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|
;;; Tree-IL partial evaluator
;; Copyright (C) 2011, 2012 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
(define-module (language tree-il peval)
#:use-module (language tree-il)
#:use-module (language tree-il primitives)
#:use-module (ice-9 vlist)
#:use-module (ice-9 match)
#:use-module (srfi srfi-1)
#:use-module (srfi srfi-9)
#:use-module (srfi srfi-11)
#:use-module (srfi srfi-26)
#:export (peval))
;;;
;;; Partial evaluation is Guile's most important source-to-source
;;; optimization pass. It performs copy propagation, dead code
;;; elimination, inlining, and constant folding, all while preserving
;;; the order of effects in the residual program.
;;;
;;; For more on partial evaluation, see William Cook’s excellent
;;; tutorial on partial evaluation at DSL 2011, called “Build your own
;;; partial evaluator in 90 minutes”[0].
;;;
;;; Our implementation of this algorithm was heavily influenced by
;;; Waddell and Dybvig's paper, "Fast and Effective Procedure Inlining",
;;; IU CS Dept. TR 484.
;;;
;;; [0] http://www.cs.utexas.edu/~wcook/tutorial/.
;;;
;; First, some helpers.
;;
(define-syntax *logging* (identifier-syntax #f))
;; For efficiency we define *logging* to inline to #f, so that the call
;; to log* gets optimized out. If you want to log, uncomment these
;; lines:
;;
;; (define %logging #f)
;; (define-syntax *logging* (identifier-syntax %logging))
;;
;; Then you can change %logging at runtime.
(define-syntax log
(syntax-rules (quote)
((log 'event arg ...)
(if (and *logging*
(or (eq? *logging* #t)
(memq 'event *logging*)))
(log* 'event arg ...)))))
(define (log* event . args)
(let ((pp (module-ref (resolve-interface '(ice-9 pretty-print))
'pretty-print)))
(pp `(log ,event . ,args))
(newline)
(values)))
(define-syntax-rule (let/ec k e e* ...)
(let ((tag (make-prompt-tag)))
(call-with-prompt
tag
(lambda ()
(let ((k (lambda args (apply abort-to-prompt tag args))))
e e* ...))
(lambda (_ res) res))))
(define (tree-il-any proc exp)
(let/ec k
(tree-il-fold (lambda (exp res)
(let ((res (proc exp)))
(if res (k res) #f)))
(lambda (exp res)
(let ((res (proc exp)))
(if res (k res) #f)))
(lambda (exp res) #f)
#f exp)))
(define (vlist-any proc vlist)
(let ((len (vlist-length vlist)))
(let lp ((i 0))
(and (< i len)
(or (proc (vlist-ref vlist i))
(lp (1+ i)))))))
(define (singly-valued-expression? exp)
(match exp
(($ <const>) #t)
(($ <lexical-ref>) #t)
(($ <void>) #t)
(($ <lexical-ref>) #t)
(($ <primitive-ref>) #t)
(($ <module-ref>) #t)
(($ <toplevel-ref>) #t)
(($ <primcall> _ (? singly-valued-primitive?)) #t)
(($ <primcall> _ 'values (val)) #t)
(($ <lambda>) #t)
(else #f)))
(define (truncate-values x)
"Discard all but the first value of X."
(if (singly-valued-expression? x)
x
(make-primcall (tree-il-src x) 'values (list x))))
;; Peval will do a one-pass analysis on the source program to determine
;; the set of assigned lexicals, and to identify unreferenced and
;; singly-referenced lexicals.
;;
(define-record-type <var>
(make-var name gensym refcount set?)
var?
(name var-name)
(gensym var-gensym)
(refcount var-refcount set-var-refcount!)
(set? var-set? set-var-set?!))
(define* (build-var-table exp #:optional (table vlist-null))
(tree-il-fold
(lambda (exp res)
(match exp
(($ <lexical-ref> src name gensym)
(let ((var (cdr (vhash-assq gensym res))))
(set-var-refcount! var (1+ (var-refcount var)))
res))
(_ res)))
(lambda (exp res)
(match exp
(($ <lambda-case> src req opt rest kw init gensyms body alt)
(fold (lambda (name sym res)
(vhash-consq sym (make-var name sym 0 #f) res))
res
(append req (or opt '()) (if rest (list rest) '())
(match kw
((aok? (kw name sym) ...) name)
(_ '())))
gensyms))
(($ <let> src names gensyms vals body)
(fold (lambda (name sym res)
(vhash-consq sym (make-var name sym 0 #f) res))
res names gensyms))
(($ <letrec> src in-order? names gensyms vals body)
(fold (lambda (name sym res)
(vhash-consq sym (make-var name sym 0 #f) res))
res names gensyms))
(($ <fix> src names gensyms vals body)
(fold (lambda (name sym res)
(vhash-consq sym (make-var name sym 0 #f) res))
res names gensyms))
(($ <lexical-set> src name gensym exp)
(set-var-set?! (cdr (vhash-assq gensym res)) #t)
res)
(_ res)))
(lambda (exp res) res)
table exp))
;; Counters are data structures used to limit the effort that peval
;; spends on particular inlining attempts. Each call site in the source
;; program is allocated some amount of effort. If peval exceeds the
;; effort counter while attempting to inline a call site, it aborts the
;; inlining attempt and residualizes a call instead.
