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+;;; Tree-IL partial evaluator
+
+;; Copyright (C) 2011-2014, 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
+
+(define-module (language tree-il peval)
+ #:use-module (language tree-il)
+ #:use-module (language tree-il primitives)
+ #:use-module (language tree-il effects)
+ #: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)
+ #:use-module (ice-9 control)
+ #: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 (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) #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)
+ (($ <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)
+ (($ <conditional> _ test consequent alternate)
+ (and (singly-valued-expression? consequent)
+ (singly-valued-expression? alternate)))
+ (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))
+ (($ <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 use-count
+ copyable? residual-value constant-value alias)
+ operand?
+ (var operand-var)
+ (sym operand-sym)
+ (visit %operand-visit)
+ (source operand-source)
+ (visit-count operand-visit-count set-operand-visit-count!)
+ (use-count operand-use-count set-operand-use-count!)
+ (copyable? operand-copyable? set-operand-copyable?!)
+ (residual-value operand-residual-value %set-operand-residual-value!)
+ (constant-value operand-constant-value set-operand-constant-value!)
+ (alias operand-alias set-operand-alias!))
+
+(define* (make-operand var sym #:optional source visit alias)
+ ;; Bind SYM to VAR, with value SOURCE. Unassigned 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 0
+ (and source (not (var-set? var))) #f #f
+ (and (not (var-set? var)) alias))))
+
+(define* (make-bound-operands vars syms sources visit #:optional aliases)
+ (if aliases
+ (map (lambda (name sym source alias)
+ (make-operand name sym source visit alias))
+ vars syms sources aliases)
+ (map (lambda (name sym source)
+ (make-operand name sym source visit #f))
+ 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)
+ ;; If we abort when visiting the value in a
+ ;; fresh context, we won't succeed in any future
+ ;; attempt, so don't try to copy it again.
+ (set-operand-copyable?! op #f)
+ (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 (fresh-temporaries ls)
+ (map (lambda (elt)
+ (let ((new (gensym "tmp ")))
+ (record-new-temporary! 'tmp new 1)
+ new))
+ ls))
+
+ (define (assigned-lexical? sym)
+ (var-set? (lookup-var sym)))
+
+ (define (lexical-refcount sym)
+ (var-refcount (lookup-var sym)))
+
+ (define (with-temporaries src exps refcount can-copy? k)
+ (let* ((pairs (map (match-lambda
+ ((and exp (? can-copy?))
+ (cons #f exp))
+ (exp
+ (let ((sym (gensym "tmp ")))
+ (record-new-temporary! 'tmp sym refcount)
+ (cons sym exp))))
+ exps))
+ (tmps (filter car pairs)))
+ (match tmps
+ (() (k exps))
+ (tmps
+ (make-let src
+ (make-list (length tmps) 'tmp)
+ (map car tmps)
+ (map cdr tmps)
+ (k (map (match-lambda
+ ((#f . val) val)
+ ((sym . _)
+ (make-lexical-ref #f 'tmp sym)))
+ pairs)))))))
+
+ (define (make-begin0 src first second)
+ (make-let-values
+ src
+ first
+ (let ((vals (gensym "vals ")))
+ (record-new-temporary! 'vals vals 1)
+ (make-lambda-case
+ #f
+ '() #f 'vals #f '() (list vals)
+ (make-seq
+ src
+ second
+ (make-primcall #f 'apply
+ (list
+ (make-primitive-ref #f 'values)
+ (make-lexical-ref #f 'vals vals))))
+ #f))))
+
+ ;; 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 (record-operand-use op)
+ (set-operand-use-count! op (1+ (operand-use-count op))))
+
+ (define (unrecord-operand-uses op n)
+ (let ((count (- (operand-use-count op) n)))
+ (when (zero? count)
+ (set-operand-residual-value! op #f))
+ (set-operand-use-count! op count)))
+
+ (define* (residualize-lexical op #:optional ctx val)
+ (log 'residualize op)
+ (record-operand-use op)
+ (if (memq ctx '(value values))
+ (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 ()
+ (case name
+ ((eq? eqv?)
+ ;; Constants will be deduplicated later, but eq?
+ ;; folding can happen now. Anticipate the
+ ;; deduplication by using equal? instead of eq?.
+ ;; Same for eqv?.
