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[sbcl.git] / src / compiler / ltn.lisp

;;;; This file contains the LTN pass in the compiler. LTN allocates
;;;; expression evaluation TNs, makes nearly all the implementation
;;;; policy decisions, and also does a few other miscellaneous things.

;;;; This software is part of the SBCL system. See the README file for
;;;; more information.
;;;;
;;;; This software is derived from the CMU CL system, which was
;;;; written at Carnegie Mellon University and released into the
;;;; public domain. The software is in the public domain and is
;;;; provided with absolutely no warranty. See the COPYING and CREDITS
;;;; files for more information.

(in-package "SB!C")
\f
;;;; utilities

;;; Return the LTN-POLICY indicated by the node policy.
;;;
;;; FIXME: It would be tidier to use an LTN-POLICY object (an instance
;;; of DEFSTRUCT LTN-POLICY) instead of a keyword, and have queries
;;; like LTN-POLICY-SAFE-P become slot accessors. If we do this,
;;; grep for and carefully review use of literal keywords, so that
;;; things like
;;;   (EQ (TEMPLATE-LTN-POLICY TEMPLATE) :SAFE)
;;; don't get overlooked.
;;;
;;; FIXME: Classic CMU CL went to some trouble to cache LTN-POLICY
;;; values in LTN-ANALYZE so that they didn't have to be recomputed on
;;; every block. I stripped that out (the whole DEFMACRO FROB thing)
;;; because I found it too confusing. Thus, it might be that the 
;;; new uncached code spends an unreasonable amount of time in
;;; this lookup function. This function should be profiled, and if
;;; it's a significant contributor to runtime, we can cache it in
;;; some more local way, e.g. by adding a CACHED-LTN-POLICY slot to
;;; the NODE structure, and doing something like
;;;   (DEFUN NODE-LTN-POLICY (NODE)
;;;     (OR (NODE-CACHED-LTN-POLICY NODE)
;;;         (SETF (NODE-CACHED-LTN-POLICY NODE)
;;;               (NODE-UNCACHED-LTN-POLICY NODE)))
(defun node-ltn-policy (node)
  (declare (type node node))
  (policy node
          (let ((eff-space (max space
                                ;; on the theory that if the code is
                                ;; smaller, it will take less time to
                                ;; compile (could lose if the smallest
                                ;; case is out of line, and must
                                ;; allocate many linkage registers):
                                compilation-speed)))
            (if (zerop safety)
                (if (>= speed eff-space) :fast :small)
                (if (>= speed eff-space) :fast-safe :safe)))))

;;; Return true if LTN-POLICY is a safe policy.
(defun ltn-policy-safe-p (ltn-policy)
  (ecase ltn-policy
    ((:safe :fast-safe) t)
    ((:small :fast) nil)))

;;; Called when an unsafe policy indicates that no type check should
;;; be done on CONT. We delete the type check unless it is :ERROR
;;; (indicating a compile-time type error.)
(defun flush-type-check (cont)
  (declare (type continuation cont))
  (when (member (continuation-type-check cont) '(t :no-check))
    (setf (continuation-%type-check cont) :deleted))
  (values))

;;; an annotated continuation's primitive-type
#!-sb-fluid (declaim (inline continuation-ptype))
(defun continuation-ptype (cont)
  (declare (type continuation cont))
  (ir2-continuation-primitive-type (continuation-info cont)))

;;; Return true if a constant LEAF is of a type which we can legally
;;; directly reference in code. Named constants with arbitrary pointer
;;; values cannot, since we must preserve EQLness.
(defun legal-immediate-constant-p (leaf)
  (declare (type constant leaf))
  (or (not (leaf-has-source-name-p leaf))
      (typecase (constant-value leaf)
        ((or number character) t)
        (symbol (symbol-package (constant-value leaf)))
        (t nil))))

;;; If CONT is used only by a REF to a leaf that can be delayed, then
;;; return the leaf, otherwise return NIL.
(defun continuation-delayed-leaf (cont)
  (declare (type continuation cont))
  (let ((use (continuation-use cont)))
    (and (ref-p use)
         (let ((leaf (ref-leaf use)))
           (etypecase leaf
             (lambda-var (if (null (lambda-var-sets leaf)) leaf nil))
             (constant (if (legal-immediate-constant-p leaf) leaf nil))
             ((or functional global-var) nil))))))

;;; Annotate a normal single-value continuation. If its only use is a
;;; ref that we are allowed to delay the evaluation of, then we mark
;;; the continuation for delayed evaluation, otherwise we assign a TN
;;; to hold the continuation's value. If the continuation has a type
;;; check, we make the TN according to the proven type to ensure that
;;; the possibly erroneous value can be represented.
(defun annotate-1-value-continuation (cont)
  (declare (type continuation cont))
  (let ((info (continuation-info cont)))
    (aver (eq (ir2-continuation-kind info) :fixed))
    (cond
     ((continuation-delayed-leaf cont)
      (setf (ir2-continuation-kind info) :delayed))
     ((member (continuation-type-check cont) '(:deleted nil))
      (setf (ir2-continuation-locs info)
            (list (make-normal-tn (ir2-continuation-primitive-type info)))))
     (t
      (setf (ir2-continuation-locs info)
            (list (make-normal-tn
                   (primitive-type
                    (single-value-type (continuation-proven-type cont)))))))))
  (values))

