#| -*-Scheme-*-

Copyright (C) 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994,
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    2017, 2018, 2019, 2020 Massachusetts Institute of Technology

This file is part of MIT/GNU Scheme.

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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
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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.

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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301,
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|#

;;;; RTL Generation: Combinations
;;; package: (compiler rtl-generator generate/combination)

(declare (usual-integrations))

(define (generate/combination combination)
  (if (combination/inline? combination)
      (combination/inline combination)
      (let ((model (combination/model combination)))
	((cond ((not model)
		(if (reference? (combination/operator combination))
		    invocation/reference
		    invocation/apply))
	       ((rvalue/constant? model)
		(if (primitive-procedure? (constant-value model))
		    invocation/primitive
		    invocation/apply))
	       ((rvalue/procedure? model)
		(case (procedure/type model)
		  ((OPEN-EXTERNAL OPEN-INTERNAL) invocation/jump)
		  ((CLOSURE TRIVIAL-CLOSURE)
		   ;; Known lexpr closures are invoked through apply.
		   ;; This makes the code simpler and probably does
		   ;; not matter much.
		   (if (procedure-rest model)
		       invocation/apply
		       invocation/jump))
		  ((IC) invocation/ic)
		  (else (error "Unknown procedure type" model))))
	       (else
		invocation/apply))
	 model
	 (combination/operator combination)
	 (combination/frame-size combination)
	 (let ((continuation (combination/continuation combination)))
	   (and (return-operator/subproblem? continuation)
		(not (continuation/always-known-operator? continuation))
		(continuation/label continuation)))
	 (prefix/append (generate/link-prefix combination)
			(generate/invocation-prefix combination))))))

;;;; Invocations

(define (invocation/jump model operator frame-size continuation prefix)
  (let ((callee (rvalue-known-value operator)))
    (scfg*scfg->scfg!
     (prefix frame-size 0)
     (cond ((not callee)
	    (if (not model)
		(error "invocation/jump: Going to hyperspace!"))
	    ((if (procedure-rest model)
		 rtl:make-invocation:computed-lexpr
		 rtl:make-invocation:computed-jump)
	     frame-size
	     continuation))
	   ((procedure-inline-code? callee)
	    (generate/procedure-entry/inline callee))
	   (else
	    (enqueue-procedure! callee)
	    (let ((trivial-call
		   (lambda ()
		     (rtl:make-invocation:jump
		      frame-size
		      continuation
		      (procedure-label callee)))))
	      (cond ((procedure-rest callee)
		     ;; Note that callee can't be a closure because of
		     ;; the dispatch in generate/combination!
		     (let* ((callee-block (procedure-block callee))
			    (core
			     (lambda (frame-size)
			       (rtl:make-invocation:lexpr
				(if (stack-block/static-link? callee-block)
				    (-1+ frame-size)
				    frame-size)
				continuation
				(procedure-label callee)))))
		       (if (not (block/dynamic-link? callee-block))
			   (core frame-size)
			   (scfg*scfg->scfg!
			    (rtl:make-push-link)
			    (core (1+ frame-size))))))
		    ((and (procedure/closure? callee)
			  (not (procedure/trivial-closure? callee)))
		     (let* ((block (procedure-closing-block callee))
			    (block* (block-shared-block block)))
		       (if (eq? block block*)
			   (trivial-call)
			   (invocation/adjust-closure-prefix block block*
							     (trivial-call)))))
		    (else
		     (trivial-call)))))))))

(define (invocation/adjust-closure-prefix block block* call-code)
  (let ((distance (closure-environment-adjustment
		   (block-number-of-entries block*)
		   (closure-block-entry-number block))))
    (if (zero? distance)
	call-code
	(let ((locative
	       (rtl:locative-offset
		(rtl:make-fetch (interpreter-stack-pointer))
		(stack->memory-offset 0))))
	  (scfg*scfg->scfg!
	   (rtl:make-assignment locative
				(rtl:bump-closure (rtl:make-fetch locative)
						  distance))
	   call-code)))))

(define (rtl:bump-closure closure distance)
  (rtl:make-typed-cons:procedure
   (rtl:make-address
    (rtl:locative-byte-offset closure distance))))

