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Add simplification pass

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* module/Makefile.am:
* module/language/cps/compile-bytecode.scm:
* module/language/cps/simplify.scm: New pass.
This commit is contained in:
Andy Wingo 2014-01-10 22:50:12 +01:00
parent 305cccb43c
commit 22a79b55b8
3 changed files with 280 additions and 8 deletions
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3
module/Makefile.am
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@ -1,6 +1,6 @@
## Process this file with automake to produce Makefile.in.
##
## Copyright (C) 2009, 2010, 2011, 2012, 2013 Free Software Foundation, Inc.
## Copyright (C) 2009, 2010, 2011, 2012, 2013, 2014 Free Software Foundation, Inc.
##
## This file is part of GUILE.
##
@ -130,6 +130,7 @@ CPS_LANG_SOURCES = \
language/cps/primitives.scm \
language/cps/reify-primitives.scm \
language/cps/slot-allocation.scm \
language/cps/simplify.scm \
language/cps/spec.scm \
language/cps/specialize-primcalls.scm \
language/cps/verify.scm

12
module/language/cps/compile-bytecode.scm
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@ -36,6 +36,7 @@
#:use-module (language cps elide-values)
#:use-module (language cps primitives)
#:use-module (language cps reify-primitives)
#:use-module (language cps simplify)
#:use-module (language cps slot-allocation)
#:use-module (language cps specialize-primcalls)
#:use-module (system vm assembler)
@ -59,27 +60,24 @@
;; aren't used, and thus shouldn't be consed.
(let* ((exp (run-pass exp eliminate-dead-code #:eliminate-dead-code? #t))
(exp (run-pass exp simplify #:simplify? #t))
(exp (run-pass exp contify #:contify? #t))
(exp (run-pass exp inline-constructors #:inline-constructors? #t))
(exp (run-pass exp specialize-primcalls #:specialize-primcalls? #t))
(exp (run-pass exp elide-values #:elide-values? #t))
(exp (run-pass exp eliminate-dead-code #:eliminate-dead-code? #t)))
(exp (run-pass exp eliminate-dead-code #:eliminate-dead-code? #t))
(exp (run-pass exp simplify #:simplify? #t)))
;; Passes that are needed:
;;
;; * Abort contification: turning abort primcalls into continuation
;; calls, and eliding prompts if possible.
;;
;; * Common subexpression elimination. Desperately needed. Requires
;; effects analysis.
;; * Common subexpression elimination. Desperately needed.
;;
;; * Loop peeling. Unrolls the first round through a loop if the
;; loop has effects that CSE can work on. Requires effects
;; analysis. When run before CSE, loop peeling is the equivalent
;; of loop-invariant code motion (LICM).
;;
;; * Generic simplification pass, to be run as needed. Used to
;; "clean up", both on the original raw input and after specific
;; optimization passes.
exp))

273
module/language/cps/simplify.scm Normal file
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@ -0,0 +1,273 @@
;;; Continuation-passing style (CPS) intermediate language (IL)
;; Copyright (C) 2013, 2014 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:
;;;
;;; The fundamental lambda calculus reductions, like beta and eta
;;; reduction and so on. Pretty lame currently.
;;;
;;; Code:
(define-module (language cps simplify)
#:use-module (ice-9 match)
#:use-module (srfi srfi-1)
#:use-module (srfi srfi-26)
#:use-module (language cps)
#:use-module (language cps dfg)
#:export (simplify))
;; Currently we just try to bypass all $values nodes that we can. This
;; is eta-reduction on continuations. Then we prune unused
;; continuations. Note that this pruning is just a quick clean-up; for
;; a real fixed-point pass that can eliminate unused loops, the
;; dead-code elimination pass is there for you. But DCE introduces new
;; nullary $values nodes (as replacements for expressions whose values
;; aren't used), making it useful for this pass to include its own
;; little pruner.
