#| -*-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 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.

|#

;;;; RTL Rewrite Rules

(declare (usual-integrations))

;;;; Synthesized Data

(define-rule rewriting
  (CONS-NON-POINTER (REGISTER (? type register-known-value))
		    (REGISTER (? datum register-known-value)))
  (QUALIFIER (and (rtl:machine-constant? type)
		  (rtl:machine-constant? datum)))
  (rtl:make-cons-non-pointer type datum))

(define-rule rewriting
  (CONS-POINTER (REGISTER (? type register-known-value)) (? datum))
  (QUALIFIER
   (and (rtl:object->type? type)
	(rtl:constant? (rtl:object->type-expression type))))
  (rtl:make-cons-pointer
   (rtl:make-machine-constant
    (object-type (rtl:object->type-expression datum)))
   datum))

(define-rule rewriting
  (CONS-POINTER (REGISTER (? type register-known-value)) (? datum))
  (QUALIFIER (rtl:machine-constant? type))
  (rtl:make-cons-pointer type datum))

(define-rule rewriting
  (CONS-NON-POINTER (REGISTER (? type register-known-value)) (? datum))
  (QUALIFIER (rtl:machine-constant? type))
  (rtl:make-cons-non-pointer type datum))

(define-rule rewriting
  (CONS-NON-POINTER (REGISTER (? type register-known-value)) (? datum))
  (QUALIFIER
   (and (rtl:object->type? type)
	(rtl:constant? (rtl:object->type-expression type))))
  (rtl:make-cons-non-pointer
   (rtl:make-machine-constant
    (object-type (rtl:object->type-expression datum)))
   datum))

(define-rule rewriting
  (CONS-NON-POINTER (? type) (REGISTER (? datum register-known-value)))
  (QUALIFIER
   (and (rtl:object->datum? datum)
	(rtl:constant-non-pointer? (rtl:object->datum-expression datum))))
  (rtl:make-cons-non-pointer
   type
   (rtl:make-machine-constant
    (careful-object-datum
     (rtl:constant-value (rtl:object->datum-expression datum))))))

(define-rule rewriting
  (OBJECT->TYPE (REGISTER (? source register-known-value)))
  (QUALIFIER (rtl:constant? source))
  (rtl:make-machine-constant (object-type (rtl:constant-value source))))

(define-rule rewriting
  (OBJECT->DATUM (REGISTER (? source register-known-value)))
  (QUALIFIER (rtl:constant-non-pointer? source))
  (rtl:make-machine-constant
   (careful-object-datum (rtl:constant-value source))))

(define (rtl:constant-non-pointer? expression)
  (and (rtl:constant? expression)
       (non-pointer-object? (rtl:constant-value expression))))

;;; These rules are losers because there's no abstract way to cons a
;;; statement or a predicate without also getting some CFG structure.

(define-rule rewriting
  ;; Use register 0, always 0.
  (ASSIGN (? target) (REGISTER (? comparand register-known-value)))
  (QUALIFIER (rtl:immediate-zero-constant? comparand))
  (list 'ASSIGN target (rtl:make-machine-register 0)))

(define-rule rewriting
  ;; Compare to register 0, always 0.
  (EQ-TEST (? source) (REGISTER (? comparand register-known-value)))
  (QUALIFIER (rtl:immediate-zero-constant? comparand))
  (list 'EQ-TEST source (rtl:make-machine-register 0)))

(define-rule rewriting
  ;; Compare to register 0, always 0.
  (EQ-TEST (REGISTER (? comparand register-known-value)) (? source))
  (QUALIFIER (rtl:immediate-zero-constant? comparand))
  (list 'EQ-TEST source (rtl:make-machine-register 0)))

(define (rtl:immediate-zero-constant? expression)
  (cond ((rtl:constant? expression)
	 (let ((value (rtl:constant-value expression)))
	   (and (non-pointer-object? value)
		(zero? (object-type value))
		(zero? (careful-object-datum value)))))
	((rtl:cons-non-pointer? expression)
	 (and (let ((expression (rtl:cons-non-pointer-type expression)))
		(and (rtl:machine-constant? expression)
		     (zero? (rtl:machine-constant-value expression))))
	      (let ((expression (rtl:cons-non-pointer-datum expression)))
		(and (rtl:machine-constant? expression)
		     (zero? (rtl:machine-constant-value expression))))))
	(else false)))

;;;; Fixnums

;; I've copied this rule from the MC68020.  -- Jinx
;; It should probably be qualified to be in the immediate range.

