0.6.11.23:

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

;;;; This file implements local call analysis. A local call is a
;;;; function call between functions being compiled at the same time.
;;;; If we can tell at compile time that such a call is legal, then we
;;;; change the combination to call the correct lambda, mark it as
;;;; local, and add this link to our call graph. Once a call is local,
;;;; it is then eligible for let conversion, which places the body of
;;;; the function inline.
;;;;
;;;; We cannot always do a local call even when we do have the
;;;; function being called. Calls that cannot be shown to have legal
;;;; arg counts are not converted.

;;;; 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")

;;; This function propagates information from the variables in the function
;;; Fun to the actual arguments in Call. This is also called by the VALUES IR1
;;; optimizer when it sleazily converts MV-BINDs to LETs.
;;;
;;; We flush all arguments to Call that correspond to unreferenced variables
;;; in Fun. We leave NILs in the Combination-Args so that the remaining args
;;; still match up with their vars.
;;;
;;; We also apply the declared variable type assertion to the argument
;;; continuations.
(defun propagate-to-args (call fun)
  (declare (type combination call) (type clambda fun))
  (do ((args (basic-combination-args call) (cdr args))
       (vars (lambda-vars fun) (cdr vars)))
      ((null args))
    (let ((arg (car args))
          (var (car vars)))
      (cond ((leaf-refs var)
             (assert-continuation-type arg (leaf-type var)))
            (t
             (flush-dest arg)
             (setf (car args) nil)))))

  (values))

;;; This function handles merging the tail sets if Call is potentially
;;; tail-recursive, and is a call to a function with a different TAIL-SET than
;;; Call's Fun. This must be called whenever we alter IR1 so as to place a
;;; local call in what might be a TR context. Note that any call which returns
;;; its value to a RETURN is considered potentially TR, since any implicit
;;; MV-PROG1 might be optimized away.
;;;
;;; We destructively modify the set for the calling function to represent both,
;;; and then change all the functions in callee's set to reference the first.
;;; If we do merge, we reoptimize the RETURN-RESULT continuation to cause
;;; IR1-OPTIMIZE-RETURN to recompute the tail set type.
(defun merge-tail-sets (call &optional (new-fun (combination-lambda call)))
  (declare (type basic-combination call) (type clambda new-fun))
  (let ((return (continuation-dest (node-cont call))))
    (when (return-p return)
      (let ((call-set (lambda-tail-set (node-home-lambda call)))
            (fun-set (lambda-tail-set new-fun)))
        (unless (eq call-set fun-set)
          (let ((funs (tail-set-functions fun-set)))
            (dolist (fun funs)
              (setf (lambda-tail-set fun) call-set))
            (setf (tail-set-functions call-set)
                  (nconc (tail-set-functions call-set) funs)))
          (reoptimize-continuation (return-result return))
          t)))))

;;; Convert a combination into a local call. We PROPAGATE-TO-ARGS, set
;;; the combination kind to :LOCAL, add FUN to the CALLS of the
;;; function that the call is in, call MERGE-TAIL-SETS, then replace
;;; the function in the REF node with the new function.
;;;
;;; We change the REF last, since changing the reference can trigger
;;; LET conversion of the new function, but will only do so if the
;;; call is local. Note that the replacement may trigger LET
;;; conversion or other changes in IR1. We must call MERGE-TAIL-SETS
;;; with NEW-FUN before the substitution, since after the substitution
;;; (and LET conversion), the call may no longer be recognizable as
;;; tail-recursive.
(defun convert-call (ref call fun)
  (declare (type ref ref) (type combination call) (type clambda fun))
  (propagate-to-args call fun)
  (setf (basic-combination-kind call) :local)
  (pushnew fun (lambda-calls (node-home-lambda call)))
  (merge-tail-sets call fun)
  (change-ref-leaf ref fun)
  (values))
\f
;;;; external entry point creation

