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;;; Continuation-passing style (CPS) intermediate language (IL)
;; Copyright (C) 2013, 2014, 2015, 2017 Free Software Foundation, Inc.
;;;; This library is free software; you can redistribute it and/or
;;;; modify it under the terms of the GNU Lesser General Public
;;;; License as published by the Free Software Foundation; either
;;;; version 3 of the License, or (at your option) any later version.
;;;;
;;;; This library is distributed in the hope that it will be useful,
;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;;;; Lesser General Public License for more details.
;;;;
;;;; You should have received a copy of the GNU Lesser General Public
;;;; License along with this library; if not, write to the Free Software
;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
;;; Commentary:
;;;
;;; Loop invariant code motion (LICM) hoists terms that don't affect a
;;; loop out of the loop, so that the loop goes faster.
;;;
;;; Code:
(define-module (language cps licm)
#:use-module (ice-9 match)
#:use-module (srfi srfi-11)
#:use-module (language cps)
#:use-module (language cps utils)
#:use-module (language cps intmap)
#:use-module (language cps intset)
#:use-module (language cps effects-analysis)
#:use-module (language cps type-checks)
#:export (hoist-loop-invariant-code))
(define (find-exits scc succs)
(intset-fold (lambda (label exits)
(if (eq? empty-intset
(intset-subtract (intmap-ref succs label) scc))
exits
(intset-add exits label)))
scc
empty-intset))
(define (find-entry scc preds)
(trivial-intset (find-exits scc preds)))
(define (list->intset l)
(persistent-intset
(fold1 (lambda (i set) (intset-add! set i)) l empty-intset)))
(define (loop-invariant? label exp loop-vars loop-effects always-reached?)
(let ((fx (intmap-ref loop-effects label)))
(and
(not (causes-effect? fx &allocation))
(or always-reached?
(not (causes-effect? fx &type-check)))
(or (not (causes-effect? fx &write))
(intmap-fold (lambda (label fx* invariant?)
(and invariant?
(not (effect-clobbers? fx fx*))))
loop-effects #t))
(or (not (causes-effect? fx &read))
(intmap-fold (lambda (label fx* invariant?)
(and invariant?
(not (effect-clobbers? fx* fx))))
loop-effects #t))
(match exp
((or ($ $const) ($ $prim) ($ $closure)) #t)
(($ $prompt) #f) ;; ?
(($ $branch) #f)
(($ $primcall 'values #f) #f)
(($ $primcall name param args)
(and-map (lambda (arg) (not (intset-ref loop-vars arg)))
args))
(($ $values args)
(and-map (lambda (arg) (not (intset-ref loop-vars arg)))
args))))))
(define (hoist-one cps label cont preds
loop-vars loop-effects pre-header-label always-reached?)
(define (filter-loop-vars names vars)
(match (vector names vars)
(#((name . names) (var . vars))
(if (intset-ref loop-vars var)
(let-values (((names vars) (filter-loop-vars names vars)))
(values (cons name names) (cons var vars)))
(filter-loop-vars names vars)))
(_ (values '() '()))))
(define (adjoin-loop-vars loop-vars vars)
(fold1 (lambda (var loop-vars) (intset-add loop-vars var))
vars loop-vars))
(define (hoist-exp src exp def-names def-vars pre-header-label)
(let* ((hoisted-label pre-header-label)
(pre-header-label (fresh-label))
(hoisted-cont
(rewrite-cont (intmap-ref cps hoisted-label)
(($ $kargs names vars)
($kargs names vars
($continue pre-header-label src ,exp)))))
(pre-header-cont
(rewrite-cont (intmap-ref cps hoisted-label)
(($ $kargs _ _ term)
($kargs def-names def-vars ,term)))))
(values (intmap-add! (intmap-replace! cps hoisted-label hoisted-cont)
pre-header-label pre-header-cont)
pre-header-label)))
(define (hoist-call src exp req rest def-names def-vars pre-header-label)
(let* ((hoisted-label pre-header-label)
(receive-label (fresh-label))
(pre-header-label (fresh-label))
(hoisted-cont
(rewrite-cont (intmap-ref cps hoisted-label)
(($ $kargs names vars)
($kargs names vars
($continue receive-label src ,exp)))))
(receive-cont
(build-cont
($kreceive req rest pre-header-label)))
(pre-header-cont
(rewrite-cont (intmap-ref cps hoisted-label)
(($ $kargs _ _ term)
($kargs def-names def-vars ,term)))))
(values (intmap-add!
(intmap-add! (intmap-replace! cps hoisted-label hoisted-cont)
receive-label receive-cont)
pre-header-label pre-header-cont)
pre-header-label)))
(match cont
(($ $kargs names vars ($ $continue k src exp))
;; If k is a loop exit, it will be nullary.
(let-values (((names vars) (filter-loop-vars names vars)))
(match (intmap-ref cps k)
(($ $kargs def-names def-vars)
(cond
((not (loop-invariant? label exp loop-vars loop-effects
always-reached?))
(let* ((loop-vars (adjoin-loop-vars loop-vars def-vars))
(loop-vars (match exp
(($ $prompt escape? tag handler)
(match (intmap-ref cps handler)
(($ $kreceive arity kargs)
(match (intmap-ref cps kargs)
(($ $kargs names vars)
(adjoin-loop-vars loop-vars vars))))))
(_ loop-vars)))
(cont (build-cont
($kargs names vars
($continue k src ,exp))))
(always-reached?
(and always-reached?
(match exp
(($ $branch) #f)
(_ (not (causes-effect? (intmap-ref loop-effects label)
&type-check)))))))
(values cps cont loop-vars loop-effects
pre-header-label always-reached?)))
