;;;; This file contains the code that finds the initial components and
;;;; DFO, and recomputes the DFO if it is invalidated.

;;;; This software is part of the SBCL system. See the README file for
;;;; more information.
;;;;
;;;; This software is derived from the CMU CL system, which was
;;;; written at Carnegie Mellon University and released into the
;;;; public domain. The software is in the public domain and is
;;;; provided with absolutely no warranty. See the COPYING and CREDITS
;;;; files for more information.

(in-package "SB!C")

;;; Find the DFO for a component, deleting any unreached blocks and
;;; merging any other components we reach. We repeatedly iterate over
;;; the entry points, since new ones may show up during the walk.
(declaim (ftype (function (component) (values)) find-dfo))
(defun find-dfo (component)
  (clear-flags component)
  (setf (component-reanalyze component) nil)
  (let ((head (component-head component)))
    (do ()
	((dolist (ep (block-succ head) t)
	   (unless (block-flag ep)
	     (find-dfo-aux ep head component)
	     (return nil))))))

  (let ((num 0))
    (declare (fixnum num))
    (do-blocks-backwards (block component :both)
      (if (block-flag block)
	  (setf (block-number block) (incf num))
	  (setf (block-delete-p block) t)))
    (do-blocks (block component)
      (unless (block-flag block)
	(delete-block block))))
  (values))

;;; Move all the code and entry points from OLD to NEW. The code in
;;; OLD is inserted at the head of NEW. This is also called during LET
;;; conversion when we are about in insert the body of a LET in a
;;; different component. [A local call can be to a different component
;;; before FIND-INITIAL-DFO runs.]
(declaim (ftype (function (component component) (values)) join-components))
(defun join-components (new old)
  (aver (eq (component-kind new) (component-kind old)))
  (let ((old-head (component-head old))
	(old-tail (component-tail old))
	(head (component-head new))
	(tail (component-tail new)))

    (do-blocks (block old)
      (setf (block-flag block) nil)
      (setf (block-component block) new))

    (let ((old-next (block-next old-head))
	  (old-last (block-prev old-tail))
	  (next (block-next head)))
      (unless (eq old-next old-tail)
	(setf (block-next head) old-next)
	(setf (block-prev old-next) head)
	
	(setf (block-prev next) old-last)
	(setf (block-next old-last) next))

      (setf (block-next old-head) old-tail)
      (setf (block-prev old-tail) old-head))

    (setf (component-lambdas new)
	  (nconc (component-lambdas old) (component-lambdas new)))
    (setf (component-lambdas old) ())
    (setf (component-new-functions new)
	  (nconc (component-new-functions old) (component-new-functions new)))
    (setf (component-new-functions old) ())

    (dolist (xp (block-pred old-tail))
      (unlink-blocks xp old-tail)
      (link-blocks xp tail))
    (dolist (ep (block-succ old-head))
      (unlink-blocks old-head ep)
      (link-blocks head ep)))
  (values))

;;; Do a depth-first walk from BLOCK, inserting ourself in the DFO
;;; after HEAD. If we somehow find ourselves in another component,
;;; then we join that component to our component.
(declaim (ftype (function (cblock cblock component) (values)) find-dfo-aux))
(defun find-dfo-aux (block head component)
  (unless (eq (block-component block) component)
    (join-components component (block-component block)))
	
  (unless (block-flag block)
    (setf (block-flag block) t)
    (dolist (succ (block-succ block))
      (find-dfo-aux succ head component))

    (remove-from-dfo block)
    (add-to-dfo block head))
  (values))

;;; This function is called on each block by FIND-INITIAL-DFO-AUX
;;; before it walks the successors. It looks at the home lambda's bind
;;; block to see whether that block is in some other component:

;;; -- If the block is in the initial component, then do
;;;    DFO-WALK-CALL-GRAPH on the home function to move it
;;;    into COMPONENT.
;;; -- If the block is in some other component, join COMPONENT into
;;;    it and return that component.
;;; -- If the home function is deleted, do nothing. BLOCK must
;;;    eventually be discovered to be unreachable as well. This can
;;;    happen when we have a NLX into a function with no references.
;;;    The escape function still has refs (in the deleted function).
;;;
;;; This ensures that all the blocks in a given environment will be in
;;; the same component, even when they might not seem reachable from
;;; the environment entry. Consider the case of code that is only
;;; reachable from a non-local exit.
(defun walk-home-call-graph (block component)
  (declare (type cblock block) (type component component))
  (let ((home (block-home-lambda block)))
    (if (eq (functional-kind home) :deleted)
	component
	(let* ((bind-block (node-block (lambda-bind home)))
	       (home-component (block-component bind-block)))
	  (cond ((eq (component-kind home-component) :initial)
		 (dfo-walk-call-graph home component))
		((eq home-component component)
		 component)
		(t
		 (join-components home-component component)
		 home-component))))))

