src/compiler/policy.lisp

   1 ;;;; compiler optimization policy stuff
   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 ;;; a value for an optimization declaration
  15 (def!type policy-quality () '(integer 0 3))
  16
  17 ;;; global policy restrictions
  18 (defvar *policy-restrictions* nil)
  19
  20 (defun restrict-compiler-policy (&optional quality (min 0))
  21   #!+sb-doc
  22   "Assing a minimum value to an optimization quality. QUALITY is the name of
  23 the optimization quality to restrict, and MIN (defaulting to zero) is the
  24 minimum allowed value.
  25
  26 Returns the alist describing the current policy restrictions.
  27
  28 If QUALITY is NIL or not given, nothing is done.
  29
  30 Otherwise, if MIN is zero or not given, any existing restrictions of QUALITY
  31 are removed. If MIN is between one and three inclusive, it becomes the new
  32 minimum value for the optimization quality: any future proclamations or
  33 declarations of the quality with a value less then MIN behave as if the value
  34 was MIN instead.
  35
  36 This is intended to be used interactively, to facilitate recompiling large
  37 bodies of code with eg. a known minimum safety.
  38
  39 EXPERIMENTAL INTERFACE: Subject to change."
  40   (declare (type policy-quality min))
  41   (when quality
  42     (aver (policy-quality-name-p quality))
  43     (if (zerop min)
  44         (setf *policy-restrictions*
  45               (remove quality *policy-restrictions* :key #'car))
  46         (let ((cell (assoc quality *policy-restrictions*)))
  47           (if cell
  48               (setf (cdr cell) min)
  49               (push (cons quality min) *policy-restrictions*)))))
  50   *policy-restrictions*)
  51
  52 ;;; CMU CL used a special STRUCTURE-OBJECT type POLICY to represent
  53 ;;; the state of optimization policy at any point in compilation. This
  54 ;;; was a natural choice, but in SBCL it became a little troublesome
  55 ;;; because of stupid technicalities involving the cold initialization
  56 ;;; of structure LAYOUTs and structure accessors, so now we just use
  57 ;;; alists instead.
  58 (def!type policy () 'list)
  59
  60 (defstruct policy-dependent-quality
  61   name
  62   expression
  63   getter
  64   values-documentation)
  65
  66 ;;; names of recognized optimization policy qualities
  67 (defvar *policy-qualities*) ; (initialized at cold init)
  68 (defvar *policy-dependent-qualities* nil) ; alist of POLICY-DEPENDENT-QUALITYs
  69
  70 ;;; Is X the name of an optimization policy quality?
  71 (defun policy-quality-name-p (x)
  72   (or (memq x *policy-qualities*)
  73       (assq x *policy-dependent-qualities*)))
  74
  75 ;;; *POLICY* holds the current global compiler policy information, as
  76 ;;; an alist mapping from optimization quality name to quality value.
  77 ;;; Inside the scope of declarations, new entries are added at the
  78 ;;; head of the alist.
  79 (declaim (type policy *policy*))
  80 (defvar *policy*)          ; initialized in cold init
  81
  82 ;;; This is to be called early in cold init to set things up, and may
  83 ;;; also be called again later in cold init in order to reset default
  84 ;;; optimization policy back to default values after toplevel PROCLAIM
  85 ;;; OPTIMIZE forms have messed with it.
  86 (defun !policy-cold-init-or-resanify ()
  87   (setf *policy-qualities*
  88         '(;; ANSI standard qualities
  89           compilation-speed
  90           debug
  91           safety
  92           space
  93           speed
  94           ;; SBCL extensions
  95           ;;
  96           ;; FIXME: INHIBIT-WARNINGS is a misleading name for this.
  97           ;; Perhaps BREVITY would be better. But the ideal name would
  98           ;; have connotations of suppressing not warnings but only
  99           ;; optimization-related notes, which is already mostly the
 100           ;; behavior, and should probably become the exact behavior.
 101           ;; Perhaps INHIBIT-NOTES?
 102           inhibit-warnings))
 103   (setf *policy*
 104         (mapcar (lambda (name)
 105                   ;; CMU CL didn't use 1 as the default for
 106                   ;; everything, but since ANSI says 1 is the ordinary
 107                   ;; value, we do.
 108                   (cons name 1))
 109                 *policy-qualities*))
 110   (setf *policy-restrictions* nil)
 111   ;; not actually POLICY, but very similar
 112   (setf *handled-conditions* nil
 113         *disabled-package-locks* nil))
 114
 115 ;;; On the cross-compilation host, we initialize immediately (not
 116 ;;; waiting for "cold init", since cold init doesn't exist on
 117 ;;; cross-compilation host).
 118 #+sb-xc-host (!policy-cold-init-or-resanify)
 119
 120 ;;; Look up a named optimization quality in POLICY. This is only
 121 ;;; called by compiler code for known-valid QUALITY-NAMEs, e.g. SPEED;
 122 ;;; it's an error if it's called for a quality which isn't defined.
 123 (defun policy-quality (policy quality-name)
 124   (aver (policy-quality-name-p quality-name))
 125   (%policy-quality policy quality-name))
 126
 127 (defun %policy-quality (policy quality-name)
 128   (let* ((acons (assoc quality-name policy))
 129          (min (or (cdr (assoc quality-name *policy-restrictions*)) 0))
 130          (result (or (cdr acons) 1)))
 131     (max result min)))
 132
 133 ;;; syntactic sugar for querying optimization policy qualities
 134 ;;;
 135 ;;; Evaluate EXPR in terms of the optimization policy associated with
 136 ;;; THING. EXPR is a form which accesses optimization qualities by
 137 ;;; referring to them by name, e.g. (> SPEED SPACE).
 138 (defmacro policy (thing expr)
 139   (let* ((n-policy (gensym "N-POLICY-"))
 140          (binds (mapcar (lambda (name)
 141                           `(,name (policy-quality ,n-policy ',name)))
 142                         *policy-qualities*))
 143          (dependent-binds
 144           (loop for (name . info) in *policy-dependent-qualities*
 145                collect `(,name (let ((,name (policy-quality ,n-policy ',name)))
 146                                  (if (= ,name 1)
 147                                      ,(policy-dependent-quality-expression info)
 148                                      ,name))))))
 149     `(let* ((,n-policy (%coerce-to-policy ,thing)))
 150        (declare (ignorable ,n-policy))
 151        (symbol-macrolet (,@binds
 152                          ,@dependent-binds)
 153          ,expr))))
 154
 155 ;;; Dependent qualities
 156 (defmacro define-optimization-quality
 157     (name expression &optional values-documentation documentation)
 158   (declare (ignorable documentation))
 159   `(eval-when (:compile-toplevel :load-toplevel :execute)
 160      (let ((acons (assoc ',name *policy-dependent-qualities*))
 161            (item (make-policy-dependent-quality
 162                   :name ',name
 163                   :expression ',expression
 164                   :getter (lambda (policy) (policy policy ,expression))
 165                   :values-documentation ',values-documentation)))
 166        (if acons
 167            (setf (cdr acons) item)
 168            (setf *policy-dependent-qualities*
 169                  (nconc *policy-dependent-qualities* (list `(,',name . ,item))))))
 170      #-sb-xc-host
 171      ,@(when documentation `((setf (fdocumentation ',name 'optimize) ,documentation)))
 172      ',name))