+ (apply equal? args))
+ (else
+ (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 src exp nmin nmax consumer)
+ (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>)
+ ($ <lexical-set>) ; FIXME: these set! expressions
+ ($ <toplevel-set>) ; could return zero values in
+ ($ <toplevel-define>) ; the future
+ ($ <module-set>) ;
+ ($ <primcall> src (? singly-valued-primitive?)))
+ (and (<= nmin 1) (or (not nmax) (>= nmax 1))
+ (make-call src (make-lambda #f '() consumer) (list exp))))
+
+ ;; Statically-known number of values.
+ (($ <primcall> src 'values vals)
+ (and (<= nmin (length vals)) (or (not nmax) (>= nmax (length vals)))
+ (make-call src (make-lambda #f '() consumer) vals)))
+
+ ;; 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)))))
+ (($ <seq> src head tail)
+ (let ((tail (loop tail)))
+ (and tail (make-seq src head tail)))))))
+
+ (define compute-effects
+ (make-effects-analyzer assigned-lexical?))
+
+ (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).
+ (constant? (compute-effects x)))
+
+ (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)
+ (not (zero? (operand-use-count 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) ; 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))))
+
+ ;; Find a value referenced a specific number of times. This is a hack
+ ;; that's used for propagating fresh data structures like rest lists and
+ ;; prompt tags. Usually we wouldn't copy consed data, but we can do so in
+ ;; some special cases like `apply' or prompts if we can account
+ ;; for all of its uses.
+ ;;
+ ;; You don't want to use this in general because it introduces a slight
+ ;; nonlinearity by running peval again (though with a small effort and size
+ ;; counter).
+ ;;
+ (define (find-definition x n-aliases)
+ (cond
+ ((lexical-ref? x)
+ (cond
+ ((lookup (lexical-ref-gensym x))
+ => (lambda (op)
+ (if (var-set? (operand-var op))
+ (values #f #f)
+ (let ((y (or (operand-residual-value op)
+ (visit-operand op counter 'value 10 10)
+ (operand-source op))))
+ (cond
+ ((and (lexical-ref? y)
+ (= (lexical-refcount (lexical-ref-gensym x)) 1))
+ ;; X is a simple alias for Y. Recurse, regardless of
+ ;; the number of aliases we were expecting.
+ (find-definition y n-aliases))
+ ((= (lexical-refcount (lexical-ref-gensym x)) n-aliases)
+ ;; We found a definition that is aliased the right
+ ;; number of times. We still recurse in case it is a
+ ;; lexical.
+ (values (find-definition y 1)
+ op))
+ (else
+ ;; We can't account for our aliases.
+ (values #f #f)))))))
+ (else
+ ;; A formal parameter. Can't say anything about that.
+ (values #f #f))))
+ ((= n-aliases 1)
+ ;; Not a lexical: success, but only if we are looking for an
+ ;; unaliased value.
+ (values x #f))
+ (else (values #f #f))))
+
+ (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 lp ((op (lookup gensym)))
+ (cond
+ ((eq? ctx 'effect)
+ (log 'lexical-for-effect gensym)
+ (make-void #f))
+ ((operand-alias op)
+ ;; This is an unassigned operand that simply aliases some
+ ;; other operand. Recurse to avoid residualizing the leaf
+ ;; binding.
+ => lp)
+ ((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
+ (record-operand-use op)
+ (make-lexical-set src name (operand-sym op) (for-value exp))))))
+ (($ <let> src
+ (names ... rest)
+ (gensyms ... rest-sym)
+ (vals ... ($ <primcall> _ 'list rest-args))
+ ($ <primcall> asrc 'apply
+ (proc args ...
+ ($ <lexical-ref> _
+ (? (cut eq? <> rest))
+ (? (lambda (sym)
+ (and (eq? sym rest-sym)
+ (= (lexical-refcount sym) 1))))))))
+ (let* ((tmps (make-list (length rest-args) 'tmp))
+ (tmp-syms (fresh-temporaries tmps)))
+ (for-tail
+ (make-let src
+ (append names tmps)
+ (append gensyms tmp-syms)
+ (append vals rest-args)
+ (make-call
+ asrc
+ proc
+ (append args
+ (map (cut make-lexical-ref #f <> <>)
+ tmps tmp-syms)))))))
+ (($ <let> src names gensyms vals body)
+ (define (lookup-alias exp)
+ ;; It's very common for macros to introduce something like:
+ ;;
+ ;; ((lambda (x y) ...) x-exp y-exp)
+ ;;
+ ;; In that case you might end up trying to inline something like:
+ ;;
+ ;; (let ((x x-exp) (y y-exp)) ...)