(define (compute-eta-reductions fun)
(let ((table (make-hash-table)))
(define (visit-cont cont)
(match cont
(($ $cont sym ($ $kargs names syms body))
(visit-term body sym syms))
(($ $cont sym ($ $kentry self tail clauses))
(for-each visit-cont clauses))
(($ $cont sym ($ $kclause arity body))
(visit-cont body))
(($ $cont sym _) #f)))
(define (visit-term term term-k term-args)
(match term
(($ $letk conts body)
(for-each visit-cont conts)
(visit-term body term-k term-args))
(($ $letrec names syms funs body)
(for-each visit-fun funs)
(visit-term body term-k term-args))
(($ $continue k src ($ $values args))
(when (equal? term-args args)
(hashq-set! table term-k k)))
(($ $continue k src (and fun ($ $fun)))
(visit-fun fun))
(($ $continue k src _)
#f)))
(define (visit-fun fun)
(match fun
(($ $fun src meta free body)
(visit-cont body))))
(visit-fun fun)
table))
(define (locally-prune-continuations fun dfg)
(let ((cfa (analyze-control-flow fun dfg)))
(define (must-visit-cont cont)
(or (visit-cont cont)
(error "cont must be reachable" cont)))
(define (visit-cont cont)
(match cont
(($ $cont sym cont)
(and (cfa-k-idx cfa sym #:default (lambda (k) #f))
(rewrite-cps-cont cont
(($ $kargs names syms body)
(sym ($kargs names syms ,(visit-term body))))
(($ $kentry self tail clauses)
(sym ($kentry self ,tail ,(visit-conts clauses))))
(($ $kclause arity body)
(sym ($kclause ,arity ,(must-visit-cont body))))
((or ($ $ktrunc) ($ $kif))
(sym ,cont)))))))
(define (visit-conts conts)
(filter-map visit-cont conts))
(define (visit-term term)
(match term
(($ $letk conts body)
(let ((body (visit-term body)))
(match (visit-conts conts)
(() body)
(conts (build-cps-term ($letk ,conts ,body))))))
(($ $letrec names syms funs body)
(build-cps-term
($letrec names syms funs ,(visit-term body))))
(($ $continue k src exp)
term)))
(rewrite-cps-exp fun
(($ $fun src meta free body)
($fun src meta free ,(must-visit-cont body))))))
(define (eta-reduce fun)
(let ((table (compute-eta-reductions fun))
(dfg (compute-dfg fun)))
(define (reduce* k scope values?)
(match (hashq-ref table k)
(#f k)
(k*
(if (and (continuation-bound-in? k* scope dfg)
(or values?
(match (lookup-cont k* (dfg-cont-table dfg))
(($ $kargs) #t)
(_ #f))))
(reduce* k* scope values?)
k))))
(define (reduce k scope)
(reduce* k scope #f))
(define (reduce-values k scope)
(reduce* k scope #t))
(define (visit-cont cont scope)
(rewrite-cps-cont cont
(($ $cont sym ($ $kargs names syms body))
(sym ($kargs names syms ,(visit-term body sym))))
(($ $cont sym ($ $kentry self tail clauses))
(sym ($kentry self ,tail ,(map (cut visit-cont <> sym) clauses))))
(($ $cont sym ($ $kclause arity body))
(sym ($kclause ,arity ,(visit-cont body sym))))
(($ $cont sym ($ $ktrunc ($ $arity req () rest () #f) kargs))
(sym ($ktrunc req rest (reduce kargs scope))))
(($ $cont sym ($ $kif kt kf))
(sym ($kif (reduce kt scope) (reduce kf scope))))))
(define (visit-term term scope)
(rewrite-cps-term term
(($ $letk conts body)
($letk ,(map (cut visit-cont <> scope) conts)
,(visit-term body scope)))
(($ $letrec names syms funs body)
($letrec names syms (map visit-fun funs)
,(visit-term body scope)))
(($ $continue k src ($ $values args))
($continue (reduce-values k scope) src ($values args)))
(($ $continue k src (and fun ($ $fun)))
($continue (reduce k scope) src ,(visit-fun fun)))
(($ $continue k src exp)
($continue (reduce k scope) src ,exp))))
(define (visit-fun fun)
(locally-prune-continuations
(rewrite-cps-exp fun
(($ $fun src meta free body)
($fun src meta free ,(visit-cont body #f))))
dfg))
(visit-fun fun)))
(define (compute-beta-reductions fun)
;; A continuation's body can be inlined in place of a $values
;; expression if the continuation is a $kargs. It should only be
;; inlined if it is used only once, and not recursively.
