#| -*-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, 2020 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.

|#

;;;; Argument Ordering Analysis

(declare (usual-integrations))

;;;; Procedure parameter analysis
#|

A procedure is eligible for having its parameters be placed in
registers (i.e. the procedure is "registerizable") if the procedure
will be inlined and the frame reuse routine has not tried to overwrite
anything in the stack frame of this procedure or the stack frame
associated with any ancestors of this procedure's block.

Assuming that a procedure is registerizable, the parameter analysis
phase determines which of it's parameters will indeed be passed in
registers.

A parameter will be passed in a register if all references to that
parameter in the procedure occur before any calls to complex
procedures. A complex procedure is essentially a non-inlined,
non-open-coded procedure. Additionally, we must check to make sure
that there are no references to the parameter in any closures or
descendent blocks. Note that inlined and open-coded procedures that
are called within the analysed procedure are considered to be part of
that procedure.

At certain times (when we hit an as yet unordered parallel) we have
the opportunity to suggest an ordering of subproblems for a particular
parallel. We take that opportunity to request an ordering which would
place a reference to a parameter before any calls to complex procedures.
The order-parallel! procedure is free to ignore our suggestions.

A major deficit with the current scheme is the restriction on
registerizable procedures caused by the frame reuse stuff. The frame
reuse code is very aggressive and consequently there are very few
occasions where we can in fact place parameters in registers. The
problem is that the frame reuse code needs to know the stack layout,
but the placing of parameters in registers affects the use of the
stack. And because the parameter analysis code may call the subproblem
ordering code which may call the frame reuse code, we have a very
tricky timing problem. The correct solution may be to use a relaxation
technique and iterate the subproblem ordering so that we can put more
parameters in registers.

|#

(define (parameter-analysis procedure)
  (fluid-let ((*inlined-procedures* '()))
    (let ((interesting-parameters
	   (filter interesting-variable?
		   (procedure-required procedure))))
      (if interesting-parameters
	  (let ((registerizable-parameters
		 (with-new-node-marks
		  (lambda ()
		    (walk-node-for-search
		     (procedure-entry-node procedure))))))
	    ;; We have to check here if this procedure's block layout
	    ;; has been frozen by the frame reuse stuff which may
	    ;; have been called due to a call to order-parallel!
	    (if (block-layout-frozen? (procedure-block procedure))
		'()
		(eq-set-difference
		 (eq-set-difference interesting-parameters
				    registerizable-parameters)
		 (bad-free-variables procedure))))
	  '()))))

(define (walk-node-for-search node)
  (if (and node
	   (or (node-marked? node)
	       (begin
		 (node-mark! node)
		 (not (node-previous>1? node)))))
      (or (node/bad-variables node)
	  (cond ((and (application? node)
		      (application/combination? node)
		      (not (combination/simple-inline? node))
		      (not (let ((operator
				  (rvalue-known-value
				   (application-operator node))))
			     (and operator
				  (rvalue/procedure? operator)
				  (procedure-inline-code? operator)))))
		 (walk-next node walk-node-for-variables))
		((parallel? node)
		 (walk-node-for-search
		  (order-parallel!
		   node
		   (let ((subproblems (parallel-subproblems node)))
		     (if (every subproblem-simple? subproblems)
			 false
			 (complex-parallel-constraints
			  subproblems
			  (walk-next node walk-node-for-variables)))))))
		(else
		 (walk-next node walk-node-for-search))))
      '()))

(define (walk-next node walker)
  (cond ((application? node)
	 (case (application-type node)
	   ((COMBINATION)
	    (let ((operator (rvalue-known-value (application-operator node))))
	      (if (and operator
		       (rvalue/procedure? operator)
		       (procedure-inline-code? operator))
		  (begin
		    (set! *inlined-procedures*
			  (cons operator *inlined-procedures*))
		    (walker (procedure-entry-node operator)))
		  (walk-continuation (combination/continuation node) walker))))
	   ((RETURN)
	    (walk-continuation (return/operator node) walker))
	   (else
	    (error "Illegal application type" node))))
	((snode? node)
	 (walker (snode-next node)))
	((pnode? node)
	 (eq-set-union (walker (pnode-consequent node))
		       (walker (pnode-alternative node))))
	(else
	 (error "Illegal node" node))))

(define *inlined-procedures*)

(define (walk-continuation continuation walker)
  (let ((rvalue (rvalue-known-value continuation)))
    (walker (and rvalue (continuation/entry-node rvalue)))))