;;; This is somewhat similar to FIND-DFO-AUX, except that it merges
;;; the current component with any strange component, rather than the
;;; other way around. This is more efficient in the common case where
;;; the current component doesn't have much stuff in it.
;;;
;;; We return the current component as a result, allowing the caller
;;; to detect when the old current component has been merged with
;;; another.
;;;
;;; We walk blocks in initial components as though they were already
;;; in the current component, moving them to the current component in
;;; the process. The blocks are inserted at the head of the current
;;; component.
(defun find-initial-dfo-aux (block component)
  (declare (type cblock block) (type component component))
  (let ((this (block-component block)))
    (cond
     ((not (or (eq this component)
	       (eq (component-kind this) :initial)))
      (join-components this component)
      this)
     ((block-flag block) component)
     (t
      (setf (block-flag block) t)
      (let ((current (walk-home-call-graph block component)))
	(dolist (succ (block-succ block))
	  (setq current (find-initial-dfo-aux succ current)))
	
	(remove-from-dfo block)
	(add-to-dfo block (component-head current))
	current)))))

;;; Return a list of all the home lambdas that reference FUN (may
;;; contain duplications).
;;;
;;; References to functions which local call analysis could not (or
;;; were chosen not) to local call convert will appear as references
;;; to XEP lambdas. We can ignore references to XEPs that appear in
;;; :TOP-LEVEL components, since environment analysis goes to special
;;; effort to allow closing over of values from a separate top-level
;;; component. (And now that HAS-EXTERNAL-REFERENCES-P-ness
;;; generalizes :TOP-LEVEL-ness, we ignore those too.) All other
;;; references must cause components to be joined.
;;;
;;; References in deleted functions are also ignored, since this code
;;; will be deleted eventually.
(defun find-reference-functions (fun)
  (collect ((res))
    (dolist (ref (leaf-refs fun))
      (let* ((home (node-home-lambda ref))
	     (home-kind (functional-kind home))
	     (home-externally-visible-p
	      (or (eq home-kind :top-level)
		  (functional-has-external-references-p home))))
	(unless (or (and home-externally-visible-p
			 (eq (functional-kind fun) :external))
		    (eq home-kind :deleted))
	  (res home))))
    (res)))

;;; Move the code for FUN and all functions called by it into
;;; COMPONENT. If FUN is already in COMPONENT, then we just return
;;; that component.
;;;
;;; If the function is in an initial component, then we move its head
;;; and tail to COMPONENT and add it to COMPONENT's lambdas. It is
;;; harmless to move the tail (even though the return might be
;;; unreachable) because if the return is unreachable it (and its
;;; successor link) will be deleted in the post-deletion pass.
;;;
;;; We then do a FIND-DFO-AUX starting at the head of FUN. If this
;;; flow-graph walk encounters another component (which can only
;;; happen due to a non-local exit), then we move code into that
;;; component instead. We then recurse on all functions called from
;;; FUN, moving code into whichever component the preceding call
;;; returned.
;;;
;;; If FUN is in the initial component, but the BLOCK-FLAG is set in
;;; the bind block, then we just return COMPONENT, since we must have
;;; already reached this function in the current walk (or the
;;; component would have been changed).
;;;
;;; If the function is an XEP, then we also walk all functions that
;;; contain references to the XEP. This is done so that environment
;;; analysis doesn't need to cross component boundaries. This also
;;; ensures that conversion of a full call to a local call won't
;;; result in a need to join components, since the components will
;;; already be one.
(defun dfo-walk-call-graph (fun component)
  (declare (type clambda fun) (type component component))
  (let* ((bind-block (node-block (lambda-bind fun)))
	 (this (block-component bind-block))
	 (return (lambda-return fun)))
    (cond
     ((eq this component) component)
     ((not (eq (component-kind this) :initial))
      (join-components this component)
      this)
     ((block-flag bind-block)
      component)
     (t
      (push fun (component-lambdas component))
      (setf (component-lambdas this)
	    (delete fun (component-lambdas this)))
      (link-blocks (component-head component) bind-block)
      (unlink-blocks (component-head this) bind-block)
      (when return
	(let ((return-block (node-block return)))
	  (link-blocks return-block (component-tail component))
	  (unlink-blocks return-block (component-tail this))))
      (let ((calls (if (eq (functional-kind fun) :external)
		       (append (find-reference-functions fun)
			       (lambda-calls fun))
		       (lambda-calls fun))))
	(do ((res (find-initial-dfo-aux bind-block component)
		  (dfo-walk-call-graph (first funs) res))
	     (funs calls (rest funs)))
	    ((null funs) res)
	  (declare (type component res))))))))

