;;; -*-lisp-*-
;;;
;;; Code generation protocol
;;;
;;; (c) 2009 Straylight/Edgeware
;;;

;;;----- Licensing notice ---------------------------------------------------
;;;
;;; This file is part of the Sensble Object Design, an object system for C.
;;;
;;; SOD 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 2 of the License, or
;;; (at your option) any later version.
;;;
;;; SOD 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 SOD; if not, write to the Free Software Foundation,
;;; Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

(cl:in-package #:sod)

;;;--------------------------------------------------------------------------
;;; Temporary names.

;; Protocol.

(export 'format-temporary-name)
(defgeneric format-temporary-name (var stream)
  (:documentation
   "Write the name of a temporary variable VAR to STREAM."))

(export 'var-in-use-p)
(defgeneric var-in-use-p (var)
  (:documentation
   "Answer whether VAR is currently being used.  See `with-temporary-var'.")
  (:method (var)
    "Non-temporary variables are always in use."
    (declare (ignore var))
    t))
(defgeneric (setf var-in-use-p) (value var)
  (:documentation
   "Record whether VAR is currently being used.  See `with-temporary-var'."))

;; Root class.

(export 'temporary-name)
(defclass temporary-name ()
  ((tag :initarg :tag :reader temp-tag))
  (:documentation
   "Base class for temporary variable and argument names."))

;; Important variables.

(defparameter *temporary-index* 0
  "Index for temporary name generation.

   This is automatically reset to zero before the output functions are
   invoked to write a file.  This way, we can ensure that the same output
   file is always produced from the same input.")

(define-clear-the-decks reset-codegen-index
  (setf *temporary-index* 0))

;; Important temporary names.

(export '(*sod-ap* *sod-master-ap*))
(defparameter *sod-ap*
  (make-instance 'temporary-name :tag "sod__ap"))
(defparameter *sod-master-ap*
  (make-instance 'temporary-name :tag "sod__master_ap"))

;;;--------------------------------------------------------------------------
;;; Instructions.

;; Classes.

(export 'inst)
(defclass inst () ()
  (:documentation
   "A base class for instructions.

   An `instruction' is anything which might be useful to string into a code
   generator.  Both statements and expressions can be represented by trees of
   instructions.  The `definst' macro is a convenient way of defining new
   instructions.

   The only important protocol for instructions is output, which is achieved
   by calling `print-object' with `*print-escape*' nil.

   This doesn't really do very much, but it acts as a handy marker for
   instruction subclasses."))

(export 'inst-metric)
(defgeneric inst-metric (inst)
  (:documentation
   "Returns a `metric' describing how complicated INST is.

   The default metric of an inst node is simply 1; `inst' subclasses
   generated by `definst' (q.v.) have an automatically generated method which
   returns one plus the sum of the metrics of the node's children.

   This isn't intended to be a particularly rigorous definition.  Its purpose
   is to allow code generators to make decisions about inlining or calling
   code fairly simply.")
  (:method ((inst t))
    (declare (ignore inst))
    1)
  (:method ((inst null))
    (declare (ignore inst))
    1)
  (:method ((inst list))
    (reduce #'+ inst :key #'inst-metric)))

;; Instruction definition.

(export 'definst)
(defmacro definst (code (streamvar) args &body body)
  "Define an instruction type and describe how to output it.

   An `inst' can represent any structured piece of output syntax: a
   statement, expression or declaration, for example.  This macro defines the
   following things:

     * A class `CODE-inst' to represent the instruction.

     * Instance slots named after the ARGS, with matching keyword initargs,
       and `inst-ARG' readers.

     * A constructor `make-CODE-inst' which accepts the ARGS (in order, not
       with keywords) as arguments and returns a fresh instance.

     * A print method, which prints a diagnostic dump if `*print-escape*' is
       set, or invokes the BODY (with STREAMVAR bound to the output stream)
       otherwise.  The BODY is expected to produce target code at this
       point."