(define (invocation/apply model operator frame-size continuation prefix)
  model operator			; ignored
  (invocation/apply* frame-size 0 continuation prefix))

(define (invocation/apply* frame-size extra continuation prefix)
  (scfg*scfg->scfg! (prefix frame-size extra)
		    (rtl:make-invocation:apply frame-size continuation)))

(define invocation/ic
  ;; For now, use apply.  Later we can optimize for the cases where
  ;; the callee's closing frame is easily available, such as calling a
  ;; sibling, self-recursion, or an ancestor.
  invocation/apply)

(define (invocation/primitive model operator frame-size continuation prefix)
  model					; ignored
  (scfg*scfg->scfg!
   (prefix frame-size 0)
   (let ((primitive (constant-value (rvalue-known-value operator))))
     (if (not (primitive-arity-correct? primitive frame-size))
	 (error "Primitive called with incorrect number of arguments."
		primitive
		frame-size))
     ((or (special-primitive-handler primitive)
	  rtl:make-invocation:primitive)
      (1+ frame-size)
      continuation
      primitive))))

(package (invocation/reference)

(define-export (invocation/reference model operator frame-size continuation
				     prefix)
  model					; ignored
  (if (reference-to-known-location? operator)
      (invocation/apply* frame-size 0 continuation prefix)
      (let ((context (reference-context operator))
	    (variable (reference-lvalue operator)))
	(find-variable/value context variable
	  (lambda (expression)
	    (scfg*scfg->scfg!
	     (rtl:make-push expression)
	     (invocation/apply* (1+ frame-size) 1 continuation prefix)))
	  (lambda (environment name)
	    (invocation/lookup frame-size
			       continuation
			       (prefix frame-size 0)
			       environment
			       (intern-scode-variable!
				(reference-context/block context)
				name)))
	  (lambda (name)
	    (cond ((and (pair? name) (eq? (cdr name) '*GLOBAL*))
		   (invocation/global-link frame-size
					   continuation
					   (prefix frame-size 0)
					   (car name)))
		  ((memq 'UUO-LINK (variable-declarations variable))
		   (invocation/uuo-link frame-size
					continuation
					(prefix frame-size 0)
					name))
		  (else
		   (invocation/cache-reference frame-size
					       continuation
					       prefix
					       name))))))))

(define (invocation/lookup frame-size continuation prefix environment variable)
  (let ((make-invocation
	 (lambda (environment)
	   (expression-simplify-for-statement environment
	     (lambda (environment)
	       (rtl:make-invocation:lookup (1+ frame-size)
					   continuation
					   environment
					   variable))))))
    (if (cfg-null? prefix)
	(make-invocation environment)
	(scfg-append!
	 (rtl:make-assignment register:environment environment)
	 prefix
	 (make-invocation (rtl:make-fetch register:environment))))))

(define (invocation/uuo-link frame-size continuation prefix name)
  (scfg*scfg->scfg! prefix
		    (rtl:make-invocation:uuo-link (1+ frame-size)
						  continuation
						  name)))

(define (invocation/global-link frame-size continuation prefix name)
  (scfg*scfg->scfg! prefix
		    (rtl:make-invocation:global-link (1+ frame-size)
						     continuation
						     name)))

(define (invocation/cache-reference frame-size continuation prefix name)
  (load-temporary-register scfg*scfg->scfg!
			   (rtl:make-variable-cache name)
    (lambda (cell)
      (let ((contents (rtl:make-fetch cell)))
	(let ((n2
	       (rtl:make-type-test (rtl:make-object->type contents)
				   (ucode-type reference-trap)))
	      (n3
	       (scfg*scfg->scfg!
		(rtl:make-push contents)
		(invocation/apply* (1+ frame-size) 1 continuation prefix)))
	      (n4
	       (scfg*scfg->scfg!
		(prefix frame-size 0)
		(expression-simplify-for-statement cell
		  (lambda (cell)
		    (rtl:make-invocation:cache-reference (1+ frame-size)
							 continuation
							 cell))))))
	  (pcfg-consequent-connect! n2 n4)
	  (pcfg-alternative-connect! n2 n3)
	  (make-scfg (cfg-entry-node n2)
		     (hooks-union (scfg-next-hooks n3)
				  (scfg-next-hooks n4))))))))