;;
;; As there is a fixed number of call sites, that makes `peval' O(N) in
;; the number of call sites in the source program.
;;
;; Counters should limit the size of the residual program as well, but
;; currently this is not implemented.
;;
;; At the top level, before seeing any peval call, there is no counter,
;; because inlining will terminate as there is no recursion. When peval
;; sees a call at the top level, it will make a new counter, allocating
;; it some amount of effort and size.
;;
;; This top-level effort counter effectively "prints money". Within a
;; toplevel counter, no more effort is printed ex nihilo; for a nested
;; inlining attempt to proceed, effort must be transferred from the
;; toplevel counter to the nested counter.
;;
;; Via `data' and `prev', counters form a linked list, terminating in a
;; toplevel counter. In practice `data' will be the a pointer to the
;; source expression of the procedure being inlined.
;;
;; In this way peval can detect a recursive inlining attempt, by walking
;; back on the `prev' links looking for matching `data'. Recursive
;; counters receive a more limited effort allocation, as we don't want
;; to spend all of the effort for a toplevel inlining site on loops.
;; Also, recursive counters don't need a prompt at each inlining site:
;; either the call chain folds entirely, or it will be residualized at
;; its original call.
;;
(define-record-type <counter>
(%make-counter effort size continuation recursive? data prev)
counter?
(effort effort-counter)
(size size-counter)
(continuation counter-continuation)
(recursive? counter-recursive? set-counter-recursive?!)
(data counter-data)
(prev counter-prev))
(define (abort-counter c)
((counter-continuation c)))
(define (record-effort! c)
(let ((e (effort-counter c)))
(if (zero? (variable-ref e))
(abort-counter c)
(variable-set! e (1- (variable-ref e))))))
(define (record-size! c)
(let ((s (size-counter c)))
(if (zero? (variable-ref s))
(abort-counter c)
(variable-set! s (1- (variable-ref s))))))
(define (find-counter data counter)
(and counter
(if (eq? data (counter-data counter))
counter
(find-counter data (counter-prev counter)))))
(define* (transfer! from to #:optional
(effort (variable-ref (effort-counter from)))
(size (variable-ref (size-counter from))))
(define (transfer-counter! from-v to-v amount)
(let* ((from-balance (variable-ref from-v))
(to-balance (variable-ref to-v))
(amount (min amount from-balance)))
(variable-set! from-v (- from-balance amount))
(variable-set! to-v (+ to-balance amount))))
(transfer-counter! (effort-counter from) (effort-counter to) effort)
(transfer-counter! (size-counter from) (size-counter to) size))
(define (make-top-counter effort-limit size-limit continuation data)
(%make-counter (make-variable effort-limit)
(make-variable size-limit)
continuation
#t
data
#f))
(define (make-nested-counter continuation data current)
(let ((c (%make-counter (make-variable 0)
(make-variable 0)
continuation
#f
data
current)))
(transfer! current c)
c))
(define (make-recursive-counter effort-limit size-limit orig current)
(let ((c (%make-counter (make-variable 0)
(make-variable 0)
(counter-continuation orig)
#t
(counter-data orig)
current)))
(transfer! current c effort-limit size-limit)
c))
;; Operand structures allow bindings to be processed lazily instead of
;; eagerly. By doing so, hopefully we can get process them in a way
;; appropriate to their use contexts. Operands also prevent values from
;; being visited multiple times, wasting effort.
;;
;; TODO: Record value size in operand structure?
;;
(define-record-type <operand>
(%make-operand var sym visit source visit-count residualize?
copyable? residual-value constant-value)
operand?
(var operand-var)
(sym operand-sym)
(visit %operand-visit)
(source operand-source)
(visit-count operand-visit-count set-operand-visit-count!)
(residualize? operand-residualize? set-operand-residualize?!)
(copyable? operand-copyable? set-operand-copyable?!)
(residual-value operand-residual-value %set-operand-residual-value!)
(constant-value operand-constant-value set-operand-constant-value!))
(define* (make-operand var sym #:optional source visit)
;; Bind SYM to VAR, with value SOURCE. Bound operands are considered
;; copyable until we prove otherwise. If we have a source expression,
;; truncate it to one value. Copy propagation does not work on
;; multiply-valued expressions.
(let ((source (and=> source truncate-values)))
(%make-operand var sym visit source 0 #f (and source #t) #f #f)))
(define (make-bound-operands vars syms sources visit)
(map (lambda (x y z) (make-operand x y z visit)) vars syms sources))
(define (make-unbound-operands vars syms)
(map make-operand vars syms))
(define (set-operand-residual-value! op val)
(%set-operand-residual-value!
op
(match val
(($ <primcall> src 'values (first))
;; The continuation of a residualized binding does not need the
;; introduced `values' node, so undo the effects of truncation.
first)
(else
val))))
(define* (visit-operand op counter ctx #:optional effort-limit size-limit)
;; Peval is O(N) in call sites of the source program. However,
;; visiting an operand can introduce new call sites. If we visit an
;; operand outside a counter -- i.e., outside an inlining attempt --
;; this can lead to divergence. So, if we are visiting an operand to
;; try to copy it, and there is no counter, make a new one.
