;;; Tree-IL partial evaluator
-;; Copyright (C) 2011 Free Software Foundation, Inc.
+;; 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
(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)
(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)
+ (($ <application> _
+ ($ <primitive-ref> _ (? singly-valued-primitive?))) #t)
+ (($ <application> _ ($ <primitive-ref> _ '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-application (tree-il-src x)
+ (make-primitive-ref #f '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 <operand>
(%make-operand var sym visit source visit-count residualize?
- copyable? residual-value constant-value)
+ copyable? residual-value constant-value alias-value)
operand?
(var operand-var)
(sym operand-sym)
(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!))
+ (residual-value operand-residual-value %set-operand-residual-value!)
+ (constant-value operand-constant-value set-operand-constant-value!)
+ (alias-value operand-alias-value set-operand-alias-value!))
-(define* (make-operand var sym #:optional source visit)
- ;; Bound operands are considered copyable until we prove otherwise.
- (%make-operand var sym visit source 0 #f (and source #t) #f #f))
+(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 #f
+ (and source (not (var-set? var))) #f #f
+ (and (not (var-set? var)) alias))))
-(define (make-bound-operands vars syms sources visit)
- (map (lambda (x y z) (make-operand x y z visit)) vars syms sources))
+(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
+ (($ <application> src ($ <primitive-ref> _ '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
(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))
+ (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)
;;
(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* (residualize-lexical op #:optional ctx val)
(log 'residualize op)
(set-operand-residualize?! op #t)
- (if (eq? ctx 'value)
+ (if (memq ctx '(value values))
(set-operand-residual-value! op val))
(make-lexical-ref #f (var-name (operand-var op)) (operand-sym op)))
- (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 (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-application src (make-primitive-ref src 'values)
+ values))))
+ (define (residualize-call)
+ (make-application src (make-primitive-ref #f 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))
(and tail
(make-sequence src (append head (list tail)))))))))))
- (define (make-values src values)
- (match values
- ((single) single) ; 1 value
- ((_ ...) ; 0, or 2 or more values
- (make-application src (make-primitive-ref src 'values)
- values))))
+ (define compute-effects
+ (make-effects-analyzer assigned-lexical?))
(define (constant-expression? x)
- ;; Return true if X is constant---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 _ body alternate)
- (and (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)))
- (($ <application> _ ($ <primitive-ref> _ name) args)
- (and (effect-free-primitive? name)
- (not (constructor-primitive? name))
- (not (accessor-primitive? name))
- (types-check? name args)
- (every loop args)))
- (($ <application> _ ($ <lambda> _ _ body) args)
- (and (loop body) (every loop args)))
- (($ <sequence> _ exps)
- (every loop exps))
- (($ <let> _ _ _ vals body)
- (and (every loop vals) (loop body)))
- (($ <letrec> _ _ _ _ vals body)
- (and (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))))
+ ;; 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
(let loop ((exp exp)
(env vlist-null) ; vhash of gensym -> <operand>
(counter #f) ; inlined call stack
- (ctx 'value)) ; effect, value, test, operator, or call
+ (ctx 'values)) ; effect, value, values, test, operator, or call
(define (lookup var)
(cond
((vhash-assq var env) => cdr)
(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))
((eq? ctx 'effect)
(log 'lexical-for-effect gensym)
(make-void #f))
+ ((operand-alias-value op)
+ ;; This is an unassigned operand that simply aliases some
+ ;; other operand. Recurse to avoid residualizing the leaf
+ ;; binding.
+ => for-tail)
((eq? ctx 'call)
;; Don't propagate copies if we are residualizing a call.
(log 'residualize-lexical-call gensym op)
(let ((val (operand-constant-value op)))
(log 'memoized-constant gensym val)
(for-tail val)))
- ((visit-operand op counter ctx recursive-effort-limit operand-size-limit)
+ ((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.
;; It could be this constant is the result of folding.
;; If that is the case, cache it. This helps loop
;; unrolling get farther.
- (if (eq? ctx 'value)
+ (if (or (eq? ctx 'value) (eq? ctx 'values))
(begin
(log 'memoize-constant gensym val)
(set-operand-constant-value! op val)))
(set-operand-residualize?! op #t)
(make-lexical-set src name (operand-sym op) (for-value exp))))))
(($ <let> src names gensyms vals body)
+ (define (compute-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)))
+ (or (operand-alias-value op)
+ exp))))
+ (_ #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))))
+ (loop exp env counter ctx))
+ (map compute-alias vals)))
(env (fold extend-env env gensyms ops))
(body (loop body env counter ctx)))
(cond
(($ <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.