;;; Return true if FUN is either an XEP or has EXITS to some of its
;;; ENTRIES.
(defun has-xep-or-nlx (fun)
  (declare (type clambda fun))
  (or (eq (functional-kind fun) :external)
      (let ((entries (lambda-entries fun)))
	(and entries
	     (find-if #'entry-exits entries)))))

;;; Compute the result of FIND-INITIAL-DFO given the list of all
;;; resulting components. Components with a :TOP-LEVEL lambda, but no
;;; normal XEPs or potential non-local exits are marked as :TOP-LEVEL.
;;; If there is a :TOP-LEVEL lambda, and also a normal XEP, then we
;;; treat the component as normal, but also return such components in
;;; a list as the third value. Components with no entry of any sort
;;; are deleted.
(defun find-top-level-components (components)
  (declare (list components))
  (collect ((real)
	    (top)
	    (real-top))
    (dolist (com components)
      (unless (eq (block-next (component-head com)) (component-tail com))
	(let* ((funs (component-lambdas com))
	       (has-top (find :top-level funs :key #'functional-kind))
	       (has-external-references
		(some #'functional-has-external-references-p funs)))
	  (cond (;; The FUNCTIONAL-HAS-EXTERNAL-REFERENCES-P concept
		 ;; is newer than the rest of this function, and
		 ;; doesn't really seem to fit into its mindset. Here
		 ;; we mark components which contain such FUNCTIONs
		 ;; them as :COMPLEX-TOP-LEVEL, since they do get
		 ;; executed at run time, and since it's not valid to
		 ;; delete them just because they don't have any
		 ;; references from pure :TOP-LEVEL components. -- WHN
		 has-external-references
		 (setf (component-kind com) :complex-top-level)
		 (real com)
		 (real-top com))
		((or (some #'has-xep-or-nlx funs)
		     (and has-top (rest funs)))
		 (setf (component-name com) (find-component-name com))
		 (real com)
		 (when has-top
		   (setf (component-kind com) :complex-top-level)
		   (real-top com)))
		(has-top
		 (setf (component-kind com) :top-level)
		 (setf (component-name com) "top-level form")
		 (top com))
		(t
		 (delete-component com))))))

    (values (real) (top) (real-top))))

;;; Given a list of top-level lambdas, return three lists of
;;; components representing the actual component division:
;;;  1. the non-top-level components,
;;;  2. and the second is the top-level components, and
;;;  3. Components in [1] that also have a top-level lambda.
;;;
;;; We assign the DFO for each component, and delete any unreachable
;;; blocks. We assume that the Flags have already been cleared.
;;;
;;; We iterate over the lambdas in each initial component, trying to
;;; put each function in its own component, but joining it to an
;;; existing component if we find that there are references between
;;; them. Any code that is left in an initial component must be
;;; unreachable, so we can delete it. Stray links to the initial
;;; component tail (due NIL function terminated blocks) are moved to
;;; the appropriate newc component tail.
;;;
;;; When we are done, we assign DFNs and call
;;; FIND-TOP-LEVEL-COMPONENTS to pull out top-level code.
(defun find-initial-dfo (lambdas)
  (declare (list lambdas))
  (collect ((components))
    (let ((new (make-empty-component)))
      (dolist (tll lambdas)
	(let ((component (block-component (node-block (lambda-bind tll)))))
	  (dolist (fun (component-lambdas component))
	    (aver (member (functional-kind fun)
			  '(:optional :external :top-level nil :escape
				      :cleanup)))
	    (let ((res (dfo-walk-call-graph fun new)))
	      (when (eq res new)
		(components new)
		(setq new (make-empty-component)))))
	  (when (eq (component-kind component) :initial)
	    (aver (null (component-lambdas component)))
	    (let ((tail (component-tail component)))
	      (dolist (pred (block-pred tail))
		(let ((pred-component (block-component pred)))
		  (unless (eq pred-component component)
		    (unlink-blocks pred tail)
		    (link-blocks pred (component-tail pred-component))))))
	    (delete-component component)))))

