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;;; Effects analysis on Tree-IL
;; Copyright (C) 2011, 2012, 2013, 2021 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
&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.
;;;
;;; Since we have more bits in a fixnum on 64-bit systems, we can be
;;; more precise without losing efficiency. On a 32-bit system, some of
;;; the more precise effects map to fewer bits.
;;;
(define-syntax define-effects
(lambda (x)
(syntax-case x ()
((_ all name ...)
(with-syntax (((n ...) (iota (length #'(name ...)))))
#'(begin
(define-syntax name (identifier-syntax (ash 1 (* n 2))))
...
(define-syntax all (identifier-syntax (logior name ...)))))))))
(define-syntax compile-time-cond
(lambda (x)
(syntax-case x (else)
((_ (else body ...))
#'(begin body ...))
((_ (exp body ...) clause ...)
(if (eval (syntax->datum #'exp) (current-module))
#'(begin body ...)
#'(compile-time-cond clause ...))))))
;; 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.
;;
(compile-time-cond
((>= (logcount most-positive-fixnum) 60)
(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 the car of a
;; pair.
&car
;; Indicates that an expression depends on the value of the cdr of a
;; pair.
&cdr
;; Indicates that an expression depends on the value of a vector
;; field. We cannot be more precise, as vectors may alias other
;; vectors.
&vector
;; Indicates that an expression depends on the value of a variable
;; cell.
&variable
;; Indicates that an expression depends on the value of a particular
;; struct field.
&struct-0 &struct-1 &struct-2 &struct-3 &struct-4 &struct-5 &struct-6+
;; Indicates that an expression depends on the contents of a string.
&string
;; Indicates that an expression depends on the contents of a
;; bytevector. We cannot be more precise, as bytevectors may alias
;; other bytevectors.
&bytevector
;; 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)
;; Indicates that an expression depends on the contents of an unknown
;; struct field.
(define-syntax &struct
(identifier-syntax
(logior &struct-1 &struct-2 &struct-3 &struct-4 &struct-5 &struct-6+))))
(else
;; For systems with smaller fixnums, be less precise regarding struct
;; fields.
(define-effects &all-effects
&mutable-lexical
&toplevel
&fluid
&definite-bailout
&possible-bailout
&zero-values
&allocation
&car
&cdr
&vector
&variable
&struct
&string
&bytevector
&type-check)
(define-syntax &struct-0 (identifier-syntax &struct))
(define-syntax &struct-1 (identifier-syntax &struct))
(define-syntax &struct-2 (identifier-syntax &struct))
(define-syntax &struct-3 (identifier-syntax &struct))
(define-syntax &struct-4 (identifier-syntax &struct))
(define-syntax &struct-5 (identifier-syntax &struct))
(define-syntax &struct-6+ (identifier-syntax &struct))))
(define-syntax &no-effects (identifier-syntax 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-syntax &all-effects-but-bailout
(identifier-syntax
(logand &all-effects (lognot &definite-bailout))))
(define-inlinable (cause effect)
(ash effect 1))
(define-inlinable (&depends-on a)
(logand a &all-effects))
(define-inlinable (&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-inlinable (depends-on-effects? x effects)
(not (zero? (logand (&depends-on x) effects))))
(define-inlinable (causes-effects? x effects)
(not (zero? (logand (&causes x) (cause effects)))))
(define-inlinable (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."
(let ((cache (make-hash-table)))
(define* (compute-effects exp #:optional (lookup (lambda (x) #f)))
(define (compute-effects 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)))
(($ <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> _ (or 'values 'eq? 'eqv? 'equal?) args)
(accumulate-effects args))
(($ <primcall> _ (or 'not 'pair? 'null? 'list? 'symbol?
'vector? 'struct? 'string? 'number?
'char?)
(arg))
(compute-effects arg))
;; Primitives that allocate memory.
