#| -*-Scheme-*-

Copyright (C) 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994,
    1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
    2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016,
    2017, 2018, 2019 Massachusetts Institute of Technology

This file is part of MIT/GNU Scheme.

MIT/GNU Scheme 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.

MIT/GNU Scheme 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 MIT/GNU Scheme; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301,
USA.

|#

;;;; LAP linearizer
;;; package: (compiler lap-syntaxer linearizer)

(declare (usual-integrations))

(define (bblock-linearize-lap bblock queue-continuations!)
  (define (linearize-bblock bblock)
    (LAP ,@(linearize-bblock-1 bblock)
	 ,@(linearize-next bblock)))

  (define (linearize-bblock-1 bblock)
    (node-mark! bblock)
    (queue-continuations! bblock)
    (if (and (not (bblock-label bblock))
	     (let loop ((bblock bblock))
	       (or (node-previous>1? bblock)
		   (and (node-previous=1? bblock)
			(let ((previous (node-previous-first bblock)))
			  (and (sblock? previous)
			       (null? (bblock-instructions previous))
			       (loop previous)))))))
	(bblock-label! bblock))
    (let ((kernel
	   (lambda ()
	     (bblock-instructions bblock))))
      (if (bblock-label bblock)
	  (LAP ,@(lap:make-label-statement (bblock-label bblock)) ,@(kernel))
	  (kernel))))

  (define (linearize-next bblock)
    (if (sblock? bblock)
	(let ((next (find-next (snode-next bblock))))
	  (if next
	      (linearize-sblock-next next (bblock-label next))
	      (let ((bblock (sblock-continuation bblock)))
		(if (and bblock (not (node-marked? bblock)))
		    (linearize-bblock bblock)
		    (LAP)))))
	(linearize-pblock
	 bblock
	 (find-next (pnode-consequent bblock))
	 (find-next (pnode-alternative bblock)))))

  (define (linearize-sblock-next bblock label)
    (if (node-marked? bblock)
	(lap:make-unconditional-branch label)
	(linearize-bblock bblock)))

  (define (linearize-pblock pblock cn an)
    (if (node-marked? cn)
	(if (node-marked? an)
	    (heed-preference pblock cn an
	      (lambda (generator cn an)
		(LAP ,@(generator (bblock-label cn))
		     ,@(lap:make-unconditional-branch (bblock-label an)))))
	    (LAP ,@((pblock-consequent-lap-generator pblock)
		    (bblock-label cn))
		 ,@(linearize-bblock an)))
	(if (node-marked? an)
	    (LAP ,@((pblock-alternative-lap-generator pblock)
		    (bblock-label an))
		 ,@(linearize-bblock cn))
	    (linearize-pblock-1 pblock cn an))))

  (define (linearize-pblock-1 pblock cn an)
    (let ((finish
	   (lambda (generator cn an)
	     (let ((clabel (bblock-label! cn))
		   (alternative (linearize-bblock an)))
	       (LAP ,@(generator clabel)
		    ,@alternative
		    ,@(if (node-marked? cn)
			  (LAP)
			  (linearize-bblock cn)))))))
      (let ((consequent-first
	     (lambda ()
	       (finish (pblock-alternative-lap-generator pblock) an cn)))
	    (alternative-first
	     (lambda ()
	       (finish (pblock-consequent-lap-generator pblock) cn an)))
	    (unspecial
	     (lambda ()
	       (heed-preference pblock cn an finish)))
	    (diamond
	     (lambda ()
	       (let ((jlabel (generate-label)))
		 (heed-preference pblock cn an
		   (lambda (generator cn an)
		     (let ((clabel (bblock-label! cn)))
		       (let ((consequent (linearize-bblock-1 cn))
			     (alternative (linearize-bblock-1 an)))
			 (LAP ,@(generator clabel)
			      ,@alternative
			      ,@(lap:make-unconditional-branch jlabel)
			      ,@consequent
			      ,@(lap:make-label-statement jlabel)
			      ,@(linearize-next cn))))))))))
	(cond ((eq? cn an)
	       ;;(warn "bblock-linearize-lap: Identical branches" pblock)
	       (unspecial))
	      ((sblock? cn)
	       (let ((cnn (find-next (snode-next cn))))
		 (cond ((eq? cnn an)
			(consequent-first))
		       ((sblock? an)
			(let ((ann (find-next (snode-next an))))
			  (cond ((eq? ann cn)
				 (alternative-first))
				((not cnn)
				 (if ann
				     (consequent-first)
				     (if (null? (bblock-continuations cn))
					 (if (null? (bblock-continuations an))
					     (unspecial)
					     (consequent-first))
					 (if (null? (bblock-continuations an))
					     (alternative-first)
					     (unspecial)))))
				((not ann)
				 (alternative-first))
				((eq? cnn ann)
				 (diamond))
				(else
				 (unspecial)))))
		       ((not cnn)
			(consequent-first))
		       (else
			(unspecial)))))
	      ((and (sblock? an)
		    (let ((ann (find-next (snode-next an))))
		      (or (not ann)
			  (eq? ann cn))))
	       (alternative-first))
	      (else
	       (unspecial))))))