    (dolist (com (components))
      (let ((num 0))
	(declare (fixnum num))
	(do-blocks-backwards (block com :both)
	  (setf (block-number block) (incf num)))))

    (find-top-level-components (components))))

;;; Insert the code in LAMBDA at the end of RESULT-LAMBDA.
(defun merge-1-tl-lambda (result-lambda lambda)
  (declare (type clambda result-lambda lambda))

  ;; Delete the lambda, and combine the LETs and entries.
  (setf (functional-kind lambda) :deleted)
  (dolist (let (lambda-lets lambda))
    (setf (lambda-home let) result-lambda)
    (setf (lambda-physenv let) (lambda-physenv result-lambda))
    (push let (lambda-lets result-lambda)))
  (setf (lambda-entries result-lambda)
	(nconc (lambda-entries result-lambda)
	       (lambda-entries lambda)))

  (let* ((bind (lambda-bind lambda))
	 (bind-block (node-block bind))
	 (component (block-component bind-block))
	 (result-component
	  (block-component (node-block (lambda-bind result-lambda))))
	 (result-return-block (node-block (lambda-return result-lambda))))

    ;; Move blocks into the new COMPONENT, and move any nodes directly
    ;; in the old LAMBDA into the new one (with LETs implicitly moved
    ;; by changing their home.)
    (do-blocks (block component)
      (do-nodes (node cont block)
	(let ((lexenv (node-lexenv node)))
	  (when (eq (lexenv-lambda lexenv) lambda)
	    (setf (lexenv-lambda lexenv) result-lambda))))
      (setf (block-component block) result-component))

    ;; Splice the blocks into the new DFO, and unlink them from the
    ;; old component head and tail. Non-return blocks that jump to the
    ;; tail (NIL-returning calls) are switched to go to the new tail.
    (let* ((head (component-head component))
	   (first (block-next head))
	   (tail (component-tail component))
	   (last (block-prev tail))
	   (prev (block-prev result-return-block)))
      (setf (block-next prev) first)
      (setf (block-prev first) prev)
      (setf (block-next last) result-return-block)
      (setf (block-prev result-return-block) last)
      (dolist (succ (block-succ head))
	(unlink-blocks head succ))
      (dolist (pred (block-pred tail))
	(unlink-blocks pred tail)
	(let ((last (block-last pred)))
	  (unless (return-p last)
	    (aver (basic-combination-p last))
	    (link-blocks pred (component-tail result-component))))))

    (let ((lambdas (component-lambdas component)))
      (aver (and (null (rest lambdas))
		 (eq (first lambdas) lambda))))

    ;; Switch the end of the code from the return block to the start of
    ;; the next chunk.
    (dolist (pred (block-pred result-return-block))
      (unlink-blocks pred result-return-block)
      (link-blocks pred bind-block))
    (unlink-node bind)

    ;; If there is a return, then delete it (making the preceding node
    ;; the last node) and link the block to the result return. There
    ;; is always a preceding REF NIL node in top-level lambdas.
    (let ((return (lambda-return lambda)))
      (when return
	(let ((return-block (node-block return))
	      (result (return-result return)))
	  (setf (block-last return-block) (continuation-use result))
	  (flush-dest result)
	  (delete-continuation result)
	  (link-blocks return-block result-return-block))))))

;;; Given a non-empty list of top-level LAMBDAs, smash them into a
;;; top-level lambda and component, returning these as values. We use
;;; the first lambda and its component, putting the other code in that
;;; component and deleting the other lambdas.
(defun merge-top-level-lambdas (lambdas)
  (declare (cons lambdas))
  (let* ((result-lambda (first lambdas))
	 (result-return (lambda-return result-lambda)))
    (cond
     (result-return

      ;; Make sure the result's return node starts a block so that we
      ;; can splice code in before it.
      (let ((prev (node-prev
		   (continuation-use
		    (return-result result-return)))))
	(when (continuation-use prev)
	  (node-ends-block (continuation-use prev)))
	(do-uses (use prev)
	  (let ((new (make-continuation)))
	    (delete-continuation-use use)
	    (add-continuation-use use new))))

      (dolist (lambda (rest lambdas))
	(merge-1-tl-lambda result-lambda lambda)))
     (t
      (dolist (lambda (rest lambdas))
	(setf (functional-entry-function lambda) nil)
	(delete-component
	 (block-component
	  (node-block (lambda-bind lambda)))))))

    (values (block-component (node-block (lambda-bind result-lambda)))
	    result-lambda)))