;;; Return a Lambda form that can be used as the definition of the XEP
;;; for FUN.
;;;
;;; If FUN is a lambda, then we check the number of arguments
;;; (conditional on policy) and call FUN with all the arguments.
;;;
;;; If FUN is an OPTIONAL-DISPATCH, then we dispatch off of the number
;;; of supplied arguments by doing do an = test for each entry-point,
;;; calling the entry with the appropriate prefix of the passed
;;; arguments.
;;;
;;; If there is a more arg, then there are a couple of optimizations
;;; that we make (more for space than anything else):
;;; -- If MIN-ARGS is 0, then we make the more entry a T clause, since 
;;;    no argument count error is possible.
;;; -- We can omit the = clause for the last entry-point, allowing the 
;;;    case of 0 more args to fall through to the more entry.
;;;
;;; We don't bother to policy conditionalize wrong arg errors in
;;; optional dispatches, since the additional overhead is negligible
;;; compared to the cost of everything else going on.
;;;
;;; Note that if policy indicates it, argument type declarations in
;;; Fun will be verified. Since nothing is known about the type of the
;;; XEP arg vars, type checks will be emitted when the XEP's arg vars
;;; are passed to the actual function.
(defun make-xep-lambda (fun)
  (declare (type functional fun))
  (etypecase fun
    (clambda
     (let ((nargs (length (lambda-vars fun)))
           (n-supplied (gensym))
           (temps (make-gensym-list (length (lambda-vars fun)))))
       `(lambda (,n-supplied ,@temps)
          (declare (type index ,n-supplied))
          ,(if (policy nil (zerop safety))
               `(declare (ignore ,n-supplied))
               `(%verify-argument-count ,n-supplied ,nargs))
          (%funcall ,fun ,@temps))))
    (optional-dispatch
     (let* ((min (optional-dispatch-min-args fun))
            (max (optional-dispatch-max-args fun))
            (more (optional-dispatch-more-entry fun))
            (n-supplied (gensym))
            (temps (make-gensym-list max)))
       (collect ((entries))
         (do ((eps (optional-dispatch-entry-points fun) (rest eps))
              (n min (1+ n)))
             ((null eps))
           (entries `((= ,n-supplied ,n)
                      (%funcall ,(first eps) ,@(subseq temps 0 n)))))
         `(lambda (,n-supplied ,@temps)
            ;; FIXME: Make sure that INDEX type distinguishes between
            ;; target and host. (Probably just make the SB!XC:DEFTYPE
            ;; different from CL:DEFTYPE.)
            (declare (type index ,n-supplied))
            (cond
             ,@(if more (butlast (entries)) (entries))
             ,@(when more
                 `((,(if (zerop min) 't `(>= ,n-supplied ,max))
                    ,(let ((n-context (gensym))
                           (n-count (gensym)))
                       `(multiple-value-bind (,n-context ,n-count)
                            (%more-arg-context ,n-supplied ,max)
                          (%funcall ,more ,@temps ,n-context ,n-count))))))
             (t
              (%argument-count-error ,n-supplied)))))))))

;;; Make an external entry point (XEP) for FUN and return it. We
;;; convert the result of MAKE-XEP-LAMBDA in the correct environment,
;;; then associate this lambda with FUN as its XEP. After the
;;; conversion, we iterate over the function's associated lambdas,
;;; redoing local call analysis so that the XEP calls will get
;;; converted. We also bind *LEXENV* to change the compilation policy
;;; over to the interface policy.
;;;
;;; We set REANALYZE and REOPTIMIZE in the component, just in case we
;;; discover an XEP after the initial local call analyze pass.
(defun make-external-entry-point (fun)
  (declare (type functional fun))
  (aver (not (functional-entry-function fun)))
  (with-ir1-environment (lambda-bind (main-entry fun))
    (let* ((*lexenv* (make-lexenv :policy (make-interface-policy *lexenv*)))
           (res (ir1-convert-lambda (make-xep-lambda fun))))
      (setf (functional-kind res) :external)
      (setf (leaf-ever-used res) t)
      (setf (functional-entry-function res) fun)
      (setf (functional-entry-function fun) res)
      (setf (component-reanalyze *current-component*) t)
      (setf (component-reoptimize *current-component*) t)
      (etypecase fun
        (clambda (local-call-analyze-1 fun))
        (optional-dispatch
         (dolist (ep (optional-dispatch-entry-points fun))
           (local-call-analyze-1 ep))
         (when (optional-dispatch-more-entry fun)
           (local-call-analyze-1 (optional-dispatch-more-entry fun)))))
      res)))

;;; Notice a Ref that is not in a local-call context. If the Ref is
;;; already to an XEP, then do nothing, otherwise change it to the
;;; XEP, making an XEP if necessary.
;;;
;;; If Ref is to a special :Cleanup or :Escape function, then we treat
;;; it as though it was not an XEP reference (i.e. leave it alone.)
(defun reference-entry-point (ref)
  (declare (type ref ref))
  (let ((fun (ref-leaf ref)))
    (unless (or (external-entry-point-p fun)
                (member (functional-kind fun) '(:escape :cleanup)))
      (change-ref-leaf ref (or (functional-entry-function fun)
                               (make-external-entry-point fun))))))
\f
;;; Attempt to convert all references to Fun to local calls. The
;;; reference must be the function for a call, and the function
;;; continuation must be used only once, since otherwise we cannot be
;;; sure what function is to be called. The call continuation would be
;;; multiply used if there is hairy stuff such as conditionals in the
;;; expression that computes the function.
;;;
;;; If we cannot convert a reference, then we mark the referenced
;;; function as an entry-point, creating a new XEP if necessary. We
;;; don't try to convert calls that are in error (:ERROR kind.)
;;;
;;; This is broken off from Local-Call-Analyze so that people can
;;; force analysis of newly introduced calls. Note that we don't do
;;; LET conversion here.
(defun local-call-analyze-1 (fun)
  (declare (type functional fun))
  (let ((refs (leaf-refs fun))
        (first-time t))
    (dolist (ref refs)
      (let* ((cont (node-cont ref))
             (dest (continuation-dest cont)))
        (cond ((and (basic-combination-p dest)
                    (eq (basic-combination-fun dest) cont)
                    (eq (continuation-use cont) ref))

               (convert-call-if-possible ref dest)

