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Conflicts:
	module/language/tree-il/peval.scm
	test-suite/tests/peval.test
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Andy Wingo 2012-04-26 23:08:14 +02:00
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1
module/Makefile.am
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@ -96,6 +96,7 @@ SCHEME_LANG_SOURCES = \
TREE_IL_LANG_SOURCES = \
language/tree-il/primitives.scm \
language/tree-il/peval.scm \
language/tree-il/effects.scm \
language/tree-il/fix-letrec.scm \
language/tree-il/optimize.scm \
language/tree-il/canonicalize.scm \

329
module/language/tree-il/effects.scm Normal file
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@ -0,0 +1,329 @@
;;; Effects analysis on Tree-IL
;; 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 effects)
#:use-module (language tree-il)
#:use-module (language tree-il primitives)
#:use-module (ice-9 match)
#:export (make-effects-analyzer
&mutable-lexical
&toplevel
&fluid
&definite-bailout
&possible-bailout
&zero-values
&allocation
&mutable-data
&type-check
&all-effects
effects-commute?
exclude-effects
effect-free?
constant?
depends-on-effects?
causes-effects?))
;;;
;;; Hey, it's some effects analysis! If you invoke
;;; `make-effects-analyzer', you get a procedure that computes the set
;;; of effects that an expression depends on and causes. This
;;; information is useful when writing algorithms that move code around,
;;; while preserving the semantics of an input program.
;;;
;;; The effects set is represented by a bitfield, as a fixnum. The set
;;; of possible effects is modelled rather coarsely. For example, a
;;; toplevel reference to FOO is modelled as depending on the &toplevel
;;; effect, and causing a &type-check effect. If any intervening code
;;; sets any toplevel variable, that will block motion of FOO.
;;;
;;; For each effect, two bits are reserved: one to indicate that an
;;; expression depends on the effect, and the other to indicate that an
;;; expression causes the effect.
;;;
(define-syntax define-effects
(lambda (x)
(syntax-case x ()
((_ all name ...)
(with-syntax (((n ...) (iota (length #'(name ...)))))
#'(begin
(define name (ash 1 (* n 2)))
...
(define all (logior name ...))))))))
;; Here we define the effects, indicating the meaning of the effect.
;;
;; Effects that are described in a "depends on" sense can also be used
;; in the "causes" sense.
;;
;; Effects that are described as causing an effect are not usually used
;; in a "depends-on" sense. Although the "depends-on" sense is used
;; when checking for the existence of the "causes" effect, the effects
;; analyzer will not associate the "depends-on" sense of these effects
;; with any expression.
;;
(define-effects &all-effects
;; Indicates that an expression depends on the value of a mutable
;; lexical variable.
&mutable-lexical
;; Indicates that an expression depends on the value of a toplevel
;; variable.
&toplevel
;; Indicates that an expression depends on the value of a fluid
;; variable.
&fluid
;; Indicates that an expression definitely causes a non-local,
;; non-resumable exit -- a bailout. Only used in the "changes" sense.
&definite-bailout
;; Indicates that an expression may cause a bailout.
&possible-bailout
;; Indicates than an expression may return zero values -- a "causes"
;; effect.
&zero-values
;; Indicates that an expression may return a fresh object -- a
;; "causes" effect.
&allocation
;; Indicates that an expression depends on the value of a mutable data
;; structure.
&mutable-data
;; Indicates that an expression may cause a type check. A type check,
;; for the purposes of this analysis, is the possibility of throwing
;; an exception the first time an expression is evaluated. If the
;; expression did not cause an exception to be thrown, users can
;; assume that evaluating the expression again will not cause an
;; exception to be thrown.
;;
;; For example, (+ x y) might throw if X or Y are not numbers. But if
;; it doesn't throw, it should be safe to elide a dominated, common
;; subexpression (+ x y).
&type-check)
(define &no-effects 0)
;; Definite bailout is an oddball effect. Since it indicates that an
;; expression definitely causes bailout, it's not in the set of effects
;; of a call to an unknown procedure. At the same time, it's also
;; special in that a definite bailout in a subexpression doesn't always
;; cause an outer expression to include &definite-bailout in its
;; effects. For that reason we have to treat it specially.