;;; Make an IR2-CONTINUATION corresponding to the continuation type
;;; and then do ANNOTATE-1-VALUE-CONTINUATION. If POLICY-KEYWORD isn't
;;; a safe policy keyword, then we clear the TYPE-CHECK flag.
(defun annotate-ordinary-continuation (cont ltn-policy)
  (declare (type continuation cont)
           (type ltn-policy ltn-policy))
  (let ((info (make-ir2-continuation
               (primitive-type (continuation-type cont)))))
    (setf (continuation-info cont) info)
    (unless (ltn-policy-safe-p ltn-policy)
      (flush-type-check cont))
    (annotate-1-value-continuation cont))
  (values))

;;; Annotate the function continuation for a full call. If the only
;;; reference is to a global function and DELAY is true, then we delay
;;; the reference, otherwise we annotate for a single value.
;;;
;;; Unlike for an argument, we only clear the type check flag when the
;;; LTN-POLICY is unsafe, since the check for a valid function
;;; object must be done before the call.
(defun annotate-fun-continuation (cont ltn-policy &optional (delay t))
  (declare (type continuation cont) (type ltn-policy ltn-policy))
  (unless (ltn-policy-safe-p ltn-policy)
    (flush-type-check cont))
  (let* ((ptype (primitive-type (continuation-type cont)))
         (tn-ptype (if (member (continuation-type-check cont) '(:deleted nil))
                       ptype
                       (primitive-type
                        (single-value-type
                         (continuation-proven-type cont)))))
         (info (make-ir2-continuation ptype)))
    (setf (continuation-info cont) info)
    (let ((name (continuation-fun-name cont t)))
      (if (and delay name)
          (setf (ir2-continuation-kind info) :delayed)
          (setf (ir2-continuation-locs info)
                (list (make-normal-tn tn-ptype))))))
  (values))

;;; If TAIL-P is true, then we check to see whether the call can really
;;; be a tail call by seeing if this function's return convention is :UNKNOWN.
;;; If so, we move the call block succssor link from the return block to
;;; the component tail (after ensuring that they are in separate blocks.)
;;; This allows the return to be deleted when there are no non-tail uses.
(defun flush-full-call-tail-transfer (call)
  (declare (type basic-combination call))
  (let ((tails (and (node-tail-p call)
                    (lambda-tail-set (node-home-lambda call)))))
    (when tails
      (cond ((eq (return-info-kind (tail-set-info tails)) :unknown)
             (node-ends-block call)
             (let ((block (node-block call)))
               (unlink-blocks block (first (block-succ block)))
               (link-blocks block (component-tail (block-component block)))))
            (t
             (setf (node-tail-p call) nil)))))
  (values))

;;; We set the kind to :FULL or :FUNNY, depending on whether there is an
;;; IR2-CONVERT method. If a funny function, then we inhibit tail recursion
;;; and type check normally, since the IR2 convert method is going to want to
;;; deliver values normally. We still annotate the function continuation,
;;; since IR2tran might decide to call after all.
;;;
;;; If not funny, we always flush arg type checks, but do it after
;;; annotation when the LTN-POLICY is safe, since we don't want to
;;; choose the TNs according to a type assertions that may not hold.
;;;
;;; Note that args may already be annotated because template selection can
;;; bail out to here.
(defun ltn-default-call (call ltn-policy)
  (declare (type combination call) (type ltn-policy ltn-policy))
  (let ((kind (basic-combination-kind call)))
    (annotate-fun-continuation (basic-combination-fun call) ltn-policy)

    (cond
     ((and (fun-info-p kind)
           (fun-info-ir2-convert kind))
      (setf (basic-combination-info call) :funny)
      (setf (node-tail-p call) nil)
      (dolist (arg (basic-combination-args call))
        (unless (continuation-info arg)
          (setf (continuation-info arg)
                (make-ir2-continuation
                 (primitive-type
                  (continuation-type arg)))))
        (annotate-1-value-continuation arg)))
     (t
      (let ((safe-p (ltn-policy-safe-p ltn-policy)))
        (dolist (arg (basic-combination-args call))
          (unless safe-p (flush-type-check arg))
          (unless (continuation-info arg)
            (setf (continuation-info arg)
                  (make-ir2-continuation
                   (primitive-type
                    (continuation-type arg)))))
          (annotate-1-value-continuation arg)
          (when safe-p (flush-type-check arg))))
      (when (eq kind :error)
        (setf (basic-combination-kind call) :full))
      (setf (basic-combination-info call) :full)
      (flush-full-call-tail-transfer call))))

  (values))