+ ;; 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))
(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))
+ (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)
;; 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-value producer)))
+ (let ((producer (for-values producer)))
(or (match consumer
(($ <lambda-case> src req #f #f #f () gensyms body #f)
(cond
(_ #f))
(make-let-values lv-src producer (for-tail consumer)))))
(($ <dynwind> src winder body unwinder)
- (make-dynwind src (for-value winder) (for-tail body)
- (for-value unwinder)))
+ (let ((pre (for-value winder))
+ (body (for-tail body))
+ (post (for-value unwinder)))
+ (cond
+ ((not (constant-expression? pre))
+ (cond
+ ((not (constant-expression? post))
+ (let ((pre-sym (gensym "pre-")) (post-sym (gensym "post-")))
+ (record-new-temporary! 'pre pre-sym 1)
+ (record-new-temporary! 'post post-sym 1)
+ (make-let src '(pre post) (list pre-sym post-sym) (list pre post)
+ (make-dynwind src
+ (make-lexical-ref #f 'pre pre-sym)
+ body
+ (make-lexical-ref #f 'post post-sym)))))
+ (else
+ (let ((pre-sym (gensym "pre-")))
+ (record-new-temporary! 'pre pre-sym 1)
+ (make-let src '(pre) (list pre-sym) (list pre)
+ (make-dynwind src
+ (make-lexical-ref #f 'pre pre-sym)
+ body
+ post))))))
+ ((not (constant-expression? post))
+ (let ((post-sym (gensym "post-")))
+ (record-new-temporary! 'post post-sym 1)
+ (make-let src '(post) (list post-sym) (list post)
+ (make-dynwind src
+ pre
+ body
+ (make-lexical-ref #f 'post post-sym)))))
+ (else
+ (make-dynwind src pre body post)))))
(($ <dynlet> src fluids vals body)
(make-dynlet src (map for-value fluids) (map for-value vals)
(for-tail body)))
((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)))))
+ (define (call-with-failure-thunk exp proc)
+ (match exp
+ (($ <application> _ _ ()) (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-application #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
+ ($ <application> _ ($ <primitive-ref> _ 'not) (pred))
+ subsequent alternate)
+ (simplify-conditional
+ (make-conditional src pred alternate subsequent)))
+ ;; 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))))))
(($ <application> src
($ <primitive-ref> _ '@call-with-values)
(producer
_ req #f rest #f () gensyms body #f)))))
(for-tail (make-let-values src (make-application src producer '())
consumer)))
-
+ (($ <application> src ($ <primitive-ref> _ '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 (make-sequence src (append (cdr vals) (list (car vals)))))
+ (make-application src (make-primitive-ref #f 'values) vals))))))
(($ <application> src orig-proc orig-args)
;; todo: augment the global env with specialized functions
(let ((proc (visit orig-proc 'operator)))
(match (cons name (map for-value orig-args))
(('cons head tail)
(match tail
- (($ <const> src ())
+ (($ <const> src (? (cut eq? <> '())))
(make-application src (make-primitive-ref #f 'list)
(list head)))
(($ <application> src ($ <primitive-ref> _ 'list) elts)
(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-sequence src (list 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-sequence src (list 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-application
+ #f (make-primitive-ref #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-sequence src (list k (make-const #f #f)))))
+ (else
+ (make-application src proc (list k (make-const #f elts))))))))
((_ . args)
- (make-application src proc args))))
+ (or (fold-constants src name args ctx)
+ (make-application src proc args)))))
(($ <primitive-ref> _ (? effect-free-primitive? name))
(let ((args (map for-value orig-args)))
- (if (every const? args) ; only simple constants
- (let-values (((success? values)
- (apply-primitive name (map const-exp args))))
- (log 'fold success? values exp)
- (if success?
- (case ctx
- ((effect) (make-void #f))
- ((test)
- ;; Values truncation: only take the first
- ;; value.
- (if (pair? values)
- (make-const #f (car values))
- (make-values src '())))
- (else
- (make-values src (map (cut make-const src <>)
- values))))
- (make-application src proc args)))
- (cond
- ((and (eq? ctx 'effect) (types-check? name args))
- (make-void #f))
- (else
- (make-application src proc args))))))
+ (or (fold-constants src name args ctx)
+ (make-application src proc args))))
(($ <lambda> _ _
($ <lambda-case> _ req opt #f #f inits gensyms body #f))
;; Simple case: no rest, no keyword arguments.
((operator) exp)
(else (record-source-expression!
exp
- (make-lambda src meta (for-tail body))))))
+ (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
+ (($ <application> _
+ ($ <primitive-ref> _ '@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))))))
- (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
- (loop body env counter ctx)
- (and alt (for-tail alt)))))
+ (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))))))
(($ <sequence> src exps)
(let lp ((exps exps) (effects '()))
(match exps
HCoop / bpt / guile.git / blobdiff