0.pre7.38:

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

;;;; This file implements the environment analysis phase for the
;;;; compiler. This phase annotates IR1 with a hierarchy environment
;;;; structures, determining the environment that each LAMBDA 
;;;; allocates its variables and finding what values are closed over
;;;; by each environment.

;;;; 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")

;;; Do environment analysis on the code in COMPONENT. This involves
;;; various things:
;;;  1. Make an ENVIRONMENT structure for each non-LET LAMBDA, assigning 
;;;     the LAMBDA-ENVIRONMENT for all LAMBDAs.
;;;  2. Find all values that need to be closed over by each environment.
;;;  3. Scan the blocks in the component closing over non-local-exit
;;;     continuations.
;;;  4. Delete all non-top-level functions with no references. This
;;;     should only get functions with non-NULL kinds, since normal
;;;     functions are deleted when their references go to zero. If
;;;     *BYTE-COMPILING*, then don't delete optional entries with no
;;;     references, since the byte interpreter wants to call entries
;;;     that the XEP doesn't.
(defun environment-analyze (component)
  (declare (type component component))
  (aver (every (lambda (x)
                 (eq (functional-kind x) :deleted))
               (component-new-functions component)))
  (setf (component-new-functions component) ())
  (dolist (fun (component-lambdas component))
    (reinit-lambda-environment fun))
  (dolist (fun (component-lambdas component))
    (compute-closure fun)
    (dolist (let (lambda-lets fun))
      (compute-closure let)))

  (find-non-local-exits component)
  (find-cleanup-points component)
  (tail-annotate component)

  (dolist (fun (component-lambdas component))
    (when (null (leaf-refs fun))
      (let ((kind (functional-kind fun)))
        (unless (or (eq kind :top-level)
                    (functional-has-external-references-p fun)
                    (and *byte-compiling* (eq kind :optional)))
          (aver (member kind '(:optional :cleanup :escape)))
          (setf (functional-kind fun) nil)
          (delete-functional fun)))))

  (values))

;;; This is to be called on a COMPONENT with top-level LAMBDAs before
;;; the compilation of the associated non-top-level code to detect
;;; closed over top-level variables. We just do COMPUTE-CLOSURE on all
;;; the lambdas. This will pre-allocate environments for all the
;;; functions with closed-over top-level variables. The post-pass will
;;; use the existing structure, rather than allocating a new one. We
;;; return true if we discover any possible closure vars.
(defun pre-environment-analyze-top-level (component)
  (declare (type component component))
  (let ((found-it nil))
    (dolist (lambda (component-lambdas component))
      (when (compute-closure lambda)
        (setq found-it t))
      (dolist (let (lambda-lets lambda))
        (when (compute-closure let)
          (setq found-it t))))
    found-it))

;;; This is like old CMU CL PRE-ENVIRONMENT-ANALYZE-TOP-LEVEL, except
;;;   (1) It's been brought into the post-0.7.0 world where the property
;;;       HAS-EXTERNAL-REFERENCES-P is orthogonal to the property of
;;;       being specialized/optimized for locall at top level.
;;;   (2) There's no return value, since we don't care whether we
;;;       find any possible closure variables.
;;;
;;; I wish I could find an explanation of why
;;; PRE-ENVIRONMENT-ANALYZE-TOP-LEVEL is important. The old CMU CL
;;; comments said
;;;     Called on component with top-level lambdas before the
;;;     compilation of the associated non-top-level code to detect
;;;     closed over top-level variables. We just do COMPUTE-CLOSURE on
;;;     all the lambdas. This will pre-allocate environments for all
;;;     the functions with closed-over top-level variables. The
;;;     post-pass will use the existing structure, rather than
;;;     allocating a new one. We return true if we discover any
;;;     possible closure vars.
;;; But that doesn't seem to explain why it's important. I do observe
;;; that when it's not done, compiler assertions occasionally fail. My
;;; tentative hypothesis is that other environment analysis expects to
;;; bottom out on the outermost enclosing thing, and (insert
;;; mysterious reason here) it's important to set up bottomed-out-here
;;; environments before anything else. -- WHN 2001-09-30
(defun preallocate-environments-for-top-levelish-lambdas (component)
  (dolist (clambda (component-lambdas component))
    (when (lambda-top-levelish-p clambda)
      (compute-closure clambda)))
  (values))