               (unless (eq (basic-combination-kind dest) :local)
                 (reference-entry-point ref)))
              (t
               (reference-entry-point ref))))
      (setq first-time nil)))

  (values))

;;; We examine all New-Functions in component, attempting to convert
;;; calls into local calls when it is legal. We also attempt to
;;; convert each lambda to a LET. LET conversion is also triggered by
;;; deletion of a function reference, but functions that start out
;;; eligible for conversion must be noticed sometime.
;;;
;;; Note that there is a lot of action going on behind the scenes
;;; here, triggered by reference deletion. In particular, the
;;; COMPONENT-LAMBDAS are being hacked to remove newly deleted and let
;;; converted lambdas, so it is important that the lambda is added to
;;; the COMPONENT-LAMBDAS when it is. Also, the
;;; COMPONENT-NEW-FUNCTIONS may contain all sorts of drivel, since it
;;; is not updated when we delete functions, etc. Only
;;; COMPONENT-LAMBDAS is updated.
;;;
;;; COMPONENT-REANALYZE-FUNCTIONS is treated similarly to
;;; NEW-FUNCTIONS, but we don't add lambdas to the LAMBDAS.
(defun local-call-analyze (component)
  (declare (type component component))
  (loop
    (let* ((new (pop (component-new-functions component)))
           (fun (or new (pop (component-reanalyze-functions component)))))
      (unless fun (return))
      (let ((kind (functional-kind fun)))
        (cond ((member kind '(:deleted :let :mv-let :assignment)))
              ((and (null (leaf-refs fun)) (eq kind nil)
                    (not (functional-entry-function fun)))
               (delete-functional fun))
              (t
               (when (and new (lambda-p fun))
                 (push fun (component-lambdas component)))
               (local-call-analyze-1 fun)
               (when (lambda-p fun)
                 (maybe-let-convert fun)))))))

  (values))

;;; If policy is auspicious, CALL is not in an XEP, and we don't seem
;;; to be in an infinite recursive loop, then change the reference to
;;; reference a fresh copy. We return whichever function we decide to
;;; reference.
(defun maybe-expand-local-inline (fun ref call)
  (if (and (policy call
                   (and (>= speed space) (>= speed compilation-speed)))
           (not (eq (functional-kind (node-home-lambda call)) :external))
           (not *converting-for-interpreter*)
           (inline-expansion-ok call))
      (with-ir1-environment call
        (let* ((*lexenv* (functional-lexenv fun))
               (won nil)
               (res (catch 'local-call-lossage
                      (prog1
                          (ir1-convert-lambda (functional-inline-expansion fun))
                        (setq won t)))))
          (cond (won
                 (change-ref-leaf ref res)
                 res)
                (t
                 (let ((*compiler-error-context* call))
                   (compiler-note "couldn't inline expand because expansion ~
                                   calls this let-converted local function:~
                                   ~%  ~S"
                                  (leaf-name res)))
                 fun))))
      fun))

;;; Dispatch to the appropriate function to attempt to convert a call. Ref
;;; most be a reference to a FUNCTIONAL. This is called in IR1 optimize as
;;; well as in local call analysis. If the call is is already :Local, we do
;;; nothing. If the call is already scheduled for deletion, also do nothing
;;; (in addition to saving time, this also avoids some problems with optimizing
;;; collections of functions that are partially deleted.)
;;;
;;; This is called both before and after FIND-INITIAL-DFO runs. When called
;;; on a :INITIAL component, we don't care whether the caller and callee are in
;;; the same component. Afterward, we must stick with whatever component
;;; division we have chosen.
;;;
;;; Before attempting to convert a call, we see whether the function is
;;; supposed to be inline expanded. Call conversion proceeds as before
;;; after any expansion.
;;;
;;; We bind *Compiler-Error-Context* to the node for the call so that
;;; warnings will get the right context.
(defun convert-call-if-possible (ref call)
  (declare (type ref ref) (type basic-combination call))
  (let* ((block (node-block call))
         (component (block-component block))
         (original-fun (ref-leaf ref)))
    (aver (functional-p original-fun))
    (unless (or (member (basic-combination-kind call) '(:local :error))
                (block-delete-p block)
                (eq (functional-kind (block-home-lambda block)) :deleted)
                (member (functional-kind original-fun)
                        '(:top-level-xep :deleted))
                (not (or (eq (component-kind component) :initial)
                         (eq (block-component
                              (node-block
                               (lambda-bind (main-entry original-fun))))
                             component))))
      (let ((fun (if (external-entry-point-p original-fun)
                     (functional-entry-function original-fun)
                     original-fun))
            (*compiler-error-context* call))

        (when (and (eq (functional-inlinep fun) :inline)
                   (rest (leaf-refs original-fun)))
          (setq fun (maybe-expand-local-inline fun ref call)))

        (aver (member (functional-kind fun)
                      '(nil :escape :cleanup :optional)))
        (cond ((mv-combination-p call)
               (convert-mv-call ref call fun))
              ((lambda-p fun)
               (convert-lambda-call ref call fun))
              (t
               (convert-hairy-call ref call fun))))))

  (values))