  (let ((inst-var (gensym "INST"))
	(class-name (symbolicate code '-inst))
	(keys (mapcar (lambda (arg) (intern (symbol-name arg) :keyword))
		      args)))
    `(progn
       (defclass ,class-name (inst)
	 ,(mapcar (lambda (arg key)
		    `(,arg :initarg ,key :reader ,(symbolicate 'inst- arg)))
		  args keys))
       (defun ,(symbolicate 'make- code '-inst) (,@args)
	 (make-instance ',class-name ,@(mappend #'list keys args)))
       (defmethod inst-metric ((,inst-var ,class-name))
	 (with-slots (,@args) ,inst-var
	   (+ 1 ,@(mapcar (lambda (arg) `(inst-metric ,arg)) args))))
       (defmethod print-object ((,inst-var ,class-name) ,streamvar)
	 (with-slots (,@args) ,inst-var
	   (if *print-escape*
	       (print-unreadable-object (,inst-var ,streamvar :type t)
		 (format stream "~@<~@{~S ~@_~S~^ ~_~}~:>"
			 ,@(mappend #'list keys args)))
	       (progn ,@body)))))))

;; Important instruction classes.

(export '(block-inst make-block-inst var-inst make-var-inst
	  function-inst make-function-inst set-inst make-set-inst
	  return-inst make-return-inst expr-inst make-expr-inst
	  inst-decls inst-body inst-name inst-type inst-init inst-var
	  inst-expr))

(definst var (stream) (name type init)
  (pprint-c-type type stream name)
  (when init
    (format stream " = ~A" init)))
(definst set (stream) (var expr)
  (format stream "~@<~A = ~@_~2I~A;~:>" var expr))
(definst return (stream) (expr)
  (format stream "return~@[ (~A)~];" expr))
(definst expr (stream) (expr)
  (format stream "~A;" expr))
(definst block (stream) (decls body)
  (format stream "{~:@_~@<  ~2I~@[~{~A;~:@_~}~:@_~]~{~A~^~:@_~}~:>~:@_}"
	  decls body))
(definst function (stream) (name type body)
  (pprint-logical-block (stream nil)
    (princ "static " stream)
    (pprint-c-type type stream name)
    (format stream "~:@_~A~:@_~:@_" body)))

;; Formatting utilities.

(defun format-compound-statement* (stream child morep thunk)
  "Underlying function for `format-compound-statement'."
  (cond ((typep child 'block-inst)
	 (funcall thunk stream)
	 (write-char #\space stream)
	 (princ child stream)
	 (when morep (write-char #\space stream)))
	(t
	 (pprint-logical-block (stream nil)
	   (funcall thunk stream)
	   (write-char #\space stream)
	   (pprint-indent :block 2 stream)
	   (pprint-newline :linear stream)
	   (princ child stream)
	   (pprint-indent :block 0 stream)
	   (case morep
	     (:space
	      (write-char #\space stream)
	      (pprint-newline :linear stream))
	     ((t)
	      (pprint-newline :mandatory stream)))))))

(export 'format-compound-statement)
(defmacro format-compound-statement
    ((stream child &optional morep) &body body)
  "Format a compound statement to STREAM.

   The introductory material is printed by BODY.  The CHILD is formatted
   properly according to whether it's a `block-inst'.  If MOREP is true, then
   allow for more stuff following the child."
  `(format-compound-statement* ,stream ,child ,morep
			       (lambda (,stream) ,@body)))

;;;--------------------------------------------------------------------------
;;; Code generation.

;; Accessors.

(export 'codegen-functions)
(defgeneric codegen-functions (codegen)
  (:documentation
   "Return the list of `function-inst's of completed functions."))

(export 'ensure-var)
(defgeneric ensure-var (codegen name type &optional init)
  (:documentation
   "Add a variable to CODEGEN's list.

   The variable is called NAME (which should be comparable using `equal' and
   print to an identifier) and has the given TYPE.  If INIT is present and
   non-nil it is an expression `inst' used to provide the variable with an
   initial value."))

(export '(emit-inst emit-insts))
(defgeneric emit-inst (codegen inst)
  (:documentation
   "Add INST to the end of CODEGEN's list of instructions."))
(defgeneric emit-insts (codegen insts)
  (:documentation
   "Add a list of INSTS to the end of CODEGEN's list of instructions.")
  (:method (codegen insts)
    (dolist (inst insts) (emit-inst codegen inst))))

(export 'codegen-push)
(defgeneric codegen-push (codegen)
  (:documentation
   "Pushes the current code generation state onto a stack.

   The state consists of the accumulated variables and instructions."))

(export 'codegen-pop)
(defgeneric codegen-pop (codegen)
  (:documentation
   "Pops a saved state off of the CODEGEN's stack.