+ ;;
+ ;; But if x-exp is itself a lexical-ref that aliases some much
+ ;; larger expression, perhaps it will fail to inline due to
+ ;; size. However we don't want to introduce a useless alias
+ ;; (in this case, x). So if the RHS of a let expression is a
+ ;; lexical-ref, we record that expression. If we end up having
+ ;; to residualize X, then instead we residualize X-EXP, as long
+ ;; as it isn't assigned.
+ ;;
+ (match exp
+ (($ <lexical-ref> _ _ sym)
+ (let ((op (lookup sym)))
+ (and (not (var-set? (operand-var op))) op)))
+ (_ #f)))
+
+ (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))
+ (map lookup-alias vals)))
+ (env (fold extend-env env gensyms ops))
+ (body (loop body env counter ctx)))
+ (match body
+ (($ <const>)
+ (for-tail (list->seq src (append vals (list body)))))
+ (($ <lexical-ref> _ _ (? (lambda (sym) (memq sym new)) sym))
+ (let ((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)))))))
+ ((and ($ <conditional> src*
+ ($ <lexical-ref> _ _ sym) ($ <lexical-ref> _ _ sym) alt)
+ (? (lambda (_)
+ (case ctx
+ ((test effect)
+ (and (equal? (list sym) new)
+ (= (lexical-refcount sym) 2)))
+ (else #f)))))
+ ;; (let ((x EXP)) (if x x ALT)) -> (if EXP #t ALT) in test context
+ (make-conditional src* (visit-operand (car ops) counter 'test)
+ (make-const src* #t) alt))
+ (_
+ ;; 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. Also we don't try
+ ;; to elide aliases, because we can't sensibly reduce something
+ ;; like (letrec ((a b) (b a)) a).
+ (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
+ ((and ($ <lambda-case> src () #f rest #f () (rest-sym) body #f)
+ (? (lambda _ (singly-valued-expression? producer))))
+ (let ((tmp (gensym "tmp ")))
+ (record-new-temporary! 'tmp tmp 1)
+ (for-tail
+ (make-let
+ src (list 'tmp) (list tmp) (list producer)
+ (make-let
+ src (list rest) (list rest-sym)
+ (list
+ (make-primcall #f 'list
+ (list (make-lexical-ref #f 'tmp tmp))))
+ body)))))
+ (($ <lambda-case> src req opt rest #f inits gensyms body #f)
+ (let* ((nmin (length req))
+ (nmax (and (not rest) (+ nmin (if opt (length opt) 0)))))
+ (cond
+ ((inline-values lv-src producer nmin nmax consumer)
+ => for-tail)
+ (else #f))))
+ (_ #f))
+ (make-let-values lv-src producer (for-tail consumer)))))
+ (($ <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)
+ (define (call-with-failure-thunk exp proc)
+ (match exp
+ (($ <call> _ _ ()) (proc exp))
+ (($ <primcall> _ _ ()) (proc exp))
+ (($ <const>) (proc exp))
+ (($ <void>) (proc exp))
+ (($ <lexical-ref>) (proc exp))
+ (_
+ (let ((t (gensym "failure-")))
+ (record-new-temporary! 'failure t 2)
+ (make-let
+ src (list 'failure) (list t)
+ (list
+ (make-lambda
+ #f '()
+ (make-lambda-case #f '() #f #f #f '() '() exp #f)))
+ (proc (make-call #f (make-lexical-ref #f 'failure t)
+ '())))))))
+ (define (simplify-conditional c)
+ (match c
+ ;; Swap the arms of (if (not FOO) A B), to simplify.
+ (($ <conditional> src ($ <primcall> _ 'not (pred))
+ subsequent alternate)
+ (simplify-conditional
+ (make-conditional src pred alternate subsequent)))
+ ;; In the following four cases, we try to expose the test to
+ ;; the conditional. This will let the CPS conversion avoid
+ ;; reifying boolean literals in some cases.
