;;; comp.el --- compilation of Lisp code into native code -*- lexical-binding: t -*-

;; Copyright (C) 2019 Free Software Foundation, Inc.

;; Keywords: lisp
;; Package: emacs

;; This file is part of GNU Emacs.

;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.

;;; Code:

(require 'bytecomp)
(require 'cl-lib)
(require 'cl-extra)
(require 'subr-x)

(defgroup comp nil
  "Emacs Lisp native compiler."
  :group 'lisp)

(defconst comp-debug t)

(defconst comp-passes '(comp-recuparate-lap
                        comp-limplify)
  "Passes to be executed in order.")

(defconst comp-known-ret-types '((Fcons . cons)))

(defconst comp-mostly-pure-funcs
  '(% * + - / /= 1+ 1- < <= = > >= cons list % concat logand logcount logior
      lognot logxor regexp-opt regexp-quote string-to-char string-to-syntax
      symbol-name)
  "Functions on witch we do constant propagation."
  ;;  Is it acceptable to move into the compile time functions that are
  ;; allocating memory? (these are technically not side effect free)
)

(cl-defstruct comp-args
  (min nil :type number
       :documentation "Minimum number of arguments allowed")
  (max nil
       :documentation "Maximum number of arguments allowed
To be used when ncall-conv is nil.")
  (ncall-conv nil :type boolean
              :documentation "If t the signature is:
(ptrdiff_t nargs, Lisp_Object *args)"))

(cl-defstruct (comp-func (:copier nil))
  "Internal rapresentation for a function."
  (symbol-name nil
               :documentation "Function symbol's name")
  (c-func-name nil :type 'string
               :documentation "The function name in the native world")
  (func nil
        :documentation "Original form")
  (byte-func nil
             :documentation "Byte compiled version")
  (ir nil
      :documentation "Current intermediate rappresentation")
  (args nil :type 'comp-args)
  (frame-size nil :type 'number)
  (blocks () :type list
          :documentation "List of basic block")
  (limple-cnt -1 :type 'number
              :documentation "Counter to create ssa limple vars"))

(cl-defstruct (comp-mvar (:copier nil) (:constructor make--comp-mvar))
  "A meta-variable being a slot in the meta-stack."
  (id nil :type number
     :documentation "SSA number")
  (slot nil :type fixnum
        :documentation "Slot position")
  (const-vld nil
             :documentation "Valid signal for the following slot")
  (constant nil
            :documentation "When const-vld non nil this is used for constant
 propagation")
  (type nil
        :documentation "When non nil is used for type propagation"))

(cl-defstruct (comp-limple-frame (:copier nil))
  "A LIMPLE func."
  (sp 0 :type 'fixnum
      :documentation "Current stack pointer")
  (frame nil :type 'vector
         :documentation "Meta-stack used to flat LAP"))

(defun comp-limple-frame-new-frame (size)
  "Return a clean frame of meta variables of size SIZE."
  (let ((v (make-vector size nil)))
    (cl-loop for i below size
             do (aset v i (make-comp-mvar :slot i)))
    v))

(defun comp-c-func-name (symbol-function)
  "Given SYMBOL-FUNCTION return a name suitable for the native code."
  ;; Unfortunatelly not all symbol names are valid as C function names...
  ;; Nassi's algorithm.
  (let* ((orig-name (symbol-name symbol-function))
         (crypted (cl-loop with str = (make-string (* 2 (length orig-name)) 0)
	                   for j from 0 by 2
	                   for i across orig-name
	                   for byte = (format "%x" i)
	                   do (aset str j (aref byte 0))
	                   do (aset str (1+ j) (aref byte 1))
	                   finally return str))
         (human-readable (replace-regexp-in-string
                          "-" "_" orig-name))
         (human-readable (replace-regexp-in-string
                          (rx (not (any "a-z_"))) "" human-readable)))
    (concat "F" crypted "_" human-readable)))

(defun comp-decrypt-lambda-list (x)
  "Decript lambda list X."
  (let ((rest (not (= (logand x 128) 0)))
        (mandatory (logand x 127))
        (nonrest (ash x -8)))
    (if (and (null rest)
             (< nonrest 9)) ;; SUBR_MAX_ARGS
        (make-comp-args :min mandatory
                        :max nonrest)
      (make-comp-args :min mandatory
                      :ncall-conv t))))