;;
;; This will only happen at most as many times as there are lexical
;; references in the source program.
(and (zero? (operand-visit-count op))
(dynamic-wind
(lambda ()
(set-operand-visit-count! op (1+ (operand-visit-count op))))
(lambda ()
(and (operand-source op)
(if (or counter (and (not effort-limit) (not size-limit)))
((%operand-visit op) (operand-source op) counter ctx)
(let/ec k
(define (abort) (k #f))
((%operand-visit op)
(operand-source op)
(make-top-counter effort-limit size-limit abort op)
ctx)))))
(lambda ()
(set-operand-visit-count! op (1- (operand-visit-count op)))))))
;; A helper for constant folding.
;;
(define (types-check? primitive-name args)
(case primitive-name
((values) #t)
((not pair? null? list? symbol? vector? struct?)
(= (length args) 1))
((eq? eqv? equal?)
(= (length args) 2))
;; FIXME: add more cases?
(else #f)))
(define* (peval exp #:optional (cenv (current-module)) (env vlist-null)
#:key
(operator-size-limit 40)
(operand-size-limit 20)
(value-size-limit 10)
(effort-limit 500)
(recursive-effort-limit 100))
"Partially evaluate EXP in compilation environment CENV, with
top-level bindings from ENV and return the resulting expression."
;; This is a simple partial evaluator. It effectively performs
;; constant folding, copy propagation, dead code elimination, and
;; inlining.
;; TODO:
;;
;; Propagate copies across toplevel bindings, if we can prove the
;; bindings to be immutable.
;;
;; Specialize lambda expressions with invariant arguments.
(define local-toplevel-env
;; The top-level environment of the module being compiled.
(let ()
(define (env-folder x env)
(match x
(($ <toplevel-define> _ name)
(vhash-consq name #t env))
(($ <seq> _ head tail)
(env-folder tail (env-folder head env)))
(_ env)))
(env-folder exp vlist-null)))
(define (local-toplevel? name)
(vhash-assq name local-toplevel-env))
;; gensym -> <var>
;; renamed-term -> original-term
;;
(define store (build-var-table exp))
(define (record-new-temporary! name sym refcount)
(set! store (vhash-consq sym (make-var name sym refcount #f) store)))
(define (lookup-var sym)
(let ((v (vhash-assq sym store)))
(if v (cdr v) (error "unbound var" sym (vlist->list store)))))
(define (fresh-gensyms vars)
(map (lambda (var)
(let ((new (gensym (string-append (symbol->string (var-name var))
"-"))))
(set! store (vhash-consq new var store))
new))
vars))
(define (assigned-lexical? sym)
(var-set? (lookup-var sym)))
(define (lexical-refcount sym)
(var-refcount (lookup-var sym)))
;; ORIG has been alpha-renamed to NEW. Analyze NEW and record a link
;; from it to ORIG.
;;
(define (record-source-expression! orig new)
(set! store (vhash-consq new (source-expression orig) store))
new)
;; Find the source expression corresponding to NEW. Used to detect
;; recursive inlining attempts.
;;
(define (source-expression new)
(let ((x (vhash-assq new store)))
(if x (cdr x) new)))
(define* (residualize-lexical op #:optional ctx val)
(log 'residualize op)
(set-operand-residualize?! op #t)
(if (eq? ctx 'value)
(set-operand-residual-value! op val))
(make-lexical-ref #f (var-name (operand-var op)) (operand-sym op)))
(define (fold-constants src name args ctx)
(define (apply-primitive name args)
;; todo: further optimize commutative primitives
(catch #t
(lambda ()
(call-with-values
(lambda ()
(apply (module-ref the-scm-module name) args))
(lambda results
(values #t results))))
(lambda _
(values #f '()))))
(define (make-values src values)
(match values
((single) single) ; 1 value
((_ ...) ; 0, or 2 or more values
(make-primcall src 'values values))))
(define (residualize-call)
(make-primcall src name args))
(cond
((every const? args)
(let-values (((success? values)
(apply-primitive name (map const-exp args))))
(log 'fold success? values name args)
(if success?
(case ctx
((effect) (make-void src))
((test)
;; Values truncation: only take the first
;; value.
(if (pair? values)
(make-const src (car values))
(make-values src '())))
(else
(make-values src (map (cut make-const src <>) values))))
(residualize-call))))
((and (eq? ctx 'effect) (types-check? name args))
(make-void #f))
(else
(residualize-call))))
(define (inline-values exp src names gensyms body)
(let loop ((exp exp))
(match exp
;; Some expression types are always singly-valued.
((or ($ <const>)
($ <void>)
($ <lambda>)
($ <lexical-ref>)
($ <toplevel-ref>)
($ <module-ref>)
($ <primitive-ref>)
($ <dynref>)
($ <lexical-set>) ; FIXME: these set! expressions
($ <toplevel-set>) ; could return zero values in
($ <toplevel-define>) ; the future
($ <module-set>) ;
($ <dynset>)) ;
(and (= (length names) 1)
(make-let src names gensyms (list exp) body)))
(($ <primcall> src (? singly-valued-primitive? name))
(and (= (length names) 1)
(make-let src names gensyms (list exp) body)))
;; Statically-known number of values.