(let ((table (make-hash-table))
(dfg (compute-dfg fun)))
(define (visit-cont cont)
(match cont
(($ $cont sym ($ $kargs names syms body))
(visit-term body))
(($ $cont sym ($ $kentry self tail clauses))
(for-each visit-cont clauses))
(($ $cont sym ($ $kclause arity body))
(visit-cont body))
(($ $cont sym (or ($ $ktail) ($ $ktrunc) ($ $kif)))
#f)))
(define (visit-term term)
(match term
(($ $letk conts body)
(for-each visit-cont conts)
(visit-term body))
(($ $letrec names syms funs body)
(for-each visit-fun funs)
(visit-term body))
(($ $continue k src ($ $values args))
(match (lookup-cont k (dfg-cont-table dfg))
(($ $kargs names syms body)
(match (lookup-predecessors k dfg)
((_)
;; There is only one use, and it is this use. We assume
;; it's not recursive, as there would to be some other
;; use for control flow to reach this loop. Store the k
;; -> body mapping in the table. Also store the
;; substitutions for the variables bound by the inlined
;; continuation.
(for-each (cut hashq-set! table <> <>) syms args)
(hashq-set! table k body))
(_ #f)))
(_ #f)))
(($ $continue k src (and fun ($ $fun)))
(visit-fun fun))
(($ $continue k src _)
#f)))
(define (visit-fun fun)
(match fun
(($ $fun src meta free body)
(visit-cont body))))
(visit-fun fun)
table))
(define (beta-reduce fun)
(let ((table (compute-beta-reductions fun)))
(define (subst var)
(cond ((hashq-ref table var) => subst)
(else var)))
(define (must-visit-cont cont)
(or (visit-cont cont)
(error "continuation must not be inlined" cont)))
(define (visit-cont cont)
(match cont
(($ $cont sym cont)
(and (not (hashq-ref table sym))
(rewrite-cps-cont cont
(($ $kargs names syms body)
(sym ($kargs names syms ,(visit-term body))))
(($ $kentry self tail clauses)
(sym ($kentry self ,tail ,(map must-visit-cont clauses))))
(($ $kclause arity body)
(sym ($kclause ,arity ,(must-visit-cont body))))
((or ($ $ktrunc) ($ $kif))
(sym ,cont)))))))
(define (visit-term term)
(match term
(($ $letk conts body)
(match (filter-map visit-cont conts)
(() (visit-term body))
(conts (build-cps-term
($letk ,conts ,(visit-term body))))))
(($ $letrec names syms funs body)
(build-cps-term
($letrec names syms (map visit-fun funs)
,(visit-term body))))
(($ $continue k src exp)
(cond
((hashq-ref table k) => visit-term)
(else
(build-cps-term
($continue k src
,(match exp
((or ($ $void) ($ $const) ($ $prim)) exp)
(($ $fun) (visit-fun exp))
(($ $call proc args)
(let ((args (map subst args)))
(build-cps-exp ($call (subst proc) args))))
(($ $primcall name args)
(let ((args (map subst args)))
(build-cps-exp ($primcall name args))))
(($ $values args)
(let ((args (map subst args)))
(build-cps-exp ($values args))))
(($ $prompt escape? tag handler)
(build-cps-exp ($prompt escape? (subst tag) handler)))))))))))
(define (visit-fun fun)
(rewrite-cps-exp fun
(($ $fun src meta free body)
($fun src meta (map subst free) ,(must-visit-cont body)))))
(visit-fun fun)))
(define (simplify fun)
(eta-reduce (beta-reduce fun)))