(defun comp-recuparate-lap (func)
  "Byte compile and recuparate LAP rapresentation for FUNC."
  ;; FIXME block timers here, otherwise we could spill the wrong LAP.
  (setf (comp-func-byte-func func)
        (byte-compile (comp-func-symbol-name func)))
  (when comp-debug
    (cl-prettyprint byte-compile-lap-output))
  (let ((lambda-list (aref (comp-func-byte-func func) 0)))
    (if (fixnump lambda-list)
        (setf (comp-func-args func)
              (comp-decrypt-lambda-list (aref (comp-func-byte-func func) 0)))
      (error "Can't native compile a non lexical scoped function")))
  (setf (comp-func-ir func) byte-compile-lap-output)
  (setf (comp-func-frame-size func) (aref (comp-func-byte-func func) 3))
  func)

(declare-function comp-init-ctxt "comp.c")
(declare-function comp-release-ctxt "comp.c")
(declare-function comp-add-func-to-ctxt "comp.c")
(declare-function comp-compile-and-load-ctxt "comp.c")

;; (defun comp-opt-call (inst)
;;   "Optimize if possible a side-effect-free call in INST."
;;   (cl-destructuring-bind (_ f &rest args) inst
;;     (when (and (member f comp-mostly-pure-funcs)
;;                (cl-every #'identity (mapcar #'comp-mvar-const-vld args)))
;;       (apply f (mapcar #'comp-mvar-constant args)))))

;; Special vars used during limplifications
(defvar comp-frame)
(defvar comp-limple)
(defvar comp-func)

(cl-defun make-comp-mvar (&key slot const-vld constant type)
  (make--comp-mvar :id (cl-incf (comp-func-limple-cnt comp-func))
                   :slot slot :const-vld const-vld :constant constant
                   :type type))

(defmacro comp-sp ()
  "Current stack pointer."
  '(comp-limple-frame-sp comp-frame))

(defmacro comp-slot-n (n)
  "Slot N into the meta-stack."
  `(aref (comp-limple-frame-frame comp-frame) ,n))

(defmacro comp-slot ()
  "Current slot into the meta-stack pointed by sp."
  '(comp-slot-n (comp-sp)))

(defmacro comp-slot-next ()
  "Slot into the meta-stack pointed by sp + 1."
  '(comp-slot-n (1+ (comp-sp))))

(defun comp-push-call (src-slot)
  "Push call SRC-SLOT into frame."
  (cl-assert src-slot)
  (cl-incf (comp-sp))
  (setf (comp-slot)
        (make-comp-mvar :slot (comp-sp)
                        :type (alist-get (cadr src-slot)
                                         comp-known-ret-types)))
  (push (list 'set (comp-slot) src-slot) comp-limple))

(defun comp-push-slot-n (n)
  "Push slot number N into frame."
  (let ((src-slot (comp-slot-n n)))
    (cl-assert src-slot)
    (cl-incf (comp-sp))
    (setf (comp-slot)
          (copy-sequence src-slot))
    (setf (comp-mvar-slot (comp-slot)) (comp-sp))
    (push (list 'set (comp-slot) src-slot) comp-limple)))

(defun comp-emit-annotation (str)
  "Emit annotation STR."
  (push `(comment ,str) comp-limple))

(defun comp-push-const (val)
  "Push VAL into frame.
VAL is known at compile time."
  (cl-incf (comp-sp))
  (setf (comp-slot) (make-comp-mvar :slot (comp-sp)
                                    :const-vld t
                                    :constant val))
  (push (list 'setimm (comp-slot) val) comp-limple))

(defun comp-push-block (bblock)
  "Push basic block BBLOCK."
  (push bblock (comp-func-blocks comp-func))
  ;; Every new block we are forced to wipe out all the frame.
  ;; This will be superseded by proper flow analysis.
  (setf (comp-limple-frame-frame comp-frame)
        (comp-limple-frame-new-frame (comp-func-frame-size comp-func)))
  (push `(block ,bblock) comp-limple))