;;; Attempt to convert a multiple-value call. The only interesting
;;; case is a call to a function that Looks-Like-An-MV-Bind, has
;;; exactly one reference and no XEP, and is called with one values
;;; continuation.
;;;
;;; We change the call to be to the last optional entry point and
;;; change the call to be local. Due to our preconditions, the call
;;; should eventually be converted to a let, but we can't do that now,
;;; since there may be stray references to the e-p lambda due to
;;; optional defaulting code.
;;;
;;; We also use variable types for the called function to construct an
;;; assertion for the values continuation.
;;;
;;; See CONVERT-CALL for additional notes on MERGE-TAIL-SETS, etc.
(defun convert-mv-call (ref call fun)
  (declare (type ref ref) (type mv-combination call) (type functional fun))
  (when (and (looks-like-an-mv-bind fun)
             (not (functional-entry-function fun))
             (= (length (leaf-refs fun)) 1)
             (= (length (basic-combination-args call)) 1))
    (let ((ep (car (last (optional-dispatch-entry-points fun)))))
      (setf (basic-combination-kind call) :local)
      (pushnew ep (lambda-calls (node-home-lambda call)))
      (merge-tail-sets call ep)
      (change-ref-leaf ref ep)

      (assert-continuation-type
       (first (basic-combination-args call))
       (make-values-type :optional (mapcar #'leaf-type (lambda-vars ep))
                         :rest *universal-type*))))
  (values))

;;; Attempt to convert a call to a lambda. If the number of args is
;;; wrong, we give a warning and mark the call as :ERROR to remove it
;;; from future consideration. If the argcount is O.K. then we just
;;; convert it.
(defun convert-lambda-call (ref call fun)
  (declare (type ref ref) (type combination call) (type clambda fun))
  (let ((nargs (length (lambda-vars fun)))
        (call-args (length (combination-args call))))
    (cond ((= call-args nargs)
           (convert-call ref call fun))
          (t
           ;; FIXME: ANSI requires in "3.2.5 Exceptional Situations in the
           ;; Compiler" that calling a function with "the wrong number of
           ;; arguments" be only a STYLE-ERROR. I think, though, that this
           ;; should only apply when the number of arguments is inferred
           ;; from a previous definition. If the number of arguments
           ;; is DECLAIMed, surely calling with the wrong number is a
           ;; real WARNING. As long as SBCL continues to use CMU CL's
           ;; non-ANSI DEFUN-is-a-DECLAIM policy, we're in violation here,
           ;; but as long as we continue to use that policy, that's the
           ;; not our biggest problem.:-| When we fix that policy, this
           ;; should come back into compliance. (So fix that policy!)
           ;;   ..but..
           ;; FIXME, continued: Except that section "3.2.2.3 Semantic
           ;; Constraints" says that if it's within the same file, it's
           ;; wrong. And we're in locall.lisp here, so it's probably
           ;; (haven't checked this..) a call to something in the same
           ;; file. So maybe it deserves a full warning anyway.
           (compiler-warning
            "function called with ~R argument~:P, but wants exactly ~R"
            call-args nargs)
           (setf (basic-combination-kind call) :error)))))
\f
;;;; optional, more and keyword calls

;;; This is similar to CONVERT-LAMBDA-CALL, but deals with
;;; OPTIONAL-DISPATCHes. If only fixed args are supplied, then convert
;;; a call to the correct entry point. If &KEY args are supplied, then
;;; dispatch to a subfunction. We don't convert calls to functions
;;; that have a &MORE (or &REST) arg.
(defun convert-hairy-call (ref call fun)
  (declare (type ref ref) (type combination call)
           (type optional-dispatch fun))
  (let ((min-args (optional-dispatch-min-args fun))
        (max-args (optional-dispatch-max-args fun))
        (call-args (length (combination-args call))))
    (cond ((< call-args min-args)
           ;; FIXME: See FIXME note at the previous
           ;; wrong-number-of-arguments warnings in this file.
           (compiler-warning
            "function called with ~R argument~:P, but wants at least ~R"
            call-args min-args)
           (setf (basic-combination-kind call) :error))
          ((<= call-args max-args)
           (convert-call ref call
                         (elt (optional-dispatch-entry-points fun)
                              (- call-args min-args))))
          ((optional-dispatch-more-entry fun)
           (convert-more-call ref call fun))
          (t
           ;; FIXME: See FIXME note at the previous
           ;; wrong-number-of-arguments warnings in this file.
           (compiler-warning
            "function called with ~R argument~:P, but wants at most ~R"
            call-args max-args)
           (setf (basic-combination-kind call) :error))))
  (values))

;;; This function is used to convert a call to an entry point when complex
;;; transformations need to be done on the original arguments. Entry is the
;;; entry point function that we are calling. Vars is a list of variable names
;;; which are bound to the original call arguments. Ignores is the subset of
;;; Vars which are ignored. Args is the list of arguments to the entry point
;;; function.
;;;
;;; In order to avoid gruesome graph grovelling, we introduce a new function
;;; that rearranges the arguments and calls the entry point. We analyze the
;;; new function and the entry point immediately so that everything gets
;;; converted during the single pass.
(defun convert-hairy-fun-entry (ref call entry vars ignores args)
  (declare (list vars ignores args) (type ref ref) (type combination call)
           (type clambda entry))
  (let ((new-fun
         (with-ir1-environment call
           (ir1-convert-lambda
            `(lambda ,vars
               (declare (ignorable . ,ignores))
               (%funcall ,entry . ,args))))))
    (convert-call ref call new-fun)
    (dolist (ref (leaf-refs entry))
      (convert-call-if-possible ref (continuation-dest (node-cont ref))))))

