAR, and increment CVAR by the number of bytes pushed.
BVAR and CVAR are variables which are updated after evaluating
all the arguments.

\(fn BYTE1 BYTE2 ... BYTEn BVAR CVAR)"
  (let ((byte-exprs (butlast args 2))
	(bytes-var (car (last args 2)))
	(pc-var (car (last args))))
    `(setq ,bytes-var ,(if (null (cdr byte-exprs))
                           `(progn (cl-assert (<= 0 ,(car byte-exprs)))
                                   (cons ,@byte-exprs ,bytes-var))
                         `(nconc (list ,@(reverse byte-exprs)) ,bytes-var))
           ,pc-var (+ ,(length byte-exprs) ,pc-var))))