(define (walk-node-for-variables node)
  (if node
      (if (parallel? node)
	  (walk-node-for-variables (order-parallel! node false))
	  (begin
	    (node-mark! node)
	    (or (node/bad-variables node)
		(let ((bad-variables
		       (eq-set-union
			(call-with-values (lambda () (find-node-values node))
			  values->variables)
			(walk-next node walk-node-for-variables))))
		  (set-node/bad-variables! node bad-variables)
		  bad-variables))))
      '()))

(define (find-node-values node)
  (let ((finish
	 (lambda (lvalue rvalue)
	   (values lvalue (if rvalue (list rvalue) '())))))
    (cfg-node-case (tagged-vector/tag node)
      ((APPLICATION)
       (case (application-type node)
	 ((COMBINATION)
	  (values false
		  (cons (combination/operator node)
			(combination/operands node))))
	 ((RETURN)
	  (finish false (return/operand node)))
	 (else
	  (error "Illegal application type" node))))
      ((VIRTUAL-RETURN)
       (finish false (virtual-return-operand node)))
      ((ASSIGNMENT)
       (finish (assignment-lvalue node)
	       (assignment-rvalue node)))
      ((DEFINITION)
       (finish (definition-lvalue node)
	       (definition-rvalue node)))
      ((STACK-OVERWRITE)
       (values (let ((target (stack-overwrite-target node)))
		 (and (lvalue? target) target))
	       '()))
      ((PARALLEL)
       (values false
	       (append-map subproblem-free-variables
			   (parallel-subproblems node))))
      ((POP FG-NOOP)
       (values false '()))
      ((TRUE-TEST)
       (finish false (true-test-rvalue node))))))

(define (values->variables lvalue rvalues)
  (eq-set-union
   (list->eq-set
    (and lvalue
	 (lvalue/variable? lvalue)
	 (interesting-variable? lvalue)
	 (list lvalue)))
   (map->eq-set (lambda (rvalue) (reference-lvalue rvalue))
		(filter (lambda (rvalue)
			  (and (rvalue/reference? rvalue)
			       (let ((lvalue (reference-lvalue rvalue)))
				 (and lvalue
				      (lvalue/variable? lvalue)
				      (interesting-variable? lvalue)))))
			rvalues))))

(define (complex-parallel-constraints subproblems vars-referenced-later)
  (call-with-values
      (lambda () (discriminate-items subproblems subproblem-simple?))
    (lambda (simple complex)
      (let ((discriminate-by-bad-vars
	     (lambda (subproblems)
	       (discriminate-items subproblems
		 (lambda (subproblem)
		   (any (lambda (var)
			  (memq var vars-referenced-later))
			(subproblem-free-variables subproblem))))))
	    (constraint-graph (make-constraint-graph)))
	(call-with-values (lambda () (discriminate-by-bad-vars simple))
	  (lambda (good-simples bad-simples)
	    (call-with-values (lambda () (discriminate-by-bad-vars complex))
	      (lambda (good-complex bad-complex)
		(add-constraint-set! good-simples
				     good-complex
				     constraint-graph)
		(add-constraint-set! good-complex
				     (append bad-simples bad-complex)
				     constraint-graph)))
	    constraint-graph))))))

(define-integrable (node/bad-variables node)
  (cfg-node-get node node/bad-variables-tag))

(define-integrable (set-node/bad-variables! node refs)
  (cfg-node-put! node node/bad-variables-tag refs))

(define node/bad-variables-tag
  "bad-variables-tag")

(define (bad-free-variables procedure)
  (append-map block-variables-nontransitively-free
	      (remove (lambda (block)
			(memq (block-procedure block) *inlined-procedures*))
		      (cdr (linearize-block-tree
			    (procedure-block procedure))))))

;;; Since the order of this linearization is not important we could
;;; make this routine more efficient. I'm not sure that it is worth
;;; it. If anyone does change it you should probably alter the line in
;;; bad-free-variables that says "(cdr (line..." to
;;; "(delq block (line..."
(define (linearize-block-tree block)
  (let ((children
	 (append (block-children block) (block-disowned-children block))))
    (if (null? children)
	(list block)
	(cons block (append-map! linearize-block-tree children)))))

(define (interesting-variable? variable)
  ;;; variables that will be in cells are eliminated from
  ;;; being put in registers because I couldn't figure out
  ;;; how to get the right code generated for them. Oh well,
  ;;; sigh!
  (not (or (variable-assigned? variable)
	   (variable-stack-overwrite-target? variable)
	   (variable/continuation-variable? variable)
	   (variable/value-variable? variable))))