;;; Use CONVERT-HAIRY-FUN-ENTRY to convert a &MORE-arg call to a known
;;; function into a local call to the MAIN-ENTRY.
;;;
;;; First we verify that all keywords are constant and legal. If there
;;; aren't, then we warn the user and don't attempt to convert the call.
;;;
;;; We massage the supplied &KEY arguments into the order expected
;;; by the main entry. This is done by binding all the arguments to
;;; the keyword call to variables in the introduced lambda, then
;;; passing these values variables in the correct order when calling
;;; the main entry. Unused arguments (such as the keywords themselves)
;;; are discarded simply by not passing them along.
;;;
;;; If there is a &REST arg, then we bundle up the args and pass them
;;; to LIST.
(defun convert-more-call (ref call fun)
  (declare (type ref ref) (type combination call) (type optional-dispatch fun))
  (let* ((max (optional-dispatch-max-args fun))
         (arglist (optional-dispatch-arglist fun))
         (args (combination-args call))
         (more (nthcdr max args))
         (flame (policy call (or (> speed inhibit-warnings)
                                 (> space inhibit-warnings))))
         (loser nil)
         (temps (make-gensym-list max))
         (more-temps (make-gensym-list (length more))))
    (collect ((ignores)
              (supplied)
              (key-vars))

      (dolist (var arglist)
        (let ((info (lambda-var-arg-info var)))
          (when info
            (ecase (arg-info-kind info)
              (:keyword
               (key-vars var))
              ((:rest :optional))
              ((:more-context :more-count)
               (compiler-warning "can't local-call functions with &MORE args")
               (setf (basic-combination-kind call) :error)
               (return-from convert-more-call))))))

      (when (optional-dispatch-keyp fun)
        (when (oddp (length more))
          (compiler-warning "function called with odd number of ~
                             arguments in keyword portion")

          (setf (basic-combination-kind call) :error)
          (return-from convert-more-call))

        (do ((key more (cddr key))
             (temp more-temps (cddr temp)))
            ((null key))
          (let ((cont (first key)))
            (unless (constant-continuation-p cont)
              (when flame
                (compiler-note "non-constant keyword in keyword call"))
              (setf (basic-combination-kind call) :error)
              (return-from convert-more-call))

            (let ((name (continuation-value cont))
                  (dummy (first temp))
                  (val (second temp)))
              (dolist (var (key-vars)
                           (progn
                             (ignores dummy val)
                             (setq loser name)))
                (let ((info (lambda-var-arg-info var)))
                  (when (eq (arg-info-key info) name)
                    (ignores dummy)
                    (supplied (cons var val))
                    (return)))))))

        (when (and loser (not (optional-dispatch-allowp fun)))
          (compiler-warning "function called with unknown argument keyword ~S"
                            loser)
          (setf (basic-combination-kind call) :error)
          (return-from convert-more-call)))

      (collect ((call-args))
        (do ((var arglist (cdr var))
             (temp temps (cdr temp)))
            (())
          (let ((info (lambda-var-arg-info (car var))))
            (if info
                (ecase (arg-info-kind info)
                  (:optional
                   (call-args (car temp))
                   (when (arg-info-supplied-p info)
                     (call-args t)))
                  (:rest
                   (call-args `(list ,@more-temps))
                   (return))
                  (:keyword
                   (return)))
                (call-args (car temp)))))

        (dolist (var (key-vars))
          (let ((info (lambda-var-arg-info var))
                (temp (cdr (assoc var (supplied)))))
            (if temp
                (call-args temp)
                (call-args (arg-info-default info)))
            (when (arg-info-supplied-p info)
              (call-args (not (null temp))))))

        (convert-hairy-fun-entry ref call (optional-dispatch-main-entry fun)
                                 (append temps more-temps)
                                 (ignores) (call-args)))))

  (values))
\f
;;;; LET conversion
;;;;
;;;; Converting to a LET has differing significance to various parts of the
;;;; compiler:
;;;; -- The body of a LET is spliced in immediately after the corresponding
;;;;    combination node, making the control transfer explicit and allowing
;;;;    LETs to be mashed together into a single block. The value of the LET is
;;;;    delivered directly to the original continuation for the call,
;;;;    eliminating the need to propagate information from the dummy result
;;;;    continuation.
;;;; -- As far as IR1 optimization is concerned, it is interesting in that
;;;;    there is only one expression that the variable can be bound to, and
;;;;    this is easily substitited for.
;;;; -- LETs are interesting to environment analysis and to the back end
;;;;    because in most ways a LET can be considered to be "the same function"
;;;;    as its home function.
;;;; -- LET conversion has dynamic scope implications, since control transfers
;;;;    within the same environment are local. In a local control transfer,
;;;;    cleanup code must be emitted to remove dynamic bindings that are no
;;;;    longer in effect.