;;; Annotate a continuation for unknown multiple values:
;;; -- Delete any type check, regardless of LTN-POLICY, since IR2
;;;    conversion isn't prepared to check unknown-values continuations.
;;;    If we delete a type check when the policy is safe, then we emit
;;;    a warning.
;;; -- Add the continuation to the IR2-BLOCK-POPPED if it is used
;;;    across a block boundary.
;;; -- Assign an :UNKNOWN IR2-CONTINUATION.
;;;
;;; Note: it is critical that this be called only during LTN analysis
;;; of CONT's DEST, and called in the order that the continuations are
;;; received. Otherwise the IR2-BLOCK-POPPED and
;;; IR2-COMPONENT-VALUES-FOO would get all messed up.
(defun annotate-unknown-values-continuation (cont ltn-policy)
  (declare (type continuation cont) (type ltn-policy ltn-policy))
  (when (eq (continuation-type-check cont) t)
    (let* ((dest (continuation-dest cont))
           (*compiler-error-context* dest))
      (when (and (ltn-policy-safe-p ltn-policy)
                 (policy dest (>= safety inhibit-warnings)))
        (compiler-note "compiler limitation: ~
                        unable to check type assertion in ~
                        unknown-values context:~%  ~S"
                       (continuation-asserted-type cont))))
    (setf (continuation-%type-check cont) :deleted))

  (let* ((block (node-block (continuation-dest cont)))
         (use (continuation-use cont))
         (2block (block-info block)))
    (unless (and use (eq (node-block use) block))
      (setf (ir2-block-popped 2block)
            (nconc (ir2-block-popped 2block) (list cont)))))

  (let ((2cont (make-ir2-continuation nil)))
    (setf (ir2-continuation-kind 2cont) :unknown)
    (setf (ir2-continuation-locs 2cont) (make-unknown-values-locations))
    (setf (continuation-info cont) 2cont))

  (values))

;;; Annotate CONT for a fixed, but arbitrary number of values, of the
;;; specified primitive TYPES. If the continuation has a type check,
;;; we annotate for the number of values indicated by TYPES, but only
;;; use proven type information.
(defun annotate-fixed-values-continuation (cont ltn-policy types)
  (declare (continuation cont) (ltn-policy ltn-policy) (list types))
  (unless (ltn-policy-safe-p ltn-policy)
    (flush-type-check cont))
  (let ((res (make-ir2-continuation nil)))
    (if (member (continuation-type-check cont) '(:deleted nil))
        (setf (ir2-continuation-locs res) (mapcar #'make-normal-tn types))
        (let* ((proven (mapcar (lambda (x)
                                 (make-normal-tn (primitive-type x)))
                               (values-types
                                (continuation-proven-type cont))))
               (num-proven (length proven))
               (num-types (length types)))
          (setf (ir2-continuation-locs res)
                (cond
                 ((< num-proven num-types)
                  (append proven
                          (make-n-tns (- num-types num-proven)
                                      *backend-t-primitive-type*)))
                 ((> num-proven num-types)
                  (subseq proven 0 num-types))
                 (t
                  proven)))))
    (setf (continuation-info cont) res))
  (values))
\f
;;;; node-specific analysis functions

;;; Annotate the result continuation for a function. We use the
;;; RETURN-INFO computed by GTN to determine how to represent the
;;; return values within the function:
;;;  * If the TAIL-SET has a fixed values count, then use that
;;;    many values.
;;;  * If the actual uses of the result continuation in this function
;;;    have a fixed number of values (after intersection with the
;;;    assertion), then use that number. We throw out TAIL-P :FULL
;;;    and :LOCAL calls, since we know they will truly end up as TR
;;;    calls. We can use the BASIC-COMBINATION-INFO even though it
;;;    is assigned by this phase, since the initial value NIL doesn't
;;;    look like a TR call.
;;;      If there are *no* non-tail-call uses, then it falls out
;;;    that we annotate for one value (type is NIL), but the return
;;;    will end up being deleted.
;;;      In non-perverse code, the DFO walk will reach all uses of
;;;    the result continuation before it reaches the RETURN. In
;;;    perverse code, we may annotate for unknown values when we
;;;    didn't have to.
;;; * Otherwise, we must annotate the continuation for unknown values.
(defun ltn-analyze-return (node ltn-policy)
  (declare (type creturn node) (type ltn-policy ltn-policy))
  (let* ((cont (return-result node))
         (fun (return-lambda node))
         (returns (tail-set-info (lambda-tail-set fun)))
         (types (return-info-types returns)))
    (if (eq (return-info-count returns) :unknown)
        (collect ((res *empty-type* values-type-union))
          (do-uses (use (return-result node))
            (unless (and (node-tail-p use)
                         (basic-combination-p use)
                         (member (basic-combination-info use) '(:local :full)))
              (res (node-derived-type use))))

          (let ((int (values-type-intersection
                      (res)
                      (continuation-asserted-type cont))))
            (multiple-value-bind (types kind)
                (values-types (if (eq int *empty-type*) (res) int))
              (if (eq kind :unknown)
                  (annotate-unknown-values-continuation cont ltn-policy)
                  (annotate-fixed-values-continuation
                   cont ltn-policy (mapcar #'primitive-type types))))))
        (annotate-fixed-values-continuation cont ltn-policy types)))