(($ <primcall> src 'values vals)
(and (= (length names) (length vals))
(make-let src names gensyms vals body)))
;; Not going to copy code into both branches.
(($ <conditional>) #f)
;; Bail on other applications.
(($ <call>) #f)
(($ <primcall>) #f)
;; Bail on prompt and abort.
(($ <prompt>) #f)
(($ <abort>) #f)
;; Propagate to tail positions.
(($ <let> src names gensyms vals body)
(let ((body (loop body)))
(and body
(make-let src names gensyms vals body))))
(($ <letrec> src in-order? names gensyms vals body)
(let ((body (loop body)))
(and body
(make-letrec src in-order? names gensyms vals body))))
(($ <fix> src names gensyms vals body)
(let ((body (loop body)))
(and body
(make-fix src names gensyms vals body))))
(($ <let-values> src exp
($ <lambda-case> src2 req opt rest kw inits gensyms body #f))
(let ((body (loop body)))
(and body
(make-let-values src exp
(make-lambda-case src2 req opt rest kw
inits gensyms body #f)))))
(($ <dynwind> src winder pre body post unwinder)
(let ((body (loop body)))
(and body
(make-dynwind src winder pre body post unwinder))))
(($ <dynlet> src fluids vals body)
(let ((body (loop body)))
(and body
(make-dynlet src fluids vals body))))
(($ <seq> src head tail)
(let ((tail (loop tail)))
(and tail (make-seq src head tail)))))))
(define (constant-expression? x)
;; Return true if X is constant, for the purposes of copying or
;; elision---i.e., if it is known to have no effects, does not
;; allocate storage for a mutable object, and does not access
;; mutable data (like `car' or toplevel references).
(let loop ((x x))
(match x
(($ <void>) #t)
(($ <const>) #t)
(($ <lambda>) #t)
(($ <lambda-case> _ req opt rest kw inits syms body alternate)
(and (not (any assigned-lexical? syms))
(every loop inits) (loop body)
(or (not alternate) (loop alternate))))
(($ <lexical-ref> _ _ gensym)
(not (assigned-lexical? gensym)))
(($ <primitive-ref>) #t)
(($ <conditional> _ condition subsequent alternate)
(and (loop condition) (loop subsequent) (loop alternate)))
(($ <primcall> _ 'values exps)
(and (not (null? exps))
(every loop exps)))
(($ <primcall> _ name args)
(and (effect-free-primitive? name)
(not (constructor-primitive? name))
(types-check? name args)
(if (accessor-primitive? name)
(every const? args)
(every loop args))))
(($ <call> _ ($ <lambda> _ _ body) args)
(and (loop body) (every loop args)))
(($ <seq> _ head tail)
(and (loop head) (loop tail)))
(($ <let> _ _ syms vals body)
(and (not (any assigned-lexical? syms))
(every loop vals) (loop body)))
(($ <letrec> _ _ _ syms vals body)
(and (not (any assigned-lexical? syms))
(every loop vals) (loop body)))
(($ <fix> _ _ _ vals body)
(and (every loop vals) (loop body)))
(($ <let-values> _ exp body)
(and (loop exp) (loop body)))
(($ <prompt> _ tag body handler)
(and (loop tag) (loop body) (loop handler)))
(_ #f))))
(define (prune-bindings ops in-order? body counter ctx build-result)
;; This helper handles both `let' and `letrec'/`fix'. In the latter
;; cases we need to make sure that if referenced binding A needs
;; as-yet-unreferenced binding B, that B is processed for value.
;; Likewise if C, when processed for effect, needs otherwise
;; unreferenced D, then D needs to be processed for value too.
;;
(define (referenced? op)
;; When we visit lambdas in operator context, we just copy them,
;; as we will process their body later. However this does have
;; the problem that any free var referenced by the lambda is not
;; marked as needing residualization. Here we hack around this
;; and treat all bindings as referenced if we are in operator
;; context.
(or (eq? ctx 'operator) (operand-residualize? op)))
;; values := (op ...)
;; effects := (op ...)
(define (residualize values effects)
;; Note, values and effects are reversed.
(cond
(in-order?
(let ((values (filter operand-residual-value ops)))
(if (null? values)
body
(build-result (map (compose var-name operand-var) values)
(map operand-sym values)
(map operand-residual-value values)
body))))
(else
(let ((body
(if (null? effects)
body
(let ((effect-vals (map operand-residual-value effects)))
(list->seq #f (reverse (cons body effect-vals)))))))
(if (null? values)
body
(let ((values (reverse values)))
(build-result (map (compose var-name operand-var) values)
(map operand-sym values)
(map operand-residual-value values)
body)))))))
;; old := (bool ...)
;; values := (op ...)
;; effects := ((op . value) ...)