;;; end INVOCATION/REFERENCE
)

;;;; Prefixes

(define (prefix/append prefix prefix*)
  (if prefix
      (if prefix*
	  (lambda (frame-size extra)
	    (scfg*scfg->scfg! (prefix frame-size extra)
			      (prefix* frame-size extra)))
	  prefix)
      (if prefix*
	  prefix*
	  (lambda (frame-size extra)
	    frame-size extra
	    (make-null-cfg)))))

(define (generate/link-prefix combination)
  (and (let ((callee (combination/model combination)))
	 (and callee
	      (rvalue/procedure? callee)
	      (block/dynamic-link? (procedure-block callee))))
       (if (return-operator/subproblem? (combination/continuation combination))
	   link-prefix/subproblem
	   (let ((context (combination/context combination)))
	     (let ((popping-limit
		    (block-popping-limit (reference-context/block context))))
	       (and popping-limit
		    (link-prefix/reduction context popping-limit)))))))

(define (link-prefix/subproblem frame-size extra)
  extra
  (rtl:make-assignment
   register:dynamic-link
   (rtl:make-address
    (stack-locative-offset (rtl:make-fetch register:stack-pointer)
			   frame-size))))

(define (link-prefix/reduction context block)
  (lambda (frame-size extra)
    frame-size
    (rtl:make-assignment register:dynamic-link
			 (popping-limit/locative context block extra 0))))

(define (generate/invocation-prefix combination)
  (let ((context (combination/context combination))
	(overwritten-block (combination/reuse-existing-frame? combination)))
    (if overwritten-block
	(invocation-prefix/reuse-adjustment context overwritten-block)
	(let ((adjustment (combination/frame-adjustment combination)))
	  (and adjustment
	       (let ((block (cdr adjustment)))
		 (cond ((eq? (car adjustment) 'KNOWN)
			(invocation-prefix/move-frame-up context block))
		       ((block/external? block)
			;; If the adjustment is external, it says to
			;; try and pop all of the stack frames for
			;; this procedure.  We need not compare the
			;; dynamic link to the adjustment pointer
			;; because the dynamic link will always be
			;; less than or equal to the adjustment
			;; pointer.
			(lambda (frame-size extra)
			  (make-move-frame-up
			   frame-size
			   (stack-locative-offset (interpreter-dynamic-link)
						  extra))))
		       (else
			(invocation-prefix/dynamic-link context block)))))))))

(define (invocation-prefix/reuse-adjustment context block)
  (lambda (frame-size extra)
    ;; We've overwritten `(- frame-size extra)' items starting at `block',
    ;; and pushed another `extra' items at the top of stack.  We must
    ;; shift the `extra' items down to be adjacent to the overwritten
    ;; items.  Usually, `extra' is zero, in which case this just means
    ;; adjusting the stack pointer to the appropriate place.
    (let ((overwriting-size (- frame-size extra)))
      (if (<= (let loop ((block* (reference-context/block context)))
		(let ((size (block-frame-size block*)))
		   (if (eq? block block*)
		       size
		       (+ size (loop (block-parent block*))))))
	      overwriting-size)
	  ;; We've overwritten everything; no shift required.
	  (make-null-cfg)
	  (let ((locative
		 (popping-limit/locative context
					 block
					 extra
					 (- overwriting-size))))
	    (if (zero? extra)
		(rtl:make-assignment register:stack-pointer locative)
		(make-move-frame-up extra locative)))))))

(define (invocation-prefix/move-frame-up context block)
  (lambda (frame-size extra)
    (make-move-frame-up frame-size
			(popping-limit/locative context block extra 0))))

(define (make-move-frame-up frame-size locative)
  (expression-simplify-for-statement
   locative
   (lambda (locative)
     (rtl:make-invocation-prefix:move-frame-up frame-size locative))))

(define (invocation-prefix/dynamic-link context block)
  (lambda (frame-size extra)
    (expression-simplify-for-statement
     (popping-limit/locative context block extra 0)
     (lambda (locative)
       (expression-simplify-for-statement (interpreter-dynamic-link)
	 (lambda (dynamic-link)
	   (rtl:make-invocation-prefix:dynamic-link frame-size
						    locative
						    dynamic-link)))))))