  (values))

;;; Annotate the single argument continuation as a fixed-values
;;; continuation. We look at the called lambda to determine number and
;;; type of return values desired. It is assumed that only a function
;;; that LOOKS-LIKE-AN-MV-BIND will be converted to a local call.
(defun ltn-analyze-mv-bind (call ltn-policy)
  (declare (type mv-combination call)
           (type ltn-policy ltn-policy))
  (setf (basic-combination-kind call) :local)
  (setf (node-tail-p call) nil)
  (annotate-fixed-values-continuation
   (first (basic-combination-args call))
   ltn-policy
   (mapcar (lambda (var)
             (primitive-type (basic-var-type var)))
           (lambda-vars
            (ref-leaf
             (continuation-use
              (basic-combination-fun call))))))
  (values))

;;; We force all the argument continuations to use the unknown values
;;; convention. The continuations are annotated in reverse order,
;;; since the last argument is on top, thus must be popped first. We
;;; disallow delayed evaluation of the function continuation to
;;; simplify IR2 conversion of MV call.
;;;
;;; We could be cleverer when we know the number of values returned by
;;; the continuations, but optimizations of MV call are probably
;;; unworthwhile.
;;;
;;; We are also responsible for handling THROW, which is represented
;;; in IR1 as an MV call to the %THROW funny function. We annotate the
;;; tag continuation for a single value and the values continuation
;;; for unknown values.
(defun ltn-analyze-mv-call (call ltn-policy)
  (declare (type mv-combination call) (type ltn-policy ltn-policy))
  (let ((fun (basic-combination-fun call))
        (args (basic-combination-args call)))
    (cond ((eq (continuation-fun-name fun) '%throw)
           (setf (basic-combination-info call) :funny)
           (annotate-ordinary-continuation (first args) ltn-policy)
           (annotate-unknown-values-continuation (second args) ltn-policy)
           (setf (node-tail-p call) nil))
          (t
           (setf (basic-combination-info call) :full)
           (annotate-fun-continuation (basic-combination-fun call)
                                      ltn-policy
                                      nil)
           (dolist (arg (reverse args))
             (annotate-unknown-values-continuation arg ltn-policy))
           (flush-full-call-tail-transfer call))))

  (values))

;;; Annotate the arguments as ordinary single-value continuations. And
;;; check the successor.
(defun ltn-analyze-local-call (call ltn-policy)
  (declare (type combination call)
           (type ltn-policy ltn-policy))
  (setf (basic-combination-info call) :local)
  (dolist (arg (basic-combination-args call))
    (when arg
      (annotate-ordinary-continuation arg ltn-policy)))
  (when (node-tail-p call)
    (set-tail-local-call-successor call))
  (values))

;;; Make sure that a tail local call is linked directly to the bind
;;; node. Usually it will be, but calls from XEPs and calls that might have
;;; needed a cleanup after them won't have been swung over yet, since we
;;; weren't sure they would really be TR until now. Also called by byte
;;; compiler.
(defun set-tail-local-call-successor (call)
  (let ((caller (node-home-lambda call))
        (callee (combination-lambda call)))
    (aver (eq (lambda-tail-set caller)
              (lambda-tail-set (lambda-home callee))))
    (node-ends-block call)
    (let ((block (node-block call)))
      (unlink-blocks block (first (block-succ block)))
      (link-blocks block (lambda-block callee))))
  (values))

;;; Annotate the value continuation.
(defun ltn-analyze-set (node ltn-policy)
  (declare (type cset node) (type ltn-policy ltn-policy))
  (setf (node-tail-p node) nil)
  (annotate-ordinary-continuation (set-value node) ltn-policy)
  (values))

;;; If the only use of the TEST continuation is a combination
;;; annotated with a conditional template, then don't annotate the
;;; continuation so that IR2 conversion knows not to emit any code,
;;; otherwise annotate as an ordinary continuation. Since we only use
;;; a conditional template if the call immediately precedes the IF
;;; node in the same block, we know that any predicate will already be
;;; annotated.
(defun ltn-analyze-if (node ltn-policy)
  (declare (type cif node) (type ltn-policy ltn-policy))
  (setf (node-tail-p node) nil)
  (let* ((test (if-test node))
         (use (continuation-use test)))
    (unless (and (combination-p use)
                 (let ((info (basic-combination-info use)))
                   (and (template-p info)
                        (eq (template-result-types info) :conditional))))
      (annotate-ordinary-continuation test ltn-policy)))
  (values))

;;; If there is a value continuation, then annotate it for unknown
;;; values. In this case, the exit is non-local, since all other exits
;;; are deleted or degenerate by this point.
(defun ltn-analyze-exit (node ltn-policy)
  (setf (node-tail-p node) nil)
  (let ((value (exit-value node)))
    (when value
      (annotate-unknown-values-continuation value ltn-policy)))
  (values))