  (define (heed-preference pblock cn an finish)
    (if (eq? 'CONSEQUENT (pnode/preferred-branch pblock))
	(finish (pblock-alternative-lap-generator pblock) an cn)
	(finish (pblock-consequent-lap-generator pblock) cn an)))

  (define (find-next bblock)
    (let loop ((bblock bblock) (previous false))
      (cond ((not bblock)
	     previous)
	    ((and (sblock? bblock)
		  (null? (bblock-instructions bblock)))
	     (loop (snode-next bblock) bblock))
	    (else
	     bblock))))

  (linearize-bblock bblock))

(define-integrable (set-current-branches! consequent alternative)
  (set-pblock-consequent-lap-generator! *current-bblock* consequent)
  (set-pblock-alternative-lap-generator! *current-bblock* alternative))

(define *end-of-block-code*)

(define-structure (extra-code-block
		   (conc-name extra-code-block/)
		   (constructor extra-code-block/make
				(name constraint xtra)))
  (name false read-only true)
  (constraint false read-only true)
  (code (LAP) read-only false)
  (xtra false read-only false))

(define linearize-lap
  (make-linearizer bblock-linearize-lap
    (lambda () (LAP))
    (lambda (x y) (LAP ,@x ,@y))
    (lambda (linearized-lap)
      (let ((end-code *end-of-block-code*))
	(set! *end-of-block-code* '())
	(LAP ,@linearized-lap
	     ,@(let process ((end-code end-code))
		 (if (null? end-code)
		     (LAP)
		     (LAP ,@(extra-code-block/code (car end-code))
			  ,@(process (cdr end-code))))))))))

(define (find-extra-code-block name)
  (let loop ((end-code *end-of-block-code*))
    (cond ((null? end-code) false)
	  ((eq? name (extra-code-block/name (car end-code)))
	   (car end-code))
	  (else
	   (loop (cdr end-code))))))

(define (declare-extra-code-block! name constraint xtra)
  (if (find-extra-code-block name)
      (error "declare-extra-code-block!: Multiply defined block"
	     name)
      (let ((new (extra-code-block/make name constraint xtra))
	    (all *end-of-block-code*))

	(define (constraint-violation new old)
	  (error "declare-extra-code-block!: Inconsistent constraints"
		 new old))

	(case constraint
	  ((FIRST)
	   (if (and (not (null? all))
		    (eq? 'FIRST
			 (extra-code-block/constraint (car all))))
	       (constraint-violation new (car all)))
	   (set! *end-of-block-code* (cons new all)))
	  ((ANYWHERE)
	   (if (or (null? all)
		   (not (eq? 'FIRST
			     (extra-code-block/constraint (car all)))))
	       (set! *end-of-block-code* (cons new all))
	       (set-cdr! all (cons new (cdr all)))))
	  ((LAST)
	   (if (null? all)
	       (set! *end-of-block-code* (list new))
	       (let* ((lp (last-pair all))
		      (old (car lp)))
		 (if (eq? 'LAST (extra-code-block/constraint old))
		     (constraint-violation new old))
		 (set-cdr! lp (cons new '())))))
	  (else
	   (error "declare-extra-code-block!: Unknown constraint"
		  constraint)))
	new)))

(define (add-extra-code! block new-code)
  (set-extra-code-block/code!
   block
   (LAP ,@(extra-code-block/code block)
	,@new-code)))

(define (add-end-of-block-code! code-thunk)
  (add-extra-code!
   (or (find-extra-code-block 'END-OF-BLOCK)
       (declare-extra-code-block! 'END-OF-BLOCK 'ANYWHERE false))
   (code-thunk)))