src/compiler/constantp.lisp

   1 ;;;; implementation of CONSTANTP, needs both INFO and IR1-ATTRIBUTES
   2
   3 ;;;; This software is part of the SBCL system. See the README file for
   4 ;;;; more information.
   5 ;;;;
   6 ;;;; This software is derived from the CMU CL system, which was
   7 ;;;; written at Carnegie Mellon University and released into the
   8 ;;;; public domain. The software is in the public domain and is
   9 ;;;; provided with absolutely no warranty. See the COPYING and CREDITS
  10 ;;;; files for more information.
  11
  12 (in-package "SB!C")
  13
  14 (!begin-collecting-cold-init-forms)
  15
  16 (defvar *special-form-constantp-funs*)
  17 (declaim (type hash-table *special-form-constantp-funs*))
  18 (!cold-init-forms
  19   (setf *special-form-constantp-funs* (make-hash-table)))
  20
  21 (defvar *special-form-constant-form-value-funs*)
  22 (declaim (type hash-table *special-form-constant-form-value-funs*))
  23 (!cold-init-forms
  24   (setf *special-form-constant-form-value-funs* (make-hash-table)))
  25
  26 (defvar *special-constant-variables*)
  27 (!cold-init-forms
  28   (setf *special-constant-variables* nil))
  29
  30 (defun %constantp (form environment envp)
  31   (let ((form (if envp
  32                   (sb!xc:macroexpand form environment)
  33                   form)))
  34     (typecase form
  35       ;; This INFO test catches KEYWORDs as well as explicitly
  36       ;; DEFCONSTANT symbols.
  37       (symbol
  38        (or (eq (info :variable :kind form) :constant)
  39            (constant-special-variable-p form)))
  40       (list
  41        (or (constant-special-form-p form environment envp)
  42            #-sb-xc-host
  43            (values (constant-function-call-p form environment envp))))
  44       (t t))))
  45
  46 (defun %constant-form-value (form environment envp)
  47   (let ((form (if envp
  48                   (sb!xc:macroexpand form environment)
  49                   form)))
  50     (typecase form
  51       (symbol
  52        (symbol-value form))
  53       (list
  54        (if (special-operator-p (car form))
  55            (constant-special-form-value form environment envp)
  56            #-sb-xc-host
  57            (constant-function-call-value form environment envp)))
  58       (t
  59        form))))
  60
  61 (defun constant-special-form-p (form environment envp)
  62   (let ((fun (gethash (car form) *special-form-constantp-funs*)))
  63     (when fun
  64       (funcall fun form environment envp))))
  65
  66 (defun constant-special-form-value (form environment envp)
  67   (let ((fun (gethash (car form) *special-form-constant-form-value-funs*)))
  68     (if fun
  69         (funcall fun form environment envp)
  70         (error "Not a constant-foldable special form: ~S" form))))
  71
  72 (defun constant-special-variable-p (name)
  73   (and (member name *special-constant-variables*) t))
  74
  75 ;;; FIXME: It would be nice to deal with inline functions
  76 ;;; too.
  77 (defun constant-function-call-p (form environment envp)
  78   (let ((name (car form)))
  79     (if (and (legal-fun-name-p name)
  80              (eq :function (info :function :kind name))
  81              (let ((info (info :function :info name)))
  82                (and info (ir1-attributep (fun-info-attributes info)
  83                                          foldable)))
  84              (and (every (lambda (arg)
  85                            (%constantp arg environment envp))
  86                          (cdr form))))
  87         ;; Even though the function may be marked as foldable
  88         ;; the call may still signal an error -- eg: (CAR 1).
  89         (handler-case
  90             (values t (constant-function-call-value form environment envp))
  91           (error ()
  92             (values nil nil)))
  93         (values nil nil))))
  94
  95 (defun constant-function-call-value (form environment envp)
  96   (apply (fdefinition (car form))
  97          (mapcar (lambda (arg)
  98                    (%constant-form-value arg environment envp))
  99                  (cdr form))))
 100
 101 #!-sb-fluid (declaim (inline sb!xc:constantp))
 102 (defun sb!xc:constantp (form &optional (environment nil envp))
 103   #!+sb-doc
 104   "True of any FORM that has a constant value: self-evaluating objects,
 105 keywords, defined constants, quote forms. Additionally the
 106 constant-foldability of some function calls special forms is recognized. If
 107 ENVIRONMENT is provided the FORM is first macroexpanded in it."
 108   (%constantp form environment envp))
 109
 110 #!-sb-fluid (declaim (inline constant-form-value))
 111 (defun constant-form-value (form &optional (environment nil envp))
 112   #!+sb-doc
 113   "Returns the value of the constant FORM in ENVIRONMENT. Behaviour
 114 is undefined unless CONSTANTP has been first used to determine the
 115 constantness of the FORM in ENVIRONMENT."