;;; We need a special method for %UNWIND-PROTECT that ignores the
;;; cleanup function. We don't annotate either arg, since we don't
;;; need them at run-time.
;;;
;;; (The default is o.k. for %CATCH, since environment analysis
;;; converted the reference to the escape function into a constant
;;; reference to the NLX-INFO.)
(defoptimizer (%unwind-protect ltn-annotate) ((escape cleanup)
                                              node
                                              ltn-policy)
  ltn-policy ; a hack to effectively (DECLARE (IGNORE LTN-POLICY))
  (setf (basic-combination-info node) :funny)
  (setf (node-tail-p node) nil))
\f
;;;; known call annotation

;;; Return true if RESTR is satisfied by TYPE. If T-OK is true, then a
;;; T restriction allows any operand type. This is also called by IR2
;;; translation when it determines whether a result temporary needs to
;;; be made, and by representation selection when it is deciding which
;;; move VOP to use. CONT and TN are used to test for constant
;;; arguments.
(defun operand-restriction-ok (restr type &key cont tn (t-ok t))
  (declare (type (or (member *) cons) restr)
           (type primitive-type type)
           (type (or continuation null) cont)
           (type (or tn null) tn))
  (if (eq restr '*)
      t
      (ecase (first restr)
        (:or
         (dolist (mem (rest restr) nil)
           (when (or (and t-ok (eq mem *backend-t-primitive-type*))
                     (eq mem type))
             (return t))))
        (:constant
         (cond (cont
                (and (constant-continuation-p cont)
                     (funcall (second restr) (continuation-value cont))))
               (tn
                (and (eq (tn-kind tn) :constant)
                     (funcall (second restr) (tn-value tn))))
               (t
                (error "Neither CONT nor TN supplied.")))))))

;;; Check that the argument type restriction for TEMPLATE are
;;; satisfied in call. If an argument's TYPE-CHECK is :NO-CHECK and
;;; our policy is safe, then only :SAFE templates are OK.
(defun template-args-ok (template call safe-p)
  (declare (type template template)
           (type combination call))
  (let ((mtype (template-more-args-type template)))
    (do ((args (basic-combination-args call) (cdr args))
         (types (template-arg-types template) (cdr types)))
        ((null types)
         (cond ((null args) t)
               ((not mtype) nil)
               (t
                (dolist (arg args t)
                  (unless (operand-restriction-ok mtype
                                                  (continuation-ptype arg))
                    (return nil))))))
      (when (null args) (return nil))
      (let ((arg (car args))
            (type (car types)))
        (when (and (eq (continuation-type-check arg) :no-check)
                   safe-p
                   (not (eq (template-ltn-policy template) :safe)))
          (return nil))
        (unless (operand-restriction-ok type (continuation-ptype arg)
                                        :cont arg)
          (return nil))))))

;;; Check that TEMPLATE can be used with the specifed RESULT-TYPE.
;;; Result type checking is pretty different from argument type
;;; checking due to the relaxed rules for values count. We succeed if
;;; for each required result, there is a positional restriction on the
;;; value that is at least as good. If we run out of result types
;;; before we run out of restrictions, then we only succeed if the
;;; leftover restrictions are *. If we run out of restrictions before
;;; we run out of result types, then we always win.
(defun template-results-ok (template result-type)
  (declare (type template template)
           (type ctype result-type))
  (when (template-more-results-type template)
    (error "~S has :MORE results with :TRANSLATE." (template-name template)))
  (let ((types (template-result-types template)))
    (cond
     ((values-type-p result-type)
      (do ((ltypes (append (args-type-required result-type)
                           (args-type-optional result-type))
                   (rest ltypes))
           (types types (rest types)))
          ((null ltypes)
           (dolist (type types t)
             (unless (eq type '*)
               (return nil))))
        (when (null types) (return t))
        (let ((type (first types)))
          (unless (operand-restriction-ok type
                                          (primitive-type (first ltypes)))
            (return nil)))))
     (types
      (operand-restriction-ok (first types) (primitive-type result-type)))
     (t t))))

;;; Return true if CALL is an ok use of TEMPLATE according to SAFE-P.
;;; -- If the template has a GUARD that isn't true, then we ignore the
;;;    template, not even considering it to be rejected.
;;; -- If the argument type restrictions aren't satisfied, then we
;;;    reject the template.
;;; -- If the template is :CONDITIONAL, then we accept it only when the
;;;    destination of the value is an immediately following IF node.
;;; -- If either the template is safe or the policy is unsafe (i.e. we
;;;    can believe output assertions), then we test against the
;;;    intersection of the node derived type and the continuation
;;;    asserted type. Otherwise, we just use the node type. If
;;;    TYPE-CHECK is null, there is no point in doing the intersection,
;;;    since the node type must be a subtype of the  assertion.
;;;
;;; If the template is *not* ok, then the second value is a keyword
;;; indicating which aspect failed.
(defun is-ok-template-use (template call safe-p)
  (declare (type template template) (type combination call))
  (let* ((guard (template-guard template))
         (cont (node-cont call))
         (atype (continuation-asserted-type cont))
         (dtype (node-derived-type call)))
    (cond ((and guard (not (funcall guard)))
           (values nil :guard))
          ((not (template-args-ok template call safe-p))
           (values nil
                   (if (and safe-p (template-args-ok template call nil))
                       :arg-check
                       :arg-types)))
          ((eq (template-result-types template) :conditional)
           (let ((dest (continuation-dest cont)))
             (if (and (if-p dest)
                      (immediately-used-p (if-test dest) call))
                 (values t nil)
                 (values nil :conditional))))
          ((template-results-ok
            template
            (if (and (or (eq (template-ltn-policy template) :safe)
                         (not safe-p))
                     (continuation-type-check cont))
                (values-type-intersection dtype atype)
                dtype))
           (values t nil))
          (t
           (values nil :result-types)))))