(define-rule rewriting
  (OBJECT->FIXNUM (REGISTER (? source register-known-value)))
  (QUALIFIER (rtl:constant-fixnum? source))
  (rtl:make-object->fixnum source))

(define-rule rewriting
  (FIXNUM-2-ARGS FIXNUM-LSH
		 (? operand-1)
		 (REGISTER (? operand-2 register-known-value))
		 #F)
  (QUALIFIER (and (rtl:register? operand-1)
		  (rtl:constant-fixnum? operand-2)))
  (rtl:make-fixnum-2-args 'FIXNUM-LSH operand-1 operand-2 #F))

(define-rule rewriting
  (FIXNUM-2-ARGS MULTIPLY-FIXNUM
		 (REGISTER (? operand-1 register-known-value))
		 (? operand-2)
		 #F)
  (QUALIFIER (rtl:constant-fixnum-4? operand-1))
  (rtl:make-fixnum-2-args 'MULTIPLY-FIXNUM operand-1 operand-2 #F))

(define-rule rewriting
  (FIXNUM-2-ARGS MULTIPLY-FIXNUM
		 (? operand-1)
		 (REGISTER (? operand-2 register-known-value))
		 #F)
  (QUALIFIER (rtl:constant-fixnum-4? operand-2))
  (rtl:make-fixnum-2-args 'MULTIPLY-FIXNUM operand-1 operand-2 #F))

(define-rule rewriting
  (FIXNUM-2-ARGS MULTIPLY-FIXNUM
		 (REGISTER (? operand-1 register-known-value))
		 (? operand-2)
		 #F)
  (QUALIFIER
   (and (rtl:object->fixnum-of-register? operand-1)
	(rtl:constant-fixnum-4? operand-2)))
  (rtl:make-fixnum-2-args 'MULTIPLY-FIXNUM operand-1 operand-2 #F))

(define-rule rewriting
  (FIXNUM-2-ARGS MULTIPLY-FIXNUM
		 (? operand-1)
		 (REGISTER (? operand-2 register-known-value))
		 #F)
  (QUALIFIER
   (and (rtl:constant-fixnum-4? operand-1)
	(rtl:object->fixnum-of-register? operand-2)))
  (rtl:make-fixnum-2-args 'MULTIPLY-FIXNUM operand-1 operand-2 #F))

(define (rtl:constant-fixnum? expression)
  (and (rtl:constant? expression)
       (fix:fixnum? (rtl:constant-value expression))))

(define (rtl:constant-fixnum-4? expression)
  (and (rtl:object->fixnum? expression)
       (let ((expression (rtl:object->fixnum-expression expression)))
	 (and (rtl:constant? expression)
	      (eqv? 4 (rtl:constant-value expression))))))

(define (rtl:object->fixnum-of-register? expression)
   (and (rtl:object->fixnum? expression)
	(rtl:register? (rtl:object->fixnum-expression expression))))

;;;; Closures and other optimizations.  

(define-rule rewriting
  (CONS-POINTER (REGISTER (? type register-known-value))
		(REGISTER (? datum register-known-value)))
  (QUALIFIER (and (rtl:machine-constant? type)
		  (= (rtl:machine-constant-value type)
		     (ucode-type compiled-entry))
		  (or (rtl:entry:continuation? datum)
		      (rtl:entry:procedure? datum)
		      (rtl:cons-closure? datum))))
  (rtl:make-cons-pointer type datum))

(define-rule rewriting
  (FLOAT-OFFSET (REGISTER (? base register-known-value))
		(MACHINE-CONSTANT 0))
  (QUALIFIER (and (rtl:float-offset-address? base)
		  (rtl:simple-subexpressions? base)))
  (rtl:make-float-offset (rtl:float-offset-address-base base)
			 (rtl:float-offset-address-offset base)))

(define (rtl:simple-subexpressions? expr)
  (for-all? (cdr expr)
    (lambda (sub)
      (or (rtl:machine-constant? sub)
	  (rtl:register? sub)))))