(let prune ((old (map referenced? ops)) (values '()) (effects '()))
(let lp ((ops* ops) (values values) (effects effects))
(cond
((null? ops*)
(let ((new (map referenced? ops)))
(if (not (equal? new old))
(prune new values '())
(residualize values
(map (lambda (op val)
(set-operand-residual-value! op val)
op)
(map car effects) (map cdr effects))))))
(else
(let ((op (car ops*)))
(cond
((memq op values)
(lp (cdr ops*) values effects))
((operand-residual-value op)
(lp (cdr ops*) (cons op values) effects))
((referenced? op)
(set-operand-residual-value! op (visit-operand op counter 'value))
(lp (cdr ops*) (cons op values) effects))
(else
(lp (cdr ops*)
values
(let ((effect (visit-operand op counter 'effect)))
(if (void? effect)
effects
(acons op effect effects))))))))))))
(define (small-expression? x limit)
(let/ec k
(tree-il-fold
(lambda (x res) ; leaf
(1+ res))
(lambda (x res) ; down
(1+ res))
(lambda (x res) ; up
(if (< res limit)
res
(k #f)))
0 x)
#t))
(define (extend-env sym op env)
(vhash-consq (operand-sym op) op (vhash-consq sym op env)))
(let loop ((exp exp)
(env vlist-null) ; vhash of gensym -> <operand>
(counter #f) ; inlined call stack
(ctx 'values)) ; effect, value, values, test, operator, or call
(define (lookup var)
(cond
((vhash-assq var env) => cdr)
(else (error "unbound var" var))))
(define (visit exp ctx)
(loop exp env counter ctx))
(define (for-value exp) (visit exp 'value))
(define (for-values exp) (visit exp 'values))
(define (for-test exp) (visit exp 'test))
(define (for-effect exp) (visit exp 'effect))
(define (for-call exp) (visit exp 'call))
(define (for-tail exp) (visit exp ctx))
(if counter
(record-effort! counter))
(log 'visit ctx (and=> counter effort-counter)
(unparse-tree-il exp))
(match exp
(($ <const>)
(case ctx
((effect) (make-void #f))
(else exp)))
(($ <void>)
(case ctx
((test) (make-const #f #t))
(else exp)))
(($ <lexical-ref> _ _ gensym)
(log 'begin-copy gensym)
(let ((op (lookup gensym)))
(cond
((eq? ctx 'effect)
(log 'lexical-for-effect gensym)
(make-void #f))
((eq? ctx 'call)
;; Don't propagate copies if we are residualizing a call.
(log 'residualize-lexical-call gensym op)
(residualize-lexical op))
((var-set? (operand-var op))
;; Assigned lexicals don't copy-propagate.
(log 'assigned-var gensym op)
(residualize-lexical op))
((not (operand-copyable? op))
;; We already know that this operand is not copyable.
(log 'not-copyable gensym op)
(residualize-lexical op))
((and=> (operand-constant-value op)
(lambda (x) (or (const? x) (void? x) (primitive-ref? x))))
;; A cache hit.
(let ((val (operand-constant-value op)))
(log 'memoized-constant gensym val)
(for-tail val)))
((visit-operand op counter (if (eq? ctx 'values) 'value ctx)
recursive-effort-limit operand-size-limit)
=>
;; If we end up deciding to residualize this value instead of
;; copying it, save that residualized value.
(lambda (val)
(cond
((not (constant-expression? val))
(log 'not-constant gensym op)
;; At this point, ctx is operator, test, or value. A
;; value that is non-constant in one context will be
;; non-constant in the others, so it's safe to record
;; that here, and avoid future visits.
(set-operand-copyable?! op #f)
(residualize-lexical op ctx val))
((or (const? val)
(void? val)
(primitive-ref? val))
;; Always propagate simple values that cannot lead to
;; code bloat.
(log 'copy-simple gensym val)
;; It could be this constant is the result of folding.
;; If that is the case, cache it. This helps loop
;; unrolling get farther.
(if (or (eq? ctx 'value) (eq? ctx 'values))
(begin
(log 'memoize-constant gensym val)
(set-operand-constant-value! op val)))
val)
((= 1 (var-refcount (operand-var op)))
;; Always propagate values referenced only once.
(log 'copy-single gensym val)
val)
;; FIXME: do demand-driven size accounting rather than
;; these heuristics.
((eq? ctx 'operator)
;; A pure expression in the operator position. Inline
;; if it's a lambda that's small enough.
(if (and (lambda? val)
(small-expression? val operator-size-limit))
(begin
(log 'copy-operator gensym val)
val)
(begin
(log 'too-big-for-operator gensym val)
(residualize-lexical op ctx val))))
(else
;; A pure expression, processed for call or for value.
;; Don't inline lambdas, because they will probably won't
;; fold because we don't know the operator.
(if (and (small-expression? val value-size-limit)
(not (tree-il-any lambda? val)))
(begin
(log 'copy-value gensym val)
val)
(begin
(log 'too-big-or-has-lambda gensym val)
(residualize-lexical op ctx val)))))))
(else
;; Visit failed. Either the operand isn't bound, as in
;; lambda formal parameters, or the copy was aborted.