;;; If FUN has an environment, return it, otherwise assign an empty one.
(defun get-lambda-environment (fun)
  (declare (type clambda fun))
  (let* ((fun (lambda-home fun))
         (env (lambda-environment fun)))
    (or env
        (let ((res (make-environment :function fun)))
          (setf (lambda-environment fun) res)
          (dolist (letlambda (lambda-lets fun))
            ;; This assertion is to make explicit an
            ;; apparently-otherwise-undocumented property of existing
            ;; code: We never overwrite an old LAMBDA-ENVIRONMENT.
            ;; -- WHN 2001-09-30
            (aver (null (lambda-environment letlambda)))
            ;; I *think* this is true regardless of LAMBDA-KIND.
            ;; -- WHN 2001-09-30
            (aver (eql (lambda-home letlambda) fun))
            (setf (lambda-environment letlambda) res))
          res))))

;;; If FUN has no physical environment, assign one, otherwise clean up
;;; the old physical environment, removing/flagging variables that
;;; have no sets or refs. If a var has no references, we remove it
;;; from the closure. If it has no sets, we clear the INDIRECT flag.
;;; This is necessary because pre-analysis is done before
;;; optimization.
(defun reinit-lambda-environment (fun)
  (let ((old (lambda-environment (lambda-home fun))))
    (cond (old
           (setf (environment-closure old)
                 (delete-if #'(lambda (x)
                                (and (lambda-var-p x)
                                     (null (leaf-refs x))))
                            (environment-closure old)))
           (flet ((clear (fun)
                    (dolist (var (lambda-vars fun))
                      (unless (lambda-var-sets var)
                        (setf (lambda-var-indirect var) nil)))))
             (clear fun)
             (dolist (let (lambda-lets fun))
               (clear let))))
          (t
           (get-lambda-environment fun))))
  (values))

;;; Get NODE's environment, assigning one if necessary.
(defun get-node-environment (node)
  (declare (type node node))
  (get-lambda-environment (node-home-lambda node)))

;;; Find any variables in FUN with references outside of the home
;;; environment and close over them. If a closed over variable is set,
;;; then we set the INDIRECT flag so that we will know the closed over
;;; value is really a pointer to the value cell. We also warn about
;;; unreferenced variables here, just because it's a convenient place
;;; to do it. We return true if we close over anything.
(defun compute-closure (fun)
  (declare (type clambda fun))
  (let ((env (get-lambda-environment fun))
        (did-something nil))
    (note-unreferenced-vars fun)
    (dolist (var (lambda-vars fun))
      (dolist (ref (leaf-refs var))
        (let ((ref-env (get-node-environment ref)))
          (unless (eq ref-env env)
            (when (lambda-var-sets var)
              (setf (lambda-var-indirect var) t))
            (setq did-something t)
            (close-over var ref-env env))))
      (dolist (set (basic-var-sets var))
        (let ((set-env (get-node-environment set)))
          (unless (eq set-env env)
            (setq did-something t)
            (setf (lambda-var-indirect var) t)
            (close-over var set-env env)))))
    did-something))

;;; Make sure that THING is closed over in REF-ENV and in all
;;; environments for the functions that reference REF-ENV's function
;;; (not just calls.) HOME-ENV is THING's home environment. When we
;;; reach the home environment, we stop propagating the closure.
(defun close-over (thing ref-env home-env)
  (declare (type environment ref-env home-env))
  (cond ((eq ref-env home-env))
        ((member thing (environment-closure ref-env)))
        (t
         (push thing (environment-closure ref-env))
         (dolist (call (leaf-refs (environment-function ref-env)))
           (close-over thing (get-node-environment call) home-env))))
  (values))
\f
;;;; non-local exit