(($ <primcall> _ 'cons (x y))
(logior (compute-effects x) (compute-effects y)
&allocation))
(($ <primcall> _ (or 'list 'vector) args)
(logior (accumulate-effects args) &allocation))
(($ <primcall> _ 'make-prompt-tag ())
&allocation)
(($ <primcall> _ 'make-prompt-tag (arg))
(logior (compute-effects arg) &allocation))
(($ <primcall> _ 'fluid-ref (fluid))
(logior (compute-effects fluid)
(cause &type-check)
&fluid))
(($ <primcall> _ 'fluid-set! (fluid exp))
(logior (compute-effects fluid)
(compute-effects exp)
(cause &type-check)
(cause &fluid)))
(($ <primcall> _ 'push-fluid (fluid val))
(logior (compute-effects fluid)
(compute-effects val)
(cause &type-check)
(cause &fluid)))
(($ <primcall> _ 'pop-fluid ())
(logior (cause &fluid)))
(($ <primcall> _ 'push-dynamic-state (state))
(logior (compute-effects state)
(cause &type-check)
(cause &fluid)))
(($ <primcall> _ 'pop-dynamic-state ())
(logior (cause &fluid)))
(($ <primcall> _ 'car (x))
(logior (compute-effects x)
(cause &type-check)
&car))
(($ <primcall> _ 'set-car! (x y))
(logior (compute-effects x)
(compute-effects y)
(cause &type-check)
(cause &car)))
(($ <primcall> _ 'cdr (x))
(logior (compute-effects x)
(cause &type-check)
&cdr))
(($ <primcall> _ 'set-cdr! (x y))
(logior (compute-effects x)
(compute-effects y)
(cause &type-check)
(cause &cdr)))
(($ <primcall> _ (or 'memq 'memv) (x y))
(logior (compute-effects x)
(compute-effects y)
(cause &type-check)
&car &cdr))
(($ <primcall> _ 'vector-ref (v n))
(logior (compute-effects v)
(compute-effects n)
(cause &type-check)
&vector))
(($ <primcall> _ 'vector-set! (v n x))
(logior (compute-effects v)
(compute-effects n)
(compute-effects x)
(cause &type-check)
(cause &vector)))
(($ <primcall> _ 'variable-ref (v))
(logior (compute-effects v)
(cause &type-check)
&variable))
(($ <primcall> _ 'variable-set! (v x))
(logior (compute-effects v)
(compute-effects x)
(cause &type-check)
(cause &variable)))
(($ <primcall> _ '%variable-ref (v))
(logior (compute-effects v)
(cause &type-check) ;; For the unbound check.
&variable))
(($ <primcall> _ '%variable-set! (v x))
(logior (compute-effects v)
(compute-effects x)
(cause &variable)))
(($ <primcall> _ 'struct-ref (s n))
(logior (compute-effects s)
(compute-effects n)
(cause &type-check)
(match n
(($ <const> _ 0) &struct-0)
(($ <const> _ 1) &struct-1)
(($ <const> _ 2) &struct-2)
(($ <const> _ 3) &struct-3)
(($ <const> _ 4) &struct-4)
(($ <const> _ 5) &struct-5)
(($ <const> _ _) &struct-6+)
(_ &struct))))
(($ <primcall> _ 'struct-set! (s n x))
(logior (compute-effects s)
(compute-effects n)
(compute-effects x)
(cause &type-check)
(match n
(($ <const> _ 0) (cause &struct-0))
(($ <const> _ 1) (cause &struct-1))
(($ <const> _ 2) (cause &struct-2))
(($ <const> _ 3) (cause &struct-3))
(($ <const> _ 4) (cause &struct-4))
(($ <const> _ 5) (cause &struct-5))
(($ <const> _ _) (cause &struct-6+))
(_ (cause &struct)))))
(($ <primcall> _ 'string-ref (s n))
(logior (compute-effects s)
(compute-effects n)
(cause &type-check)
&string))
(($ <primcall> _ 'string-set! (s n c))
(logior (compute-effects s)
(compute-effects n)
(compute-effects c)
(cause &type-check)
(cause &string)))
(($ <primcall> _
(or 'bytevector-u8-ref 'bytevector-s8-ref
'bytevector-u16-ref 'bytevector-u16-native-ref
'bytevector-s16-ref 'bytevector-s16-native-ref
'bytevector-u32-ref 'bytevector-u32-native-ref
'bytevector-s32-ref 'bytevector-s32-native-ref
'bytevector-u64-ref 'bytevector-u64-native-ref
'bytevector-s64-ref 'bytevector-s64-native-ref
'bytevector-ieee-single-ref 'bytevector-ieee-single-native-ref
'bytevector-ieee-double-ref 'bytevector-ieee-double-native-ref)
(bv n))
(logior (compute-effects bv)
(compute-effects n)
(cause &type-check)
&bytevector))
(($ <primcall> _
(or 'bytevector-u8-set! 'bytevector-s8-set!