((trivial-intset (intmap-ref preds k))
(let-values
(((cps pre-header-label)
(hoist-exp src exp def-names def-vars pre-header-label))
((cont) (build-cont
($kargs names vars
($continue k src ($values ()))))))
(values cps cont loop-vars (intmap-remove loop-effects label)
pre-header-label always-reached?)))
(else
(let*-values
(((def-names def-vars)
(match (intmap-ref cps k)
(($ $kargs names vars) (values names vars))))
((loop-vars) (adjoin-loop-vars loop-vars def-vars))
((fresh-vars) (map (lambda (_) (fresh-var)) def-vars))
((cps pre-header-label)
(hoist-exp src exp def-names fresh-vars pre-header-label))
((cont) (build-cont
($kargs names vars
($continue k src ($values fresh-vars))))))
(values cps cont loop-vars (intmap-remove loop-effects label)
pre-header-label always-reached?)))))
(($ $kreceive ($ $arity req () rest) kargs)
(match (intmap-ref cps kargs)
(($ $kargs def-names def-vars)
(cond
((not (loop-invariant? label exp loop-vars loop-effects
always-reached?))
(let* ((loop-vars (adjoin-loop-vars loop-vars def-vars))
(cont (build-cont
($kargs names vars
($continue k src ,exp)))))
(values cps cont loop-vars loop-effects pre-header-label #f)))
((trivial-intset (intmap-ref preds k))
(let ((loop-effects
(intmap-remove (intmap-remove loop-effects label) k)))
(let-values
(((cps pre-header-label)
(hoist-call src exp req rest def-names def-vars
pre-header-label))
((cont) (build-cont
($kargs names vars
($continue kargs src ($values ()))))))
(values cps cont loop-vars loop-effects
pre-header-label always-reached?))))
(else
(let*-values
(((loop-vars) (adjoin-loop-vars loop-vars def-vars))
((fresh-vars) (map (lambda (_) (fresh-var)) def-vars))
((cps pre-header-label)
(hoist-call src exp req rest def-names fresh-vars
pre-header-label))
((cont) (build-cont
($kargs names vars
($continue kargs src
($values fresh-vars))))))
(values cps cont loop-vars loop-effects
pre-header-label always-reached?))))))))))
(($ $kreceive ($ $arity req () rest) kargs)
(values cps cont loop-vars loop-effects pre-header-label
always-reached?))))
(define (hoist-in-loop cps entry body-labels succs preds effects)
(let* ((interior-succs (intmap-map (lambda (label succs)
(intset-intersect succs body-labels))
succs))
(sorted-labels (compute-reverse-post-order interior-succs entry))
(header-label (fresh-label))
(header-cont (intmap-ref cps entry))
(loop-vars (match header-cont
(($ $kargs names vars) (list->intset vars))))
(loop-effects (persistent-intmap
(intset-fold
(lambda (label loop-effects)
(let ((label*
(if (eqv? label entry) header-label label))
(fx (intmap-ref effects label)))
(intmap-add! loop-effects label* fx)))
body-labels empty-intmap)))
(pre-header-label entry)
(pre-header-cont (match header-cont
(($ $kargs names vars term)
(let ((vars* (map (lambda (_) (fresh-var)) vars)))
(build-cont
($kargs names vars*
($continue header-label #f
($values vars*))))))))
(cps (intmap-add! cps header-label header-cont))
(cps (intmap-replace! cps pre-header-label pre-header-cont))
(to-visit (match sorted-labels
((head . tail)
(unless (eqv? head entry) (error "what?"))
(cons header-label tail)))))
(define (rename-back-edges cont)
(define (rename label) (if (eqv? label entry) header-label label))
(rewrite-cont cont
(($ $kargs names vars ($ $continue kf src ($ $branch kt exp)))
($kargs names vars
($continue (rename kf) src ($branch (rename kt) ,exp))))
(($ $kargs names vars ($ $continue k src exp))
($kargs names vars
($continue (rename k) src ,exp)))
(($ $kreceive ($ $arity req () rest) k)
($kreceive req rest (rename k)))))
(let lp ((cps cps) (to-visit to-visit)
(loop-vars loop-vars) (loop-effects loop-effects)
(pre-header-label pre-header-label) (always-reached? #t))
(match to-visit
(() cps)
((label . to-visit)
(call-with-values
(lambda ()
(hoist-one cps label (intmap-ref cps label) preds
loop-vars loop-effects
pre-header-label always-reached?))
(lambda (cps cont
loop-vars loop-effects pre-header-label always-reached?)
(lp (intmap-replace! cps label (rename-back-edges cont)) to-visit
loop-vars loop-effects pre-header-label always-reached?))))))))
(define (hoist-in-function kfun body cps)
(let* ((succs (compute-successors cps kfun))
(preds (invert-graph succs))
(loops (intmap-fold
(lambda (id scc loops)
(cond
((trivial-intset scc) loops)
((find-entry scc preds)
=> (lambda (entry) (intmap-add! loops entry scc)))
(else loops)))
(compute-strongly-connected-components succs kfun)
empty-intmap)))
(if (eq? empty-intset loops)
cps
(let ((effects (compute-effects/elide-type-checks
(intset-fold (lambda (label body-conts)
(intmap-add! body-conts label
(intmap-ref cps label)))
body empty-intmap))))
(persistent-intmap
(intmap-fold (lambda (entry scc cps)
(hoist-in-loop cps entry scc succs preds effects))
loops cps))))))
(define (hoist-loop-invariant-code cps)
(with-fresh-name-state cps
(intmap-fold hoist-in-function
(compute-reachable-functions cps)
cps)))
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