+ (($ <conditional> src ($ <let> src* names vars vals body)
+ subsequent alternate)
+ (make-let src* names vars vals
+ (simplify-conditional
+ (make-conditional src body subsequent alternate))))
+ (($ <conditional> src
+ ($ <letrec> src* in-order? names vars vals body)
+ subsequent alternate)
+ (make-letrec src* in-order? names vars vals
+ (simplify-conditional
+ (make-conditional src body subsequent alternate))))
+ (($ <conditional> src ($ <fix> src* names vars vals body)
+ subsequent alternate)
+ (make-fix src* names vars vals
+ (simplify-conditional
+ (make-conditional src body subsequent alternate))))
+ (($ <conditional> src ($ <seq> src* head tail)
+ subsequent alternate)
+ (make-seq src* head
+ (simplify-conditional
+ (make-conditional src tail subsequent alternate))))
+ ;; Special cases for common tests in the predicates of chains
+ ;; of if expressions.
+ (($ <conditional> src
+ ($ <conditional> src* outer-test inner-test ($ <const> _ #f))
+ inner-subsequent
+ alternate)
+ (let lp ((alternate alternate))
+ (match alternate
+ ;; Lift a common repeated test out of a chain of if
+ ;; expressions.
+ (($ <conditional> _ (? (cut tree-il=? outer-test <>))
+ other-subsequent alternate)
+ (make-conditional
+ src outer-test
+ (simplify-conditional
+ (make-conditional src* inner-test inner-subsequent
+ other-subsequent))
+ alternate))
+ ;; Likewise, but punching through any surrounding
+ ;; failure continuations.
+ (($ <let> let-src (name) (sym) ((and thunk ($ <lambda>))) body)
+ (make-let
+ let-src (list name) (list sym) (list thunk)
+ (lp body)))
+ ;; Otherwise, rotate AND tests to expose a simple
+ ;; condition in the front. Although this may result in
+ ;; lexically binding failure thunks, the thunks will be
+ ;; compiled to labels allocation, so there's no actual
+ ;; code growth.
+ (_
+ (call-with-failure-thunk
+ alternate
+ (lambda (failure)
+ (make-conditional
+ src outer-test
+ (simplify-conditional
+ (make-conditional src* inner-test inner-subsequent failure))
+ failure)))))))
+ (_ c)))
+ (match (for-test condition)
+ (($ <const> _ val)
+ (if val
+ (for-tail subsequent)
+ (for-tail alternate)))
+ (c
+ (simplify-conditional
+ (make-conditional src c (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
+ (with-temporaries
+ src (list w u) 2 constant-expression?
+ (match-lambda
+ ((w u)
+ (make-seq
+ src
+ (make-seq
+ src
+ (make-conditional
+ src
+ ;; fixme: introduce logic to fold thunk?
+ (make-primcall src 'thunk? (list u))
+ (make-call src w '())
+ (make-primcall
+ src 'throw
+ (list
+ (make-const #f 'wrong-type-arg)
+ (make-const #f "dynamic-wind")
+ (make-const #f "Wrong type (expecting thunk): ~S")
+ (make-primcall #f 'list (list u))
+ (make-primcall #f 'list (list u)))))
+ (make-primcall src 'wind (list w u)))
+ (make-begin0 src
+ (make-call src thunk '())
+ (make-seq src
+ (make-primcall src 'unwind '())
+ (make-call src u '())))))))))
+
+ (($ <primcall> src 'with-fluid* (f v thunk))
+ (for-tail
+ (with-temporaries
+ src (list f v thunk) 1 constant-expression?
+ (match-lambda
+ ((f v thunk)
+ (make-seq src
+ (make-primcall src 'push-fluid (list f v))
+ (make-begin0 src
+ (make-call src thunk '())
+ (make-primcall src 'pop-fluid '()))))))))
+
+ (($ <primcall> src 'with-dynamic-state (state thunk))
+ (for-tail
+ (with-temporaries
+ src (list state thunk) 1 constant-expression?
+ (match-lambda
+ ((state thunk)
+ (make-seq src
+ (make-primcall src 'push-dynamic-state (list state))
+ (make-begin0 src
+ (make-call src thunk '())
+ (make-primcall src 'pop-dynamic-state
+ '()))))))))
+
+ (($ <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 'apply (proc args ... tail))
+ (let lp ((tail* (find-definition tail 1)) (speculative? #t))
+ (define (copyable? x)
+ ;; Inlining a result from find-definition effectively copies it,
+ ;; relying on the let-pruning to remove its original binding. We
+ ;; shouldn't copy non-constant expressions.