'bytevector-u16-set! 'bytevector-u16-native-set!
'bytevector-s16-set! 'bytevector-s16-native-set!
'bytevector-u32-set! 'bytevector-u32-native-set!
'bytevector-s32-set! 'bytevector-s32-native-set!
'bytevector-u64-set! 'bytevector-u64-native-set!
'bytevector-s64-set! 'bytevector-s64-native-set!
'bytevector-ieee-single-set! 'bytevector-ieee-single-native-set!
'bytevector-ieee-double-set! 'bytevector-ieee-double-native-set!)
(bv n x))
(logior (compute-effects bv)
(compute-effects n)
(compute-effects x)
(cause &type-check)
(cause &bytevector)))
;; Primitives that are normally effect-free, but which might
;; cause type checks or allocate memory. Nota bene,
;; primitives that access mutable memory should be given their
;; own inline cases above!
(($ <primcall> _ (and name (? effect-free-primitive?)) args)
(logior (accumulate-effects args)
(cause &type-check)
(if (constructor-primitive? name)
(cause &allocation)
&no-effects)))
;; Lambda applications might throw wrong-number-of-args.
(($ <call> _ ($ <lambda> _ _ body) args)
(logior (accumulate-effects args)
(match body
(($ <lambda-case> _ req #f #f #f () syms body #f)
(logior (compute-effects body)
(if (= (length req) (length args))
0
(cause &type-check))))
(($ <lambda-case>)
(logior (compute-effects body)
(cause &type-check)))
(#f
;; Calling a case-lambda with no clauses
;; definitely causes bailout.
(logior (cause &definite-bailout)
(cause &possible-bailout))))))
;; Bailout primitives.
(($ <primcall> _ (? bailout-primitive? name) args)
(logior (accumulate-effects args)
(cause &definite-bailout)
(cause &possible-bailout)))
(($ <call> _
(and proc
($ <module-ref> _ mod name public?)
(? (lambda (_)
(false-if-exception
(procedure-property
(module-ref (if public?
(resolve-interface mod)
(resolve-module mod))
name)
'definite-bailout?)))))
args)
(logior (compute-effects proc)
(accumulate-effects args)
(cause &definite-bailout)
(cause &possible-bailout)))
;; A call to a lexically bound procedure, perhaps labels
;; allocated.
(($ <call> _ (and proc ($ <lexical-ref> _ _ sym)) args)
(cond
((lookup sym)
=> (lambda (proc)
(compute-effects (make-call #f proc args))))
(else
(logior &all-effects-but-bailout
(cause &all-effects-but-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> _ escape-only? tag body handler)
(logior (compute-effects tag)
(compute-effects (if escape-only?
body
(make-call #f body '())))
;; Calls handler with probably wrong argument count,
;; but that will just add a &type-check effect.
(compute-effects (make-call #f handler '()))))
(($ <abort> _ tag args tail)
(logior &all-effects-but-bailout
(cause &all-effects-but-bailout)))))
(compute-effects exp))
compute-effects))