;;; Set up the control transfer to the called lambda. We split the call
;;; block immediately after the call, and link the head of FUN to the call
;;; block. The successor block after splitting (where we return to) is
;;; returned.
;;;
;;; If the lambda is is a different component than the call, then we call
;;; JOIN-COMPONENTS. This only happens in block compilation before
;;; FIND-INITIAL-DFO.
(defun insert-let-body (fun call)
  (declare (type clambda fun) (type basic-combination call))
  (let* ((call-block (node-block call))
         (bind-block (node-block (lambda-bind fun)))
         (component (block-component call-block)))
    (let ((fun-component (block-component bind-block)))
      (unless (eq fun-component component)
        (aver (eq (component-kind component) :initial))
        (join-components component fun-component)))

    (let ((*current-component* component))
      (node-ends-block call))
    ;; FIXME: Use PROPER-LIST-OF-LENGTH-P here, and look for other
    ;; uses of '=.*length' which could also be converted to use
    ;; PROPER-LIST-OF-LENGTH-P.
    (aver (= (length (block-succ call-block)) 1))
    (let ((next-block (first (block-succ call-block))))
      (unlink-blocks call-block next-block)
      (link-blocks call-block bind-block)
      next-block)))

;;; Handle the environment semantics of LET conversion. We add the
;;; lambda and its LETs to lets for the CALL's home function. We merge
;;; the calls for FUN with the calls for the home function, removing
;;; FUN in the process. We also merge the Entries.
;;;
;;; We also unlink the function head from the component head and set
;;; COMPONENT-REANALYZE to true to indicate that the DFO should be
;;; recomputed.
(defun merge-lets (fun call)
  (declare (type clambda fun) (type basic-combination call))
  (let ((component (block-component (node-block call))))
    (unlink-blocks (component-head component) (node-block (lambda-bind fun)))
    (setf (component-lambdas component)
          (delete fun (component-lambdas component)))
    (setf (component-reanalyze component) t))
  (setf (lambda-call-lexenv fun) (node-lexenv call))
  (let ((tails (lambda-tail-set fun)))
    (setf (tail-set-functions tails)
          (delete fun (tail-set-functions tails))))
  (setf (lambda-tail-set fun) nil)
  (let* ((home (node-home-lambda call))
         (home-env (lambda-environment home)))
    (push fun (lambda-lets home))
    (setf (lambda-home fun) home)
    (setf (lambda-environment fun) home-env)

    (let ((lets (lambda-lets fun)))
      (dolist (let lets)
        (setf (lambda-home let) home)
        (setf (lambda-environment let) home-env))

      (setf (lambda-lets home) (nconc lets (lambda-lets home)))
      (setf (lambda-lets fun) ()))

    (setf (lambda-calls home)
            (delete fun (nunion (lambda-calls fun) (lambda-calls home))))
    (setf (lambda-calls fun) ())

    (setf (lambda-entries home)
          (nconc (lambda-entries fun) (lambda-entries home)))
    (setf (lambda-entries fun) ()))
  (values))

;;; Handle the value semantics of LET conversion. Delete FUN's return
;;; node, and change the control flow to transfer to NEXT-BLOCK
;;; instead. Move all the uses of the result continuation to CALL's
;;; CONT.
;;;
;;; If the actual continuation is only used by the LET call, then we
;;; intersect the type assertion on the dummy continuation with the
;;; assertion for the actual continuation; in all other cases
;;; assertions on the dummy continuation are lost.
;;;
;;; We also intersect the derived type of the CALL with the derived
;;; type of all the dummy continuation's uses. This serves mainly to
;;; propagate TRULY-THE through LETs.
(defun move-return-uses (fun call next-block)
  (declare (type clambda fun) (type basic-combination call)
           (type cblock next-block))
  (let* ((return (lambda-return fun))
         (return-block (node-block return)))
    (unlink-blocks return-block
                   (component-tail (block-component return-block)))
    (link-blocks return-block next-block)
    (unlink-node return)
    (delete-return return)
    (let ((result (return-result return))
          (cont (node-cont call))
          (call-type (node-derived-type call)))
      (when (eq (continuation-use cont) call)
        (assert-continuation-type cont (continuation-asserted-type result)))
      (unless (eq call-type *wild-type*)
        (do-uses (use result)
          (derive-node-type use call-type)))
      (substitute-continuation-uses cont result)))
  (values))

;;; Change all CONT for all the calls to FUN to be the start
;;; continuation for the bind node. This allows the blocks to be
;;; joined if the caller count ever goes to one.
(defun move-let-call-cont (fun)
  (declare (type clambda fun))
  (let ((new-cont (node-prev (lambda-bind fun))))
    (dolist (ref (leaf-refs fun))
      (let ((dest (continuation-dest (node-cont ref))))
        (delete-continuation-use dest)
        (add-continuation-use dest new-cont))))
  (values))