;;; Use operand type information to choose a template from the list
;;; TEMPLATES for a known CALL. We return three values:
;;; 1. The template we found.
;;; 2. Some template that we rejected due to unsatisfied type restrictions, or
;;;    NIL if none.
;;; 3. The tail of Templates for templates we haven't examined yet.
;;;
;;; We just call IS-OK-TEMPLATE-USE until it returns true.
(defun find-template (templates call safe-p)
  (declare (list templates) (type combination call))
  (do ((templates templates (rest templates))
       (rejected nil))
      ((null templates)
       (values nil rejected nil))
    (let ((template (first templates)))
      (when (is-ok-template-use template call safe-p)
        (return (values template rejected (rest templates))))
      (setq rejected template))))

;;; Given a partially annotated known call and a translation policy,
;;; return the appropriate template, or NIL if none can be found. We
;;; scan the templates (ordered by increasing cost) looking for a
;;; template whose restrictions are satisfied and that has our policy.
;;;
;;; If we find a template that doesn't have our policy, but has a
;;; legal alternate policy, then we also record that to return as a
;;; last resort. If our policy is safe, then only safe policies are
;;; O.K., otherwise anything goes.
;;;
;;; If we find a template with :SAFE policy, then we return it, or any
;;; cheaper fallback template. The theory behind this is that if it is
;;; cheapest, small and safe, we can't lose. If it is not cheapest,
;;; then we use the fallback, which won't have the desired policy, but
;;; :SAFE isn't desired either, so we might as well go with the
;;; cheaper one. The main reason for doing this is to make sure that
;;; cheap safe templates are used when they apply and the current
;;; policy is something else. This is useful because :SAFE has the
;;; additional semantics of implicit argument type checking, so we may
;;; be forced to define a template with :SAFE policy when it is really
;;; small and fast as well.
(defun find-template-for-ltn-policy (call ltn-policy)
  (declare (type combination call)
           (type ltn-policy ltn-policy))
  (let ((safe-p (ltn-policy-safe-p ltn-policy))
        (current (fun-info-templates (basic-combination-kind call)))
        (fallback nil)
        (rejected nil))
    (loop
     (multiple-value-bind (template this-reject more)
         (find-template current call safe-p)
       (unless rejected
         (setq rejected this-reject))
       (setq current more)
       (unless template
         (return (values fallback rejected)))
       (let ((tcpolicy (template-ltn-policy template)))
         (cond ((eq tcpolicy ltn-policy)
                (return (values template rejected)))
               ((eq tcpolicy :safe)
                (return (values (or fallback template) rejected)))
               ((or (not safe-p) (eq tcpolicy :fast-safe))
                (unless fallback
                  (setq fallback template)))))))))

(defvar *efficiency-note-limit* 2
  #!+sb-doc
  "This is the maximum number of possible optimization alternatives will be
  mentioned in a particular efficiency note. NIL means no limit.")
(declaim (type (or index null) *efficiency-note-limit*))

(defvar *efficiency-note-cost-threshold* 5
  #!+sb-doc
  "This is the minumum cost difference between the chosen implementation and
  the next alternative that justifies an efficiency note.")
(declaim (type index *efficiency-note-cost-threshold*))

;;; This function is called by NOTE-REJECTED-TEMPLATES when it can't
;;; figure out any reason why TEMPLATE was rejected. Users should
;;; never see these messages, but they can happen in situations where
;;; the VM definition is messed up somehow.
(defun strange-template-failure (template call ltn-policy frob)
  (declare (type template template) (type combination call)
           (type ltn-policy ltn-policy) (type function frob))
  (funcall frob "This shouldn't happen!  Bug?")
  (multiple-value-bind (win why)
      (is-ok-template-use template call (ltn-policy-safe-p ltn-policy))
    (aver (not win))
    (ecase why
      (:guard
       (funcall frob "template guard failed"))
      (:arg-check
       (funcall frob "The template isn't safe, yet we were counting on it."))
      (:arg-types
       (funcall frob "argument types invalid")
       (funcall frob "argument primitive types:~%  ~S"
                (mapcar (lambda (x)
                          (primitive-type-name
                           (continuation-ptype x)))
                        (combination-args call)))
       (funcall frob "argument type assertions:~%  ~S"
                (mapcar (lambda (x)
                          (if (atom x)
                              x
                              (ecase (car x)
                                (:or `(:or .,(mapcar #'primitive-type-name
                                                     (cdr x))))
                                (:constant `(:constant ,(third x))))))
                        (template-arg-types template))))
      (:conditional
       (funcall frob "conditional in a non-conditional context"))
      (:result-types
       (funcall frob "result types invalid")))))