(defun comp-pop (n)
  "Pop N elements from the meta-stack."
  (cl-decf (comp-sp) n))

(defun comp-limplify-listn (n)
  "Limplify list N."
  (comp-pop 1)
  (comp-push-call `(call Fcons ,(comp-slot-next)
                         ,(make-comp-mvar :const-vld t
                                          :constant nil)))
  (dotimes (_ (1- n))
    (comp-pop 2)
    (comp-push-call `(call Fcons
                           ,(comp-slot-next)
                           ,(comp-slot-n (+ 2 (comp-sp)))))))

(defun comp-limplify-lap-inst (inst)
  "Limplify LAP instruction INST accumulating in `comp-limple'."
  (let ((op (car inst)))
    (pcase op
      ('byte-dup
       (comp-push-slot-n (comp-sp)))
      ('byte-varref
       (comp-push-call `(call Fsymbol_value ,(make-comp-mvar
                                              :const-vld t
                                              :constant (cadr inst)))))
      ;; ('byte-varset
      ;;  (comp-push-call `(call Fsymbol_value ,(cadr inst))))
      ('byte-constant
       (comp-push-const (cadr inst)))
      ('byte-stack-ref
       (comp-push-slot-n (- (comp-sp) (cdr inst))))
      ('byte-plus
       (comp-pop 2)
       (comp-push-call `(callref Fplus 2 ,(comp-sp))))
      ('byte-car
       (comp-pop 1)
       (comp-push-call `(call Fcar ,(comp-slot))))
      ('byte-cdr
       (comp-pop 1)
       (comp-push-call `(call Fcdr ,(comp-slot))))
      ('byte-car-safe
       (comp-pop 1)
       (comp-push-call `(call Fcar_safe ,(comp-slot))))
      ('byte-cdr-safe
       (comp-pop 1)
       (comp-push-call `(call Fcdr_safe ,(comp-slot))))
      ('byte-list1
       (comp-limplify-listn 1))
      ('byte-list2
       (comp-limplify-listn 2))
      ('byte-list3
       (comp-limplify-listn 3))
      ('byte-list4
       (comp-limplify-listn 4))
      ('byte-return
       (push (list 'return (comp-slot)) comp-limple)
       `(return ,(comp-slot)))
      (_ (error "Unexpected LAP op %s" (symbol-name op))))))

(defun comp-limplify (func)
  "Given FUNC and return compute its LIMPLE ir."
  (let* ((frame-size (comp-func-frame-size func))
         (comp-func func)
         (comp-frame (make-comp-limple-frame
                      :sp -1
                      :frame (comp-limple-frame-new-frame frame-size)))
         (comp-limple ()))
    ;; Prologue
    (comp-push-block 'entry)
    (comp-emit-annotation (concat "Lisp function: "
                                  (symbol-name (comp-func-symbol-name func))))
    (cl-loop for i below (comp-args-mandatory (comp-func-args func))
             do (progn
                  (cl-incf (comp-sp))
                  (push `(setpar ,(comp-slot) ,i) comp-limple)))
    (push '(jump body) comp-limple)
    ;; Body
    (comp-push-block 'body)
    (mapc #'comp-limplify-lap-inst (comp-func-ir func))
    (setf (comp-func-ir func) (reverse comp-limple))
    ;; Prologue block must be first
    (setf (comp-func-blocks func) (reverse (comp-func-blocks func)))
    (when comp-debug
      (cl-prettyprint (comp-func-ir func)))
    func))

(defun native-compile (fun)
  "FUN is the function definition to be compiled into native code."
  (if-let ((f (symbol-function fun)))
      (progn
        (when (byte-code-function-p f)
          (error "Can't native compile an already bytecompiled function"))
        (let ((func (make-comp-func :symbol-name fun
                                    :func f
                                    :c-func-name (comp-c-func-name fun))))
          (mapc (lambda (pass)
                  (funcall pass func))
                comp-passes)
          ;; Once we have the final LIMPLE we jump into C.
          (comp-init-ctxt)
          (comp-add-func-to-ctxt func)
          (comp-compile-and-load-ctxt)
          (comp-release-ctxt)))
    (error "Trying to native compile something not a function")))

(provide 'comp)

;;; comp.el ends here