(log 'unbound-or-aborted gensym op)
(residualize-lexical op)))))
(($ <lexical-set> src name gensym exp)
(let ((op (lookup gensym)))
(if (zero? (var-refcount (operand-var op)))
(let ((exp (for-effect exp)))
(if (void? exp)
exp
(make-seq src exp (make-void #f))))
(begin
(set-operand-residualize?! op #t)
(make-lexical-set src name (operand-sym op) (for-value exp))))))
(($ <let> src names gensyms vals body)
(let* ((vars (map lookup-var gensyms))
(new (fresh-gensyms vars))
(ops (make-bound-operands vars new vals
(lambda (exp counter ctx)
(loop exp env counter ctx))))
(env (fold extend-env env gensyms ops))
(body (loop body env counter ctx)))
(cond
((const? body)
(for-tail (list->seq src (append vals (list body)))))
((and (lexical-ref? body)
(memq (lexical-ref-gensym body) new))
(let ((sym (lexical-ref-gensym body))
(pairs (map cons new vals)))
;; (let ((x foo) (y bar) ...) x) => (begin bar ... foo)
(for-tail
(list->seq
src
(append (map cdr (alist-delete sym pairs eq?))
(list (assq-ref pairs sym)))))))
(else
;; Only include bindings for which lexical references
;; have been residualized.
(prune-bindings ops #f body counter ctx
(lambda (names gensyms vals body)
(if (null? names) (error "what!" names))
(make-let src names gensyms vals body)))))))
(($ <letrec> src in-order? names gensyms vals body)
;; Note the difference from the `let' case: here we use letrec*
;; so that the `visit' procedure for the new operands closes over
;; an environment that includes the operands.
(letrec* ((visit (lambda (exp counter ctx)
(loop exp env* counter ctx)))
(vars (map lookup-var gensyms))
(new (fresh-gensyms vars))
(ops (make-bound-operands vars new vals visit))
(env* (fold extend-env env gensyms ops))
(body* (visit body counter ctx)))
(if (and (const? body*) (every constant-expression? vals))
;; We may have folded a loop completely, even though there
;; might be cyclical references between the bound values.
;; Handle this degenerate case specially.
body*
(prune-bindings ops in-order? body* counter ctx
(lambda (names gensyms vals body)
(make-letrec src in-order?
names gensyms vals body))))))
(($ <fix> src names gensyms vals body)
(letrec* ((visit (lambda (exp counter ctx)
(loop exp env* counter ctx)))
(vars (map lookup-var gensyms))
(new (fresh-gensyms vars))
(ops (make-bound-operands vars new vals visit))
(env* (fold extend-env env gensyms ops))
(body* (visit body counter ctx)))
(if (const? body*)
body*
(prune-bindings ops #f body* counter ctx
(lambda (names gensyms vals body)
(make-fix src names gensyms vals body))))))
(($ <let-values> lv-src producer consumer)
;; Peval the producer, then try to inline the consumer into
;; the producer. If that succeeds, peval again. Otherwise
;; reconstruct the let-values, pevaling the consumer.
(let ((producer (for-values producer)))
(or (match consumer
(($ <lambda-case> src req #f #f #f () gensyms body #f)
(cond
((inline-values producer src req gensyms body)
=> for-tail)
(else #f)))
(_ #f))
(make-let-values lv-src producer (for-tail consumer)))))
(($ <dynwind> src winder pre body post unwinder)
(make-dynwind src (for-value winder) (for-effect pre)
(for-tail body)
(for-effect post) (for-value unwinder)))
(($ <dynlet> src fluids vals body)
(make-dynlet src (map for-value fluids) (map for-value vals)
(for-tail body)))
(($ <dynref> src fluid)
(make-dynref src (for-value fluid)))
(($ <dynset> src fluid exp)
(make-dynset src (for-value fluid) (for-value exp)))
(($ <toplevel-ref> src (? effect-free-primitive? name))
exp)
(($ <toplevel-ref>)
;; todo: open private local bindings.
exp)
(($ <module-ref> src module (? effect-free-primitive? name) #f)
(let ((module (false-if-exception
(resolve-module module #:ensure #f))))
(if (module? module)
(let ((var (module-variable module name)))
(if (eq? var (module-variable the-scm-module name))
(make-primitive-ref src name)
exp))
exp)))
(($ <module-ref>)
exp)
(($ <module-set> src mod name public? exp)
(make-module-set src mod name public? (for-value exp)))
(($ <toplevel-define> src name exp)
(make-toplevel-define src name (for-value exp)))
(($ <toplevel-set> src name exp)
(make-toplevel-set src name (for-value exp)))
(($ <primitive-ref>)
(case ctx
((effect) (make-void #f))
((test) (make-const #f #t))
(else exp)))
(($ <conditional> src condition subsequent alternate)
(let ((condition (for-test condition)))
(if (const? condition)
(if (const-exp condition)
(for-tail subsequent)
(for-tail alternate))
(make-conditional src condition
(for-tail subsequent)
(for-tail alternate)))))
(($ <primcall> src '@call-with-values
(producer
($ <lambda> _ _
(and consumer
;; No optional or kwargs.