;;; We are converting FUN to be a LET when the call is in a non-tail
;;; position. Any previously tail calls in FUN are no longer tail
;;; calls, and must be restored to normal calls which transfer to
;;; NEXT-BLOCK (FUN's return point.) We can't do this by DO-USES on
;;; the RETURN-RESULT, because the return might have been deleted (if
;;; all calls were TR.)
;;;
;;; The called function might be an assignment in the case where we
;;; are currently converting that function. In steady-state,
;;; assignments never appear in the lambda-calls.
(defun unconvert-tail-calls (fun call next-block)
  (dolist (called (lambda-calls fun))
    (dolist (ref (leaf-refs called))
      (let ((this-call (continuation-dest (node-cont ref))))
        (when (and (node-tail-p this-call)
                   (eq (node-home-lambda this-call) fun))
          (setf (node-tail-p this-call) nil)
          (ecase (functional-kind called)
            ((nil :cleanup :optional)
             (let ((block (node-block this-call))
                   (cont (node-cont call)))
               (ensure-block-start cont)
               (unlink-blocks block (first (block-succ block)))
               (link-blocks block next-block)
               (delete-continuation-use this-call)
               (add-continuation-use this-call cont)))
            (:deleted)
            (:assignment
             (aver (eq called fun))))))))
  (values))

;;; Deal with returning from a LET or assignment that we are
;;; converting. FUN is the function we are calling, CALL is a call to
;;; FUN, and NEXT-BLOCK is the return point for a non-tail call, or
;;; NULL if call is a tail call.
;;;
;;; If the call is not a tail call, then we must do
;;; UNCONVERT-TAIL-CALLS, since a tail call is a call which returns
;;; its value out of the enclosing non-let function. When call is
;;; non-TR, we must convert it back to an ordinary local call, since
;;; the value must be delivered to the receiver of CALL's value.
;;;
;;; We do different things depending on whether the caller and callee
;;; have returns left:

;;; -- If the callee has no return we just do MOVE-LET-CALL-CONT. Either 
;;;    the function doesn't return, or all returns are via tail-recursive
;;;    local calls.
;;; -- If CALL is a non-tail call, or if both have returns, then we
;;;    delete the callee's return, move its uses to the call's result
;;;    continuation, and transfer control to the appropriate return point.
;;; -- If the callee has a return, but the caller doesn't, then we move the
;;;    return to the caller.
(defun move-return-stuff (fun call next-block)
  (declare (type clambda fun) (type basic-combination call)
           (type (or cblock null) next-block))
  (when next-block
    (unconvert-tail-calls fun call next-block))
  (let* ((return (lambda-return fun))
         (call-fun (node-home-lambda call))
         (call-return (lambda-return call-fun)))
    (cond ((not return))
          ((or next-block call-return)
           (unless (block-delete-p (node-block return))
             (move-return-uses fun call
                               (or next-block (node-block call-return)))))
          (t
           (aver (node-tail-p call))
           (setf (lambda-return call-fun) return)
           (setf (return-lambda return) call-fun))))
  (move-let-call-cont fun)
  (values))

;;; Actually do LET conversion. We call subfunctions to do most of the
;;; work. We change the CALL's cont to be the continuation heading the
;;; bind block, and also do REOPTIMIZE-CONTINUATION on the args and
;;; Cont so that let-specific IR1 optimizations get a chance. We blow
;;; away any entry for the function in *FREE-FUNCTIONS* so that nobody
;;; will create new reference to it.
(defun let-convert (fun call)
  (declare (type clambda fun) (type basic-combination call))
  (let ((next-block (if (node-tail-p call)
                        nil
                        (insert-let-body fun call))))
    (move-return-stuff fun call next-block)
    (merge-lets fun call)))

;;; Reoptimize all of Call's args and its result.
(defun reoptimize-call (call)
  (declare (type basic-combination call))
  (dolist (arg (basic-combination-args call))
    (when arg
      (reoptimize-continuation arg)))
  (reoptimize-continuation (node-cont call))
  (values))

;;; We also don't convert calls to named functions which appear in the
;;; initial component, delaying this until optimization. This
;;; minimizes the likelyhood that we well let-convert a function which
;;; may have references added due to later local inline expansion
(defun ok-initial-convert-p (fun)
  (not (and (leaf-name fun)
            (eq (component-kind
                 (block-component
                  (node-block (lambda-bind fun))))
                :initial))))