;;
(define &all-effects-but-bailout
(logand &all-effects (lognot &definite-bailout)))
(define (cause effect)
(ash effect 1))
(define (&depends-on a)
(logand a &all-effects))
(define (&causes a)
(logand a (cause &all-effects)))
(define (exclude-effects effects exclude)
(logand effects (lognot (cause exclude))))
(define (effect-free? effects)
(zero? (&causes effects)))
(define (constant? effects)
(zero? effects))
(define (depends-on-effects? x effects)
(not (zero? (logand (&depends-on x) effects))))
(define (causes-effects? x effects)
(not (zero? (logand (&causes x) (cause effects)))))
(define (effects-commute? a b)
(and (not (causes-effects? a (&depends-on b)))
(not (causes-effects? b (&depends-on a)))))
(define (make-effects-analyzer assigned-lexical?)
"Returns a procedure of type EXP -> EFFECTS that analyzes the effects
of an expression."
(define compute-effects
(let ((cache (make-hash-table)))
(lambda (exp)
(or (hashq-ref cache exp)
(let ((effects (visit exp)))
(hashq-set! cache exp effects)
effects)))))
(define (accumulate-effects exps)
(let lp ((exps exps) (out &no-effects))
(if (null? exps)
out
(lp (cdr exps) (logior out (compute-effects (car exps)))))))
(define (visit exp)
(match exp
(($ <const>)
&no-effects)
(($ <void>)
&no-effects)
(($ <lexical-ref> _ _ gensym)
(if (assigned-lexical? gensym)
&mutable-lexical
&no-effects))
(($ <lexical-set> _ name gensym exp)
(logior (cause &mutable-lexical)
(compute-effects exp)))
(($ <let> _ names gensyms vals body)
(logior (if (or-map assigned-lexical? gensyms)
(cause &allocation)
&no-effects)
(accumulate-effects vals)
(compute-effects body)))
(($ <letrec> _ in-order? names gensyms vals body)
(logior (if (or-map assigned-lexical? gensyms)
(cause &allocation)
&no-effects)
(accumulate-effects vals)
(compute-effects body)))
(($ <fix> _ names gensyms vals body)
(logior (if (or-map assigned-lexical? gensyms)
(cause &allocation)
&no-effects)
(accumulate-effects vals)
(compute-effects body)))
(($ <let-values> _ producer consumer)
(logior (compute-effects producer)
(compute-effects consumer)
(cause &type-check)))
(($ <dynwind> _ winder pre body post unwinder)
(logior (compute-effects winder)
(compute-effects pre)
(compute-effects body)
(compute-effects post)
(compute-effects unwinder)))
(($ <dynlet> _ fluids vals body)
(logior (accumulate-effects fluids)
(accumulate-effects vals)
(cause &type-check)
(cause &fluid)
(compute-effects body)))
(($ <dynref> _ fluid)
(logior (compute-effects fluid)
(cause &type-check)
&fluid))
(($ <dynset> _ fluid exp)
(logior (compute-effects fluid)
(compute-effects exp)
(cause &type-check)
(cause &fluid)))
(($ <toplevel-ref>)
(logior &toplevel
(cause &type-check)))
(($ <module-ref>)
(logior &toplevel
(cause &type-check)))
(($ <module-set> _ mod name public? exp)
(logior (cause &toplevel)
(cause &type-check)
(compute-effects exp)))
(($ <toplevel-define> _ name exp)
(logior (cause &toplevel)
(compute-effects exp)))
(($ <toplevel-set> _ name exp)
(logior (cause &toplevel)
(compute-effects exp)))
(($ <primitive-ref>)
&no-effects)
(($ <conditional> _ test consequent alternate)
(let ((tfx (compute-effects test))
(cfx (compute-effects consequent))
(afx (compute-effects alternate)))
(if (causes-effects? (logior tfx (logand afx cfx))
&definite-bailout)
(logior tfx cfx afx)
(exclude-effects (logior tfx cfx afx)
&definite-bailout))))
;; Zero values.