;;; This function emits efficiency notes describing all of the
;;; templates better (faster) than TEMPLATE that we might have been
;;; able to use if there were better type declarations. Template is
;;; null when we didn't find any template, and thus must do a full
;;; call.
;;;
;;; In order to be worth complaining about, a template must:
;;; -- be allowed by its guard,
;;; -- be safe if the current policy is safe,
;;; -- have argument/result type restrictions consistent with the
;;;    known type information, e.g. we don't consider float templates
;;;    when an operand is known to be an integer,
;;; -- be disallowed by the stricter operand subtype test (which
;;;    resembles, but is not identical to the test done by
;;;    FIND-TEMPLATE.)
;;;
;;; Note that there may not be any possibly applicable templates,
;;; since we are called whenever any template is rejected. That
;;; template might have the wrong policy or be inconsistent with the
;;; known type.
;;;
;;; We go to some trouble to make the whole multi-line output into a
;;; single call to COMPILER-NOTE so that repeat messages are
;;; suppressed, etc.
(defun note-rejected-templates (call ltn-policy template)
  (declare (type combination call) (type ltn-policy ltn-policy)
           (type (or template null) template))

  (collect ((losers))
    (let ((safe-p (ltn-policy-safe-p ltn-policy))
          (verbose-p (policy call (= inhibit-warnings 0)))
          (max-cost (- (template-cost
                        (or template
                            (template-or-lose 'call-named)))
                       *efficiency-note-cost-threshold*)))
      (dolist (try (fun-info-templates (basic-combination-kind call)))
        (when (> (template-cost try) max-cost) (return)) ; FIXME: UNLESS'd be cleaner.
        (let ((guard (template-guard try)))
          (when (and (or (not guard) (funcall guard))
                     (or (not safe-p)
                         (ltn-policy-safe-p (template-ltn-policy try)))
                     (or verbose-p
                         (and (template-note try)
                              (valid-fun-use
                               call (template-type try)
                               :argument-test #'types-equal-or-intersect
                               :result-test
                               #'values-types-equal-or-intersect))))
            (losers try)))))

    (when (losers)
      (collect ((messages)
                (count 0 +))
        (flet ((lose1 (string &rest stuff)
                 (messages string)
                 (messages stuff)))
          (dolist (loser (losers))
            (when (and *efficiency-note-limit*
                       (>= (count) *efficiency-note-limit*))
              (lose1 "etc.")
              (return))
            (let* ((type (template-type loser))
                   (valid (valid-fun-use call type))
                   (strict-valid (valid-fun-use call type
                                                :strict-result t)))
              (lose1 "unable to do ~A (cost ~W) because:"
                     (or (template-note loser) (template-name loser))
                     (template-cost loser))
              (cond
               ((and valid strict-valid)
                (strange-template-failure loser call ltn-policy #'lose1))
               ((not valid)
                (aver (not (valid-fun-use call type
                                          :lossage-fun #'lose1
                                          :unwinnage-fun #'lose1))))
               (t
                (aver (ltn-policy-safe-p ltn-policy))
                (lose1 "can't trust output type assertion under safe policy")))
              (count 1))))

        (let ((*compiler-error-context* call))
          (compiler-note "~{~?~^~&~6T~}"
                         (if template
                             `("forced to do ~A (cost ~W)"
                               (,(or (template-note template)
                                     (template-name template))
                                ,(template-cost template))
                               . ,(messages))
                             `("forced to do full call"
                               nil
                               . ,(messages))))))))
  (values))

;;; Flush type checks according to policy. If the policy is
;;; unsafe, then we never do any checks. If our policy is safe, and
;;; we are using a safe template, then we can also flush arg and
;;; result type checks. Result type checks are only flushed when the
;;; continuation as a single use. Result type checks are not flush if
;;; the policy is safe because the selection of template for results
;;; readers assumes the type check is done (uses the derived type
;;; which is the intersection of the proven and asserted types).
(defun flush-type-checks-according-to-ltn-policy (call ltn-policy template)
  (declare (type combination call) (type ltn-policy ltn-policy)
           (type template template))
  (let ((safe-op (eq (template-ltn-policy template) :safe)))
    (when (or (not (ltn-policy-safe-p ltn-policy)) safe-op)
      (dolist (arg (basic-combination-args call))
        (flush-type-check arg)))
    (when safe-op
      (let ((cont (node-cont call)))
        (when (and (eq (continuation-use cont) call)
                   (not (ltn-policy-safe-p ltn-policy)))
          (flush-type-check cont)))))

  (values))

;;; If a function has a special-case annotation method use that,
;;; otherwise annotate the argument continuations and try to find a
;;; template corresponding to the type signature. If there is none,
;;; convert a full call.
(defun ltn-analyze-known-call (call ltn-policy)
  (declare (type combination call)
           (type ltn-policy ltn-policy))
  (let ((method (fun-info-ltn-annotate (basic-combination-kind call)))
        (args (basic-combination-args call)))
    (when method
      (funcall method call ltn-policy)
      (return-from ltn-analyze-known-call (values)))