+ (or (not speculative?) (constant-expression? x)))
+ (match tail*
+ (($ <const> _ (args* ...))
+ (let ((args* (map (cut make-const #f <>) args*)))
+ (for-tail (make-call src proc (append args args*)))))
+ (($ <primcall> _ 'cons
+ ((and head (? copyable?)) (and tail (? copyable?))))
+ (for-tail (make-primcall src 'apply
+ (cons proc
+ (append args (list head tail))))))
+ (($ <primcall> _ 'list
+ (and args* ((? copyable?) ...)))
+ (for-tail (make-call src proc (append args args*))))
+ (tail*
+ (if speculative?
+ (lp (for-value tail) #f)
+ (let ((args (append (map for-value args) (list tail*))))
+ (make-primcall src 'apply
+ (cons (for-value proc) args))))))))
+
+ (($ <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)))
+ (('list)
+ (make-const src '()))
+ (('vector)
+ (make-const src '#()))
+ ((name . args)
+ (make-primcall src name args))))))
+
+ (($ <primcall> src 'thunk? (proc))
+ (case ctx
+ ((effect)
+ (for-tail (make-seq src proc (make-void src))))
+ (else
+ (match (for-value proc)
+ (($ <lambda> _ _ ($ <lambda-case> _ req))
+ (for-tail (make-const src (null? req))))
+ (proc
+ (match (find-definition proc 2)
+ (($ <lambda> _ _ ($ <lambda-case> _ req))
+ (for-tail (make-const src (null? req))))
+ (_
+ (make-primcall src 'thunk? (list proc)))))))))
+
+ (($ <primcall> src 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))))))))
+ (((? equality-primitive?)
+ ($ <lexical-ref> _ _ sym) ($ <lexical-ref> _ _ sym))
+ (for-tail (make-const #f #t)))
+
+ (('logbit? ($ <const> src2
+ (? (lambda (bit)
+ (and (exact-integer? bit)
+ (<= 0 bit (logcount most-positive-fixnum))))
+ bit))
+ val)
+ (for-tail
+ (make-primcall src 'logtest
+ (list (make-const src2 (ash 1 bit)) val))))
+
+ (('logtest a b)
+ (for-tail
+ (make-primcall
+ src
+ 'not
+ (list
+ (make-primcall src 'eq?
+ (list (make-primcall src 'logand (list a b))
+ (make-const src 0)))))))
+
+ (((? effect-free-primitive?) . args)
+ (fold-constants src name args ctx))
+
+ ((name . args)
+ (make-primcall src name args))))
+
+ (($ <call> src orig-proc orig-args)
+ ;; todo: augment the global env with specialized functions
+ (let revisit-proc ((proc (visit orig-proc 'operator)))
+ (match proc
+ (($ <primitive-ref> _ name)
+ (for-tail
+ (expand-primcall (make-primcall src name orig-args))))
+ (($ <lambda> _ _
+ ($ <lambda-case> _ req opt rest #f inits gensyms body #f))
+ ;; Simple case: no keyword arguments.
+ ;; todo: handle the more complex cases
+ (let* ((nargs (length orig-args))
+ (nreq (length req))
+ (opt (or opt '()))
+ (rest (if rest (list rest) '()))
+ (nopt (length opt))
+ (key (source-expression proc)))
+ (define (singly-referenced-lambda? orig-proc)
+ (match orig-proc
+ (($ <lambda>) #t)
+ (($ <lexical-ref> _ _ sym)
+ (and (not (assigned-lexical? sym))
+ (= (lexical-refcount sym) 1)
+ (singly-referenced-lambda?
+ (operand-source (lookup sym)))))
+ (_ #f)))
+ (define (inlined-call)
+ (let ((req-vals (list-head orig-args nreq))
+ (opt-vals (let lp ((args (drop orig-args nreq))
+ (inits inits)
+ (out '()))
+ (match inits
+ (() (reverse out))
+ ((init . inits)
+ (match args
+ (()
+ (lp '() inits (cons init out)))
+ ((arg . args)
+ (lp args inits (cons arg out))))))))
+ (rest-vals (cond
+ ((> nargs (+ nreq nopt))
+ (list (make-primcall
+ #f 'list
+ (drop orig-args (+ nreq nopt)))))
+ ((null? rest) '())
+ (else (list (make-const #f '()))))))
+ (if (>= nargs (+ nreq nopt))
+ (make-let src
+ (append req opt rest)
+ gensyms
+ (append req-vals opt-vals rest-vals)
+ body)
+ ;; The default initializers of optional arguments
+ ;; may refer to earlier arguments, so in the general
+ ;; case we must expand into a series of nested let
+ ;; expressions.