(($ <primcall> _ 'values ())
(cause &zero-values))
;; Effect-free primitives.
(($ <primcall> _ (and name (? effect+exception-free-primitive?)) args)
(logior (accumulate-effects args)
(if (constructor-primitive? name)
(cause &allocation)
&no-effects)))
(($ <primcall> _ (and name (? effect-free-primitive?)) args)
(logior (accumulate-effects args)
(cause &type-check)
(if (constructor-primitive? name)
(cause &allocation)
(if (accessor-primitive? name)
&mutable-data
&no-effects))))
;; Lambda applications might throw wrong-number-of-args.
(($ <call> _ ($ <lambda> _ _ body) args)
(logior (compute-effects body)
(accumulate-effects args)
(cause &type-check)))
;; Bailout primitives.
(($ <primcall> _ (? bailout-primitive? name) args)
(logior (accumulate-effects args)
(cause &definite-bailout)
(cause &possible-bailout)))
;; A call to an unknown procedure can do anything.
(($ <primcall> _ name args)
(logior &all-effects-but-bailout
(cause &all-effects-but-bailout)))
(($ <call> _ proc args)
(logior &all-effects-but-bailout
(cause &all-effects-but-bailout)))
(($ <lambda> _ meta body)
&no-effects)
(($ <lambda-case> _ req opt rest kw inits gensyms body alt)
(logior (exclude-effects (accumulate-effects inits)
&definite-bailout)
(if (or-map assigned-lexical? gensyms)
(cause &allocation)
&no-effects)
(compute-effects body)
(if alt (compute-effects alt) &no-effects)))
(($ <seq> _ head tail)
(logior
;; Returning zero values to a for-effect continuation is
;; not observable.
(exclude-effects (compute-effects head)
(cause &zero-values))
(compute-effects tail)))
(($ <prompt> _ tag body handler)
(logior (compute-effects tag)
(compute-effects body)
(compute-effects handler)))
(($ <abort> _ tag args tail)
(logior &all-effects-but-bailout
(cause &all-effects-but-bailout)))))
compute-effects)

79
module/language/tree-il/peval.scm
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@ -19,6 +19,7 @@
(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)
@ -298,12 +299,13 @@
(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.
;; 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 #t) #f #f)))
(%make-operand var sym visit source 0 #f
(and source (not (var-set? var))) #f #f)))
(define (make-bound-operands vars syms sources visit)
(map (lambda (x y z) (make-operand x y z visit)) vars syms sources))
@ -555,52 +557,15 @@ top-level bindings from ENV and return the resulting expression."
(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).
(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))))
(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
@ -940,14 +905,20 @@ top-level bindings from ENV and return the resulting expression."
((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)))))
(match (for-test condition)
(($ <const> _ val)
(if val
(for-tail subsequent)
(for-tail alternate)))
;; Swap the arms of (if (not FOO) A B), to simplify.
(($ <primcall> _ 'not (c))
(make-conditional src c
(for-tail alternate)
(for-tail subsequent)))
(c
(make-conditional src c
(for-tail subsequent)
(for-tail alternate)))))
(($ <primcall> src '@call-with-values
(producer
($ <lambda> _ _

12
test-suite/tests/peval.test
View file

@ -760,15 +760,15 @@
;; This test checks that the `start' binding is indeed residualized.
;; See the `referenced?' procedure in peval's `prune-bindings'.
(let ((pos 0))
(set! pos 1) ;; Cause references to `pos' to residualize.
(let ((here (let ((start pos)) (lambda () start))))
(set! pos 1) ;; Cause references to `pos' to residualize.
(here)))
(let (pos) (_) ((const 0))
(seq
(set! (lexical pos _) (const 1))
(let (here) (_) (_)
(call (lexical here _))))))
(let (here) (_) (_)
(seq
(set! (lexical pos _) (const 1))
(call (lexical here _))))))
(pass-if-peval
;; FIXME: should this one residualize the binding?
(letrec ((a a))