    (dolist (arg args)
      (setf (continuation-info arg)
            (make-ir2-continuation (primitive-type (continuation-type arg)))))

    (multiple-value-bind (template rejected)
        (find-template-for-ltn-policy call ltn-policy)
      ;; If we are unable to use some templates due to unsatisfied
      ;; operand type restrictions and our policy enables efficiency
      ;; notes, then we call NOTE-REJECTED-TEMPLATES.
      (when (and rejected
                 (policy call (> speed inhibit-warnings)))
        (note-rejected-templates call ltn-policy template))
      ;; If we are forced to do a full call, we check to see whether
      ;; the function called is the same as the current function. If
      ;; so, we give a warning, as this is probably a botched attempt
      ;; to implement an out-of-line version in terms of inline
      ;; transforms or VOPs or whatever.
      (unless template
        (when (let ((funleaf (physenv-lambda (node-physenv call))))
                (and (leaf-has-source-name-p funleaf)
                     (eq (continuation-fun-name (combination-fun call))
                         (leaf-source-name funleaf))
                     (let ((info (basic-combination-kind call)))
                       (not (or (fun-info-ir2-convert info)
                                (ir1-attributep (fun-info-attributes info)
                                                recursive))))))
          (let ((*compiler-error-context* call))
            (compiler-warn "~@<recursion in known function definition~2I ~
                            ~_policy=~S ~_arg types=~S~:>"
                           (lexenv-policy (node-lexenv call))
                           (mapcar (lambda (arg)
                                     (type-specifier (continuation-type arg)))
                                   args))))
        (ltn-default-call call ltn-policy)
        (return-from ltn-analyze-known-call (values)))
      (setf (basic-combination-info call) template)
      (setf (node-tail-p call) nil)

      (flush-type-checks-according-to-ltn-policy call ltn-policy template)

      (dolist (arg args)
        (annotate-1-value-continuation arg))))

  (values))
\f
;;;; interfaces

;;; most of the guts of the two interface functions: Compute the
;;; policy and dispatch to the appropriate node-specific function.
;;;
;;; Note: we deliberately don't use the DO-NODES macro, since the
;;; block can be split out from underneath us, and DO-NODES would scan
;;; past the block end in that case.
(defun ltn-analyze-block (block)
  (do* ((node (continuation-next (block-start block))
              (continuation-next cont))
        (cont (node-cont node) (node-cont node))
        (ltn-policy (node-ltn-policy node) (node-ltn-policy node)))
      (nil)
    (etypecase node
      (ref)
      (combination
       (case (basic-combination-kind node)
         (:local (ltn-analyze-local-call node ltn-policy))
         ((:full :error) (ltn-default-call node ltn-policy))
         (t
          (ltn-analyze-known-call node ltn-policy))))
      (cif
       (ltn-analyze-if node ltn-policy))
      (creturn
       (ltn-analyze-return node ltn-policy))
      ((or bind entry))
      (exit
       (ltn-analyze-exit node ltn-policy))
      (cset (ltn-analyze-set node ltn-policy))
      (mv-combination
       (ecase (basic-combination-kind node)
         (:local
          (ltn-analyze-mv-bind node ltn-policy))
         ((:full :error)
          (ltn-analyze-mv-call node ltn-policy)))))
    (when (eq node (block-last block))
      (return))))

;;; Loop over the blocks in COMPONENT, doing stuff to nodes that
;;; receive values. In addition to the stuff done by FROB, we also see
;;; whether there are any unknown values receivers, making notations
;;; in the components' GENERATORS and RECEIVERS as appropriate.
;;;
;;; If any unknown-values continations are received by this block (as
;;; indicated by IR2-BLOCK-POPPED), then we add the block to the
;;; IR2-COMPONENT-VALUES-RECEIVERS.
;;;
;;; This is where we allocate IR2 blocks because it is the first place
;;; we need them.
(defun ltn-analyze (component)
  (declare (type component component))
  (let ((2comp (component-info component)))
    (do-blocks (block component)
      ;; This assertion seems to protect us from compiling a component
      ;; twice. As noted above, "this is where we allocate IR2-BLOCKS
      ;; because it is the first place we need them", so if one is
      ;; already allocated here, something is wrong. -- WHN 2001-09-14
      (aver (not (block-info block)))
      (let ((2block (make-ir2-block block)))
        (setf (block-info block) 2block)
        (ltn-analyze-block block)
        (let ((popped (ir2-block-popped 2block)))
          (when popped
            (push block (ir2-component-values-receivers 2comp)))))))
  (values))

;;; This function is used to analyze blocks that must be added to the
;;; flow graph after the normal LTN phase runs. Such code is
;;; constrained not to use weird unknown values (and probably in lots
;;; of other ways).
(defun ltn-analyze-belated-block (block)
  (declare (type cblock block))
  (ltn-analyze-block block)
  (aver (not (ir2-block-popped (block-info block))))
  (values))