#| -*-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.

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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.

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
;;; package: (compiler lap-syntaxer)

(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: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 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
  (ASSIGN (? target) (REGISTER (? comparand register-known-value)))
  (QUALIFIER (rtl:immediate-zero-constant? comparand))
  (list 'ASSIGN target (rtl:make-machine-constant 0)))

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

(define-rule rewriting
  (EQ-TEST (REGISTER (? comparand register-known-value)) (? source))
  (QUALIFIER (rtl:immediate-zero-constant? comparand))
  (list 'EQ-TEST source (rtl:make-machine-constant 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? (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

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

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

(define (rtl:simple-float-offset-address? expr)
  (and (rtl:float-offset-address? expr)
       (let ((offset (rtl:float-offset-address-offset expr)))
	 (or (rtl:machine-constant? offset)
	     (rtl:register? offset)
	     (and (rtl:object->datum? offset)
		  (rtl:register? (rtl:object->datum-expression offset)))))
       (let ((base (rtl:float-offset-address-base expr)))
	 (or (rtl:register? base)
	     (and (rtl:offset-address? base)
		  (let ((base* (rtl:offset-address-base base))
			(offset* (rtl:offset-address-offset base)))
		    (and (rtl:machine-constant? offset*)
			 (or (rtl:register? base*)
			     (and (rtl:object->address? base*)
				  (rtl:register?
				   (rtl:object->address-expression
				    base*)))))))))))