;;; This function is called when there is some reason to believe that
;;; the lambda Fun might be converted into a let. This is done after
;;; local call analysis, and also when a reference is deleted. We only
;;; convert to a let when the function is a normal local function, has
;;; no XEP, and is referenced in exactly one local call. Conversion is
;;; also inhibited if the only reference is in a block about to be
;;; deleted. We return true if we converted.
;;;
;;; These rules may seem unnecessarily restrictive, since there are
;;; some cases where we could do the return with a jump that don't
;;; satisfy these requirements. The reason for doing things this way
;;; is that it makes the concept of a LET much more useful at the
;;; level of IR1 semantics. The :ASSIGNMENT function kind provides
;;; another way to optimize calls to single-return/multiple call
;;; functions.
;;;
;;; We don't attempt to convert calls to functions that have an XEP,
;;; since we might be embarrassed later when we want to convert a
;;; newly discovered local call. Also, see OK-INITIAL-CONVERT-P.
(defun maybe-let-convert (fun)
  (declare (type clambda fun))
  (let ((refs (leaf-refs fun)))
    (when (and refs
               (null (rest refs))
               (member (functional-kind fun) '(nil :assignment))
               (not (functional-entry-function fun)))
      (let* ((ref-cont (node-cont (first refs)))
             (dest (continuation-dest ref-cont)))
        (when (and (basic-combination-p dest)
                   (eq (basic-combination-fun dest) ref-cont)
                   (eq (basic-combination-kind dest) :local)
                   (not (block-delete-p (node-block dest)))
                   (cond ((ok-initial-convert-p fun) t)
                         (t
                          (reoptimize-continuation ref-cont)
                          nil)))
          (unless (eq (functional-kind fun) :assignment)
            (let-convert fun dest))
          (reoptimize-call dest)
          (setf (functional-kind fun)
                (if (mv-combination-p dest) :mv-let :let))))
      t)))
\f
;;;; tail local calls and assignments

;;; Return T if there are no cleanups between BLOCK1 and BLOCK2, or if
;;; they definitely won't generate any cleanup code. Currently we
;;; recognize lexical entry points that are only used locally (if at
;;; all).
(defun only-harmless-cleanups (block1 block2)
  (declare (type cblock block1 block2))
  (or (eq block1 block2)
      (let ((cleanup2 (block-start-cleanup block2)))
        (do ((cleanup (block-end-cleanup block1)
                      (node-enclosing-cleanup (cleanup-mess-up cleanup))))
            ((eq cleanup cleanup2) t)
          (case (cleanup-kind cleanup)
            ((:block :tagbody)
             (unless (null (entry-exits (cleanup-mess-up cleanup)))
               (return nil)))
            (t (return nil)))))))

;;; If a potentially TR local call really is TR, then convert it to
;;; jump directly to the called function. We also call
;;; MAYBE-CONVERT-TO-ASSIGNMENT. The first value is true if we
;;; tail-convert. The second is the value of M-C-T-A. We can switch
;;; the succesor (potentially deleting the RETURN node) unless:
;;; -- The call has already been converted.
;;; -- The call isn't TR (some implicit MV PROG1.)
;;; -- The call is in an XEP (thus we might decide to make it non-tail 
;;;    so that we can use known return inside the component.)
;;; -- There is a change in the cleanup between the call in the return, 
;;;    so we might need to introduce cleanup code.
(defun maybe-convert-tail-local-call (call)
  (declare (type combination call))
  (let ((return (continuation-dest (node-cont call))))
    (aver (return-p return))
    (when (and (not (node-tail-p call))
               (immediately-used-p (return-result return) call)
               (not (eq (functional-kind (node-home-lambda call))
                        :external))
               (only-harmless-cleanups (node-block call)
                                       (node-block return)))
      (node-ends-block call)
      (let ((block (node-block call))
            (fun (combination-lambda call)))
        (setf (node-tail-p call) t)
        (unlink-blocks block (first (block-succ block)))
        (link-blocks block (node-block (lambda-bind fun)))
        (values t (maybe-convert-to-assignment fun))))))

;;; This is called when we believe it might make sense to convert Fun
;;; to an assignment. All this function really does is determine when
;;; a function with more than one call can still be combined with the
;;; calling function's environment. We can convert when:
;;; -- The function is a normal, non-entry function, and
;;; -- Except for one call, all calls must be tail recursive calls 
;;;    in the called function (i.e. are self-recursive tail calls)
;;; -- OK-INITIAL-CONVERT-P is true.
;;;
;;; There may be one outside call, and it need not be tail-recursive.
;;; Since all tail local calls have already been converted to direct
;;; transfers, the only control semantics needed are to splice in the
;;; body at the non-tail call. If there is no non-tail call, then we
;;; need only merge the environments. Both cases are handled by
;;; LET-CONVERT.
;;;
;;; ### It would actually be possible to allow any number of outside
;;; calls as long as they all return to the same place (i.e. have the
;;; same conceptual continuation.) A special case of this would be
;;; when all of the outside calls are tail recursive.
(defun maybe-convert-to-assignment (fun)
  (declare (type clambda fun))
  (when (and (not (functional-kind fun))
             (not (functional-entry-function fun)))
    (let ((non-tail nil)
          (call-fun nil))
      (when (and (dolist (ref (leaf-refs fun) t)
                   (let ((dest (continuation-dest (node-cont ref))))
                     (when (block-delete-p (node-block dest)) (return nil))
                     (let ((home (node-home-lambda ref)))
                       (unless (eq home fun)
                         (when call-fun (return nil))
                         (setq call-fun home))
                       (unless (node-tail-p dest)
                         (when (or non-tail (eq home fun)) (return nil))
                         (setq non-tail dest)))))
                 (ok-initial-convert-p fun))
        (setf (functional-kind fun) :assignment)
        (let-convert fun (or non-tail
                             (continuation-dest
                              (node-cont (first (leaf-refs fun))))))
        (when non-tail (reoptimize-call non-tail))
        t))))