($ <lambda-case>
_ req #f rest #f () gensyms body #f)))))
(for-tail (make-let-values src (make-call src producer '())
consumer)))
(($ <primcall> src 'dynamic-wind (w thunk u))
(for-tail
(cond
((not (constant-expression? w))
(cond
((not (constant-expression? u))
(let ((w-sym (gensym "w ")) (u-sym (gensym "u ")))
(record-new-temporary! 'w w-sym 2)
(record-new-temporary! 'u u-sym 2)
(make-let src '(w u) (list w-sym u-sym) (list w u)
(make-dynwind
src
(make-lexical-ref #f 'w w-sym)
(make-call #f (make-lexical-ref #f 'w w-sym) '())
(make-call #f thunk '())
(make-call #f (make-lexical-ref #f 'u u-sym) '())
(make-lexical-ref #f 'u u-sym)))))
(else
(let ((w-sym (gensym "w ")))
(record-new-temporary! 'w w-sym 2)
(make-let src '(w) (list w-sym) (list w)
(make-dynwind
src
(make-lexical-ref #f 'w w-sym)
(make-call #f (make-lexical-ref #f 'w w-sym) '())
(make-call #f thunk '())
(make-call #f u '())
u))))))
((not (constant-expression? u))
(let ((u-sym (gensym "u ")))
(record-new-temporary! 'u u-sym 2)
(make-let src '(u) (list u-sym) (list u)
(make-dynwind
src
w
(make-call #f w '())
(make-call #f thunk '())
(make-call #f (make-lexical-ref #f 'u u-sym) '())
(make-lexical-ref #f 'u u-sym)))))
(else
(make-dynwind src w (make-call #f w '()) (make-call #f thunk '())
(make-call #f u '()) u)))))
(($ <primcall> src 'values exps)
(cond
((null? exps)
(if (eq? ctx 'effect)
(make-void #f)
exp))
(else
(let ((vals (map for-value exps)))
(if (and (case ctx
((value test effect) #t)
(else (null? (cdr vals))))
(every singly-valued-expression? vals))
(for-tail (list->seq src (append (cdr vals) (list (car vals)))))
(make-primcall src 'values vals))))))
(($ <primcall> src (? constructor-primitive? name) args)
(cond
((and (memq ctx '(effect test))
(match (cons name args)
((or ('cons _ _)
('list . _)
('vector . _)
('make-prompt-tag)
('make-prompt-tag ($ <const> _ (? string?))))
#t)
(_ #f)))
;; Some expressions can be folded without visiting the
;; arguments for value.
(let ((res (if (eq? ctx 'effect)
(make-void #f)
(make-const #f #t))))
(for-tail (list->seq src (append args (list res))))))
(else
(match (cons name (map for-value args))
(('cons x ($ <const> _ (? (cut eq? <> '()))))
(make-primcall src 'list (list x)))
(('cons x ($ <primcall> _ 'list elts))
(make-primcall src 'list (cons x elts)))
((name . args)
(make-primcall src name args))))))
(($ <primcall> src (? accessor-primitive? name) args)
(match (cons name (map for-value args))
;; FIXME: these for-tail recursions could take place outside
;; an effort counter.
(('car ($ <primcall> src 'cons (head tail)))
(for-tail (make-seq src tail head)))
(('cdr ($ <primcall> src 'cons (head tail)))
(for-tail (make-seq src head tail)))
(('car ($ <primcall> src 'list (head . tail)))
(for-tail (list->seq src (append tail (list head)))))
(('cdr ($ <primcall> src 'list (head . tail)))
(for-tail (make-seq src head (make-primcall #f 'list tail))))
(('car ($ <const> src (head . tail)))
(for-tail (make-const src head)))
(('cdr ($ <const> src (head . tail)))
(for-tail (make-const src tail)))
(((or 'memq 'memv) k ($ <const> _ (elts ...)))
;; FIXME: factor
(case ctx
((effect)
(for-tail
(make-seq src k (make-void #f))))
((test)
(cond
((const? k)
;; A shortcut. The `else' case would handle it, but
;; this way is faster.
(let ((member (case name ((memq) memq) ((memv) memv))))
(make-const #f (and (member (const-exp k) elts) #t))))
((null? elts)
(for-tail
(make-seq src k (make-const #f #f))))
(else
(let ((t (gensym "t "))
(eq (if (eq? name 'memq) 'eq? 'eqv?)))
(record-new-temporary! 't t (length elts))
(for-tail
(make-let
src (list 't) (list t) (list k)
(let lp ((elts elts))
(define test
(make-primcall #f eq
(list (make-lexical-ref #f 't t)
(make-const #f (car elts)))))
(if (null? (cdr elts))
test
(make-conditional src test
(make-const #f #t)
(lp (cdr elts)))))))))))
(else
(cond
((const? k)
(let ((member (case name ((memq) memq) ((memv) memv))))
(make-const #f (member (const-exp k) elts))))
((null? elts)
(for-tail (make-seq src k (make-const #f #f))))
(else
(make-primcall src name (list k (make-const #f elts))))))))
((name . args)
(fold-constants src name args ctx))))
(($ <primcall> src (? equality-primitive? name) (a b))
(let ((val-a (for-value a))
(val-b (for-value b)))
(log 'equality-primitive name val-a val-b)
(cond ((and (lexical-ref? val-a) (lexical-ref? val-b)
(eq? (lexical-ref-gensym val-a)
(lexical-ref-gensym val-b)))
(for-tail (make-const #f #t)))
(else
(fold-constants src name (list val-a val-b) ctx)))))
(($ <primcall> src (? effect-free-primitive? name) args)
(fold-constants src name (map for-value args) ctx))
(($ <primcall> src name args)
(make-primcall src name (map for-value args)))
(($ <call> src orig-proc orig-args)
;; todo: augment the global env with specialized functions
(let ((proc (visit orig-proc 'operator)))
(match proc
(($ <primitive-ref> _ name)
(for-tail (make-primcall src name orig-args)))
(($ <lambda> _ _
($ <lambda-case> _ req opt #f #f inits gensyms body #f))
;; Simple case: no rest, no keyword arguments.