+ ;;
+ ;; In the generated code, the outermost let
+ ;; expression will bind all required arguments, as
+ ;; well as the empty rest argument, if any. Each
+ ;; optional argument will be bound within an inner
+ ;; let.
+ (make-let src
+ (append req rest)
+ (append (list-head gensyms nreq)
+ (last-pair gensyms))
+ (append req-vals rest-vals)
+ (fold-right (lambda (var gensym val body)
+ (make-let src
+ (list var)
+ (list gensym)
+ (list val)
+ body))
+ body
+ opt
+ (list-head (drop gensyms nreq) nopt)
+ opt-vals)))))
+
+ (cond
+ ((or (< nargs nreq) (and (not rest) (> 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?)
+ (singly-referenced-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 (inlined-call) 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 (inlined-call) 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)))))
+ (($ <let> _ _ _ vals _)
+ ;; Attempt to inline `let' in the operator position.
+ ;;
+ ;; We have to re-visit the proc in value mode, since the
+ ;; `let' bindings might have been introduced or renamed,
+ ;; whereas the lambda (if any) in operator position has not
+ ;; been renamed.
+ (if (or (and-map constant-expression? vals)
+ (and-map constant-expression? orig-args))
+ ;; The arguments and the let-bound values commute.
+ (match (for-value orig-proc)
+ (($ <let> lsrc names syms vals body)
+ (log 'inline-let orig-proc)
+ (for-tail
+ (make-let lsrc names syms vals
+ (make-call src body orig-args))))
+ ;; It's possible for a `let' to go away after the
+ ;; visit due to the fact that visiting a procedure in
+ ;; value context will prune unused bindings, whereas
+ ;; visiting in operator mode can't because it doesn't
+ ;; traverse through lambdas. In that case re-visit
+ ;; the procedure.
+ (proc (revisit-proc proc)))
+ (make-call src (for-call orig-proc)
+ (map for-value orig-args))))
+ (_
+ (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 (and body (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> _ _ (and lcase ($ <lambda-case> _ req1)))
+ ($ <lexical-ref> _ _ sym)
+ ...))
+ (and (equal? sym gensyms)
+ (not (lambda-case-alternate lcase))
+ (<= (length req) (length req1))
+ (every (lambda (s)
+ (= (lexical-refcount s) 1))
+ sym)
+ 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 escape-only? tag body handler)
+ (define (make-prompt-tag? x)
+ (match x
+ (($ <primcall> _ 'make-prompt-tag (or () ((? constant-expression?))))
+ #t)
+ (_ #f)))
+
+ (let ((tag (for-value tag))
+ (body (if escape-only? (for-tail body) (for-value body))))
+ (cond
+ ((find-definition tag 1)
+ (lambda (val op)
+ (make-prompt-tag? val))
+ => (lambda (val op)
+ ;; There is no way that an <abort> could know the tag
+ ;; for this <prompt>, so we can elide the <prompt>
+ ;; entirely.
+ (unrecord-operand-uses op 1)
+ (for-tail (if escape-only? body (make-call src body '())))))
+ (else
+ (let ((handler (for-value handler)))
+ (define (escape-only-handler? handler)
+ (match handler
+ (($ <lambda> _ _
+ ($ <lambda-case> _ (_ . _) _ _ _ _ (k . _) body #f))
+ (not (tree-il-any
+ (match-lambda
+ (($ <lexical-ref> _ _ (? (cut eq? <> k))) #t)
+ (_ #f))
+ body)))
+ (else #f)))
+ (if (and (not escape-only?) (escape-only-handler? handler))
+ ;; Prompt transitioning to escape-only; transition body
+ ;; to be an expression.
+ (for-tail
+ (make-prompt src #t tag (make-call #f body '()) handler))
+ (make-prompt src escape-only? tag body handler)))))))
+
+ (($ <abort> src tag args tail)
+ (make-abort src (for-value tag) (map for-value args)
+ (for-value tail))))))