   Returns the newly accumulated variables and instructions as lists, as
   separate values."))

(export 'codegen-add-function)
(defgeneric codegen-add-function (codegen function)
  (:documentation
   "Adds a function to CODEGEN's list.

   Actually, we're not picky: FUNCTION can be any kind of object that you're
   willing to find in the list returned by `codegen-functions'."))

(export 'temporary-var)
(defgeneric temporary-var (codegen type)
  (:documentation
   "Return the name of a temporary variable.

   The temporary variable will have the given TYPE, and will be marked
   in-use.  You should clear the in-use flag explicitly when you've finished
   with the variable -- or, better, use `with-temporary-var' to do the
   cleanup automatically."))

(export 'codegen-build-function)
(defun codegen-build-function (codegen name type vars insts)
  "Build a function and add it to CODEGEN's list.

   Returns the function's name."
  (codegen-add-function codegen
			(make-function-inst name type
					    (make-block-inst vars insts)))
  name)

(export 'codegen-pop-block)
(defgeneric codegen-pop-block (codegen)
  (:documentation
   "Makes a block (`block-inst') out of the completed code in CODEGEN.")
  (:method (codegen)
    (multiple-value-bind (vars insts) (codegen-pop codegen)
      (make-block-inst vars insts))))

(export 'codegen-pop-function)
(defgeneric codegen-pop-function (codegen name type)
  (:documentation
   "Makes a function out of the completed code in CODEGEN.

   The NAME can be any object you like.  The TYPE should be a function type
   object which includes argument names.  The return value is the NAME.")
  (:method (codegen name type)
    (multiple-value-bind (vars insts) (codegen-pop codegen)
      (codegen-build-function codegen name type vars insts))))

(export 'with-temporary-var)
(defmacro with-temporary-var ((codegen var type) &body body)
  "Evaluate BODY with VAR bound to a temporary variable name.

   During BODY, VAR will be marked in-use; when BODY ends, VAR will be marked
   available for re-use."
  `(let ((,var (temporary-var ,codegen ,type)))
     (unwind-protect
	  (progn ,@body)
       (setf (var-in-use-p ,var) nil))))

;;;--------------------------------------------------------------------------
;;; Code generation idioms.

(export 'deliver-expr)
(defun deliver-expr (codegen target expr)
  "Emit code to deliver the value of EXPR to the TARGET.

   The TARGET may be one of the following.

     * `:void', indicating that the value is to be discarded.  The expression
       will still be evaluated.

     * `:void-return', indicating that the value is to be discarded (as for
       `:void') and furthermore a `return' from the current function should
       be forced after computing the value.

     * `:return', indicating that the value is to be returned from the
       current function.

     * A variable name, indicating that the value is to be stored in the
       variable.

   In the cases of `:return', `:void' and `:void-return' targets, it is valid
   for EXPR to be nil; this signifies that no computation needs to be
   performed.  Variable-name targets require an expression."

  (case target
    (:return (emit-inst codegen (make-return-inst expr)))
    (:void (when expr (emit-inst codegen (make-expr-inst expr))))
    (:void-return (when expr (emit-inst codegen (make-expr-inst expr)))
		  (emit-inst codegen (make-return-inst nil)))
    (t (emit-inst codegen (make-set-inst target expr)))))

(export 'convert-stmts)
(defun convert-stmts (codegen target type func)
  "Invoke FUNC to deliver a value to a non-`:return' target.

   FUNC is a function which accepts a single argument, a non-`:return'
   target, and generates statements which deliver a value (see
   `deliver-expr') of the specified TYPE to this target.  In general, the
   generated code will have the form

     setup instructions...
     (deliver-expr CODEGEN TARGET (compute value...))
     cleanup instructions...

   where the cleanup instructions are essential to the proper working of the
   generated program.

   The `convert-stmts' function will call FUNC to generate code, and arrange
   that its value is correctly delivered to TARGET, regardless of what the
   TARGET is -- i.e., it lifts the restriction to non-`:return' targets.  It
   does this by inventing a new temporary variable."

  (case target
    (:return (with-temporary-var (codegen var type)
	       (funcall func var)
	       (deliver-expr codegen target var)))
    (:void-return (funcall func :void)
		  (emit-inst codegen (make-return-inst nil)))
    (t (funcall func target))))

;;;----- That's all, folks --------------------------------------------------