;; todo: handle the more complex cases
(let* ((nargs (length orig-args))
(nreq (length req))
(nopt (if opt (length opt) 0))
(key (source-expression proc)))
(cond
((or (< nargs nreq) (> nargs (+ nreq nopt)))
;; An error, or effecting arguments.
(make-call src (for-call orig-proc) (map for-value orig-args)))
((or (and=> (find-counter key counter) counter-recursive?)
(lambda? orig-proc))
;; A recursive call, or a lambda in the operator
;; position of the source expression. Process again in
;; tail context.
;;
;; In the recursive case, mark intervening counters as
;; recursive, so we can handle a toplevel counter that
;; recurses mutually with some other procedure.
;; Otherwise, the next time we see the other procedure,
;; the effort limit would be clamped to 100.
;;
(let ((found (find-counter key counter)))
(if (and found (counter-recursive? found))
(let lp ((counter counter))
(if (not (eq? counter found))
(begin
(set-counter-recursive?! counter #t)
(lp (counter-prev counter)))))))
(log 'inline-recurse key)
(loop (make-let src (append req (or opt '()))
gensyms
(append orig-args
(drop inits (- nargs nreq)))
body)
env counter ctx))
(else
;; An integration at the top-level, the first
;; recursion of a recursive procedure, or a nested
;; integration of a procedure that hasn't been seen
;; yet.
(log 'inline-begin exp)
(let/ec k
(define (abort)
(log 'inline-abort exp)
(k (make-call src (for-call orig-proc)
(map for-value orig-args))))
(define new-counter
(cond
;; These first two cases will transfer effort
;; from the current counter into the new
;; counter.
((find-counter key counter)
=> (lambda (prev)
(make-recursive-counter recursive-effort-limit
operand-size-limit
prev counter)))
(counter
(make-nested-counter abort key counter))
;; This case opens a new account, effectively
;; printing money. It should only do so once
;; for each call site in the source program.
(else
(make-top-counter effort-limit operand-size-limit
abort key))))
(define result
(loop (make-let src (append req (or opt '()))
gensyms
(append orig-args
(drop inits (- nargs nreq)))
body)
env new-counter ctx))
(if counter
;; The nested inlining attempt succeeded.
;; Deposit the unspent effort and size back
;; into the current counter.
(transfer! new-counter counter))
(log 'inline-end result exp)
result)))))
(_
(make-call src (for-call orig-proc) (map for-value orig-args))))))
(($ <lambda> src meta body)
(case ctx
((effect) (make-void #f))
((test) (make-const #f #t))
((operator) exp)
(else (record-source-expression!
exp
(make-lambda src meta (for-values body))))))
(($ <lambda-case> src req opt rest kw inits gensyms body alt)
(define (lift-applied-lambda body gensyms)
(and (not opt) rest (not kw)
(match body
(($ <primcall> _ '@apply
(($ <lambda> _ _ lcase)
($ <lexical-ref> _ _ sym)
...))
(and (equal? sym gensyms)
(not (lambda-case-alternate lcase))
lcase))
(_ #f))))
(let* ((vars (map lookup-var gensyms))
(new (fresh-gensyms vars))
(env (fold extend-env env gensyms
(make-unbound-operands vars new)))
(new-sym (lambda (old)
(operand-sym (cdr (vhash-assq old env)))))
(body (loop body env counter ctx)))
(or
;; (lambda args (apply (lambda ...) args)) => (lambda ...)
(lift-applied-lambda body new)
(make-lambda-case src req opt rest
(match kw
((aok? (kw name old) ...)
(cons aok? (map list kw name (map new-sym old))))
(_ #f))
(map (cut loop <> env counter 'value) inits)
new
body
(and alt (for-tail alt))))))
(($ <seq> src head tail)
(let ((head (for-effect head))
(tail (for-tail tail)))
(if (void? head)
tail
(make-seq src
(if (and (seq? head)
(void? (seq-tail head)))
(seq-head head)
head)
tail))))
(($ <prompt> src tag body handler)
(define (singly-used-definition x)
(cond
((and (lexical-ref? x)
;; Only fetch definitions with single uses.
(= (lexical-refcount (lexical-ref-gensym x)) 1)
(lookup (lexical-ref-gensym x)))
=> (lambda (x)
(singly-used-definition (visit-operand x counter 'value 10 10))))
(else x)))
(match (singly-used-definition tag)
(($ <primcall> _ 'make-prompt-tag (or () ((? constant-expression?))))
;; There is no way that an <abort> could know the tag
;; for this <prompt>, so we can elide the <prompt>
;; entirely.
(for-tail body))
(_
(make-prompt src (for-value tag) (for-tail body)
(for-value handler)))))
(($ <abort> src tag args tail)
(make-abort src (for-value tag) (map for-value args)
(for-value tail))))))
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