 116   (%constant-form-value form environment envp))
 117
 118 (declaim (inline constant-typep))
 119 (defun constant-typep (form type &optional (environment nil envp))
 120   (and (%constantp form environment envp)
 121        ;; FIXME: We probably should be passing the environment to
 122        ;; TYPEP too, but (1) our XC version of typep AVERs that the
 123        ;; environment is null (2) our real version ignores it anyhow.
 124        (sb!xc:typep (%constant-form-value form environment envp) type)))
 125
 126 ;;;; NOTE!!!
 127 ;;;;
 128 ;;;; If you add new special forms, check that they do not
 129 ;;;; alter the logic of existing ones: eg, currently
 130 ;;;; CONSTANT-FORM-VALUE directly evaluates the last expression
 131 ;;;; of a PROGN, as no assignment is allowed. If you extend
 132 ;;;; analysis to assignments then other forms must take this
 133 ;;;; into account.
 134
 135 (defmacro defconstantp (operator lambda-list &key test eval)
 136   (with-unique-names (form environment envp)
 137     (flet ((frob (body)
 138              `(flet ((constantp* (x)
 139                        (%constantp x ,environment ,envp))
 140                      (constant-form-value* (x)
 141                        (%constant-form-value x ,environment ,envp)))
 142                 (declare (ignorable #'constantp* #'constant-form-value*))
 143                 (destructuring-bind ,lambda-list (cdr ,form)
 144                   ;; KLUDGE: is all we need, so we keep it simple
 145                   ;; instead of general (not handling cases like &key (x y))
 146                   (declare (ignorable
 147                             ,@(remove-if (lambda (arg)
 148                                            (member arg sb!xc:lambda-list-keywords))
 149                                          lambda-list)))
 150                    ,body))))
 151       `(progn
 152          (setf (gethash ',operator *special-form-constantp-funs*)
 153                (lambda (,form ,environment ,envp)
 154                  ,(frob test)))
 155          (setf (gethash ',operator *special-form-constant-form-value-funs*)
 156                (lambda (,form ,environment ,envp)
 157                  ,(frob eval)))))))
 158
 159 (!cold-init-forms
 160  (defconstantp quote (value)
 161    :test t
 162    :eval value)
 163
 164  (defconstantp if (test then &optional else)
 165    :test
 166    (and (constantp* test)
 167         (constantp* (if (constant-form-value* test)
 168                         then
 169                         else)))
 170    :eval (if (constant-form-value* test)
 171              (constant-form-value* then)
 172              (constant-form-value* else)))
 173
 174  (defconstantp progn (&body forms)
 175    :test (every #'constantp* forms)
 176    :eval (constant-form-value* (car (last forms))))
 177
 178  (defconstantp unwind-protect (protected-form &body cleanup-forms)
 179    :test (every #'constantp* (cons protected-form cleanup-forms))
 180    :eval (constant-form-value* protected-form))
 181
 182  (defconstantp the (type form)
 183    :test (and (constantp* form)
 184               (handler-case
 185                   ;; in case the type-spec is malformed!
 186                   (typep (constant-form-value* form) type)
 187                 (error () nil)))
 188    :eval (constant-form-value* form))
 189
 190  (defconstantp block (name &body forms)
 191    ;; We currently fail to detect cases like
 192    ;;
 193    ;; (BLOCK FOO
 194    ;;   ...CONSTANT-FORMS...
 195    ;;   (RETURN-FROM FOO CONSTANT-VALUE)
 196    ;;   ...ANYTHING...)
 197    ;;
 198    ;; Right now RETURN-FROM kills the constantness unequivocally.
 199    :test (every #'constantp* forms)
 200    :eval (constant-form-value* (car (last forms))))
 201
 202  (defconstantp multiple-value-prog1 (first-form &body forms)
 203    :test (every #'constantp* (cons first-form forms))
 204    :eval (constant-form-value* first-form))
 205
 206  (defconstantp progv (symbols values &body forms)
 207    :test (and (constantp* symbols)
 208               (constantp* values)
 209               (let* ((symbol-values (constant-form-value* symbols))
 210                      (*special-constant-variables*
 211                       (append symbol-values *special-constant-variables*)))
 212                 (progv
 213                     symbol-values
 214                     (constant-form-value* values)
 215                   (every #'constantp* forms))))
 216    :eval (progv
 217              (constant-form-value* symbols)
 218              (constant-form-value* values)
 219            (constant-form-value* (car (last forms))))))
 220
 221 (!defun-from-collected-cold-init-forms !constantp-cold-init)
 222