;;; Insert the entry stub before the original exit target, and add a
;;; new entry to the ENVIRONMENT-NLX-INFO. The %NLX-ENTRY call in the
;;; stub is passed the NLX-INFO as an argument so that the back end
;;; knows what entry is being done.
;;;
;;; The link from the EXIT block to the entry stub is changed to be a
;;; link to the component head. Similarly, the EXIT block is linked to
;;; the component tail. This leaves the entry stub reachable, but
;;; makes the flow graph less confusing to flow analysis.
;;;
;;; If a CATCH or an UNWIND-protect, then we set the LEXENV for the
;;; last node in the cleanup code to be the enclosing environment, to
;;; represent the fact that the binding was undone as a side-effect of
;;; the exit. This will cause a lexical exit to be broken up if we are
;;; actually exiting the scope (i.e. a BLOCK), and will also do any
;;; other cleanups that may have to be done on the way.
(defun insert-nlx-entry-stub (exit env)
  (declare (type environment env) (type exit exit))
  (let* ((exit-block (node-block exit))
         (next-block (first (block-succ exit-block)))
         (cleanup (entry-cleanup (exit-entry exit)))
         (info (make-nlx-info :cleanup cleanup
                              :continuation (node-cont exit)))
         (entry (exit-entry exit))
         (new-block (insert-cleanup-code exit-block next-block
                                         entry
                                         `(%nlx-entry ',info)
                                         (entry-cleanup entry)))
         (component (block-component new-block)))
    (unlink-blocks exit-block new-block)
    (link-blocks exit-block (component-tail component))
    (link-blocks (component-head component) new-block)

    (setf (nlx-info-target info) new-block)
    (push info (environment-nlx-info env))
    (push info (cleanup-nlx-info cleanup))
    (when (member (cleanup-kind cleanup) '(:catch :unwind-protect))
      (setf (node-lexenv (block-last new-block))
            (node-lexenv entry))))

  (values))

;;; Do stuff necessary to represent a non-local exit from the node
;;; EXIT into ENV. This is called for each non-local exit node, of
;;; which there may be several per exit continuation. This is what we
;;; do:
;;; -- If there isn't any NLX-Info entry in the environment, make
;;;    an entry stub, otherwise just move the exit block link to
;;;    the component tail.
;;; -- Close over the NLX-Info in the exit environment.
;;; -- If the exit is from an :Escape function, then substitute a
;;;    constant reference to NLX-Info structure for the escape
;;;    function reference. This will cause the escape function to
;;;    be deleted (although not removed from the DFO.)  The escape
;;;    function is no longer needed, and we don't want to emit code
;;;    for it. We then also change the %NLX-ENTRY call to use the
;;;    NLX continuation so that there will be a use to represent
;;;    the NLX use.
(defun note-non-local-exit (env exit)
  (declare (type environment env) (type exit exit))
  (let ((entry (exit-entry exit))
        (cont (node-cont exit))
        (exit-fun (node-home-lambda exit)))

    (if (find-nlx-info entry cont)
        (let ((block (node-block exit)))
          (aver (= (length (block-succ block)) 1))
          (unlink-blocks block (first (block-succ block)))
          (link-blocks block (component-tail (block-component block))))
        (insert-nlx-entry-stub exit env))

    (let ((info (find-nlx-info entry cont)))
      (aver info)
      (close-over info (node-environment exit) env)
      (when (eq (functional-kind exit-fun) :escape)
        (mapc #'(lambda (x)
                  (setf (node-derived-type x) *wild-type*))
              (leaf-refs exit-fun))
        (substitute-leaf (find-constant info) exit-fun)
        (let ((node (block-last (nlx-info-target info))))
          (delete-continuation-use node)
          (add-continuation-use node (nlx-info-continuation info))))))

  (values))

;;; Iterate over the EXITs in COMPONENT, calling NOTE-NON-LOCAL-EXIT
;;; when we find a block that ends in a non-local EXIT node. We also
;;; ensure that all EXIT nodes are either non-local or degenerate by
;;; calling IR1-OPTIMIZE-EXIT on local exits. This makes life simpler
;;; for later phases.
(defun find-non-local-exits (component)
  (declare (type component component))
  (dolist (lambda (component-lambdas component))
    (dolist (entry (lambda-entries lambda))
      (dolist (exit (entry-exits entry))
        (let ((target-env (node-environment entry)))
          (if (eq (node-environment exit) target-env)
              (maybe-delete-exit exit)
              (note-non-local-exit target-env exit))))))

  (values))
\f
;;;; cleanup emission

;;; Zoom up the cleanup nesting until we hit CLEANUP1, accumulating
;;; cleanup code as we go. When we are done, convert the cleanup code
;;; in an implicit MV-PROG1. We have to force local call analysis of
;;; new references to UNWIND-PROTECT cleanup functions. If we don't
;;; actually have to do anything, then we don't insert any cleanup
;;; code.
;;;
;;; If we do insert cleanup code, we check that BLOCK1 doesn't end in
;;; a "tail" local call.
;;;
;;; We don't need to adjust the ending cleanup of the cleanup block,
;;; since the cleanup blocks are inserted at the start of the DFO, and
;;; are thus never scanned.
(defun emit-cleanups (block1 block2)
  (declare (type cblock block1 block2))
  (collect ((code)
            (reanalyze-funs))
    (let ((cleanup2 (block-start-cleanup block2)))
      (do ((cleanup (block-end-cleanup block1)
                    (node-enclosing-cleanup (cleanup-mess-up cleanup))))
          ((eq cleanup cleanup2))
        (let* ((node (cleanup-mess-up cleanup))
               (args (when (basic-combination-p node)
                       (basic-combination-args node))))
          (ecase (cleanup-kind cleanup)
            (:special-bind
             (code `(%special-unbind ',(continuation-value (first args)))))
            (:catch
             (code `(%catch-breakup)))
            (:unwind-protect
             (code `(%unwind-protect-breakup))
             (let ((fun (ref-leaf (continuation-use (second args)))))
               (reanalyze-funs fun)
               (code `(%funcall ,fun))))
            ((:block :tagbody)
             (dolist (nlx (cleanup-nlx-info cleanup))
               (code `(%lexical-exit-breakup ',nlx)))))))

      (when (code)
        (aver (not (node-tail-p (block-last block1))))
        (insert-cleanup-code block1 block2
                             (block-last block1)
                             `(progn ,@(code)))
        (dolist (fun (reanalyze-funs))
          (local-call-analyze-1 fun)))))

  (values))

;;; Loop over the blocks in COMPONENT, calling EMIT-CLEANUPS when we
;;; see a successor in the same environment with a different cleanup.
;;; We ignore the cleanup transition if it is to a cleanup enclosed by
;;; the current cleanup, since in that case we are just messing up the
;;; environment, hence this is not the place to clean it.
(defun find-cleanup-points (component)
  (declare (type component component))
  (do-blocks (block1 component)
    (let ((env1 (block-environment block1))
          (cleanup1 (block-end-cleanup block1)))
      (dolist (block2 (block-succ block1))
        (when (block-start block2)
          (let ((env2 (block-environment block2))
                (cleanup2 (block-start-cleanup block2)))
            (unless (or (not (eq env2 env1))
                        (eq cleanup1 cleanup2)
                        (and cleanup2
                             (eq (node-enclosing-cleanup
                                  (cleanup-mess-up cleanup2))
                                 cleanup1)))
              (emit-cleanups block1 block2)))))))
  (values))

;;; Mark all tail-recursive uses of function result continuations with
;;; the corresponding TAIL-SET. Nodes whose type is NIL (i.e. don't
;;; return) such as calls to ERROR are never annotated as tail in
;;; order to preserve debugging information.
(defun tail-annotate (component)
  (declare (type component component))
  (dolist (fun (component-lambdas component))
    (let ((ret (lambda-return fun)))
      (when ret
        (let ((result (return-result ret)))
          (do-uses (use result)
            (when (and (immediately-used-p result use)
                     (or (not (eq (node-derived-type use) *empty-type*))
                         (not (basic-combination-p use))
                         (eq (basic-combination-kind use) :local)))
                (setf (node-tail-p use) t)))))))
  (values))