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Thread flow analysis through CSE pass

* module/language/cps/cse.scm (<analysis>): New data type, grouping
  available expression analysis, predecessor map, etc.
  (eliminate-common-subexpressions-in-fun): Instead of having a static
  analysis, thread it through the CSE pass so that we can update the CFG
  as we go.
This commit is contained in:
Andy Wingo 2020-05-28 16:47:17 +02:00
parent 6fb0635358
commit 3c4d4acbd4

View file

@ -25,6 +25,7 @@
(define-module (language cps cse) (define-module (language cps cse)
#:use-module (ice-9 match) #:use-module (ice-9 match)
#:use-module (srfi srfi-1) #:use-module (srfi srfi-1)
#:use-module (srfi srfi-9)
#:use-module (srfi srfi-11) #:use-module (srfi srfi-11)
#:use-module (language cps) #:use-module (language cps)
#:use-module (language cps utils) #:use-module (language cps utils)
@ -137,210 +138,224 @@ false. It could be that both true and false proofs are available."
(intset kfun) (intset kfun)
(intmap-add empty-intmap kfun empty-intset))) (intmap-add empty-intmap kfun empty-intset)))
(define-record-type <analysis>
(make-analysis effects clobbers preds avail truthy-labels)
analysis?
(effects analysis-effects)
(clobbers analysis-clobbers)
(preds analysis-preds)
(avail analysis-avail)
(truthy-labels analysis-truthy-labels))
(define (eliminate-common-subexpressions-in-fun kfun conts out) (define (eliminate-common-subexpressions-in-fun kfun conts out)
(let* ((effects (synthesize-definition-effects (compute-effects conts))) (define equiv-set (make-hash-table))
(define (true-idx idx) (ash idx 1))
(define (false-idx idx) (1+ (ash idx 1)))
(define (subst-var substs var)
(intmap-ref substs var (lambda (var) var)))
(define (subst-vars substs vars)
(let lp ((vars vars))
(match vars
(() '())
((var . vars) (cons (subst-var substs var) (lp vars))))))
(define (compute-term-key term)
(match term
(($ $continue k src exp)
(match exp
(($ $const val) (cons 'const val))
(($ $prim name) (cons 'prim name))
(($ $fun body) #f)
(($ $rec names syms funs) #f)
(($ $const-fun label) #f)
(($ $code label) (cons 'code label))
(($ $call proc args) #f)
(($ $callk k proc args) #f)
(($ $primcall name param args) (cons* name param args))
(($ $values args) #f)))
(($ $branch kf kt src op param args) (cons* op param args))
(($ $prompt) #f)
(($ $throw) #f)))
(define (add-substs label defs out substs analysis)
(match analysis
(($ <analysis> effects clobbers preds avail truthy-labels)
(match (trivial-intset (intmap-ref preds label))
(#f substs)
(pred
(match (intmap-ref out pred)
(($ $kargs _ _ ($ $continue _ _ ($ $values vals)))
;; FIXME: Eliminate predecessor entirely, retargetting its
;; predecessors.
(fold (lambda (def var substs)
(intmap-add substs def var))
substs defs vals))
(($ $kargs _ _ term)
(match (compute-term-key term)
(#f #f)
(term-key
(let ((fx (intmap-ref effects pred)))
;; Add residualized definition to the equivalence set.
;; Note that expressions that allocate a fresh object
;; or change the current fluid environment can't be
;; eliminated by CSE (though DCE might do it if the
;; value proves to be unused, in the allocation case).
(when (and (not (causes-effect? fx &allocation))
(not (effect-clobbers? fx (&read-object &fluid))))
(let ((equiv (hash-ref equiv-set term-key '())))
(hash-set! equiv-set term-key (acons pred defs equiv)))))
;; If the predecessor defines auxiliary definitions, as
;; `cons' does for the results of `car' and `cdr', define
;; those as well.
(add-auxiliary-definitions! pred defs substs term-key)))
substs)
(_
substs)))))))
(define (add-auxiliary-definitions! label defs substs term-key)
(define (add-def! aux-key var)
(let ((equiv (hash-ref equiv-set aux-key '())))
(hash-set! equiv-set aux-key
(acons label (list var) equiv))))
(define-syntax add-definitions
(syntax-rules (<-)
((add-definitions)
#f)
((add-definitions
((def <- op arg ...) (aux <- op* arg* ...) ...)
. clauses)
(match term-key
(('op arg ...)
(match defs
(#f
;; If the successor is a control-flow join, don't
;; pretend to know the values of its defs.
#f)
((def) (add-def! (list 'op* arg* ...) aux) ...)))
(_ (add-definitions . clauses))))
((add-definitions
((op arg ...) (aux <- op* arg* ...) ...)
. clauses)
(match term-key
(('op arg ...)
(add-def! (list 'op* arg* ...) aux) ...)
(_ (add-definitions . clauses))))))
(add-definitions
((scm-set! p s i x) (x <- scm-ref p s i))
((scm-set!/tag p s x) (x <- scm-ref/tag p s))
((scm-set!/immediate p s x) (x <- scm-ref/immediate p s))
((word-set! p s i x) (x <- word-ref p s i))
((word-set!/immediate p s x) (x <- word-ref/immediate p s))
((pointer-set!/immediate p s x) (x <- pointer-ref/immediate p s))
((u <- scm->f64 #f s) (s <- f64->scm #f u))
((s <- f64->scm #f u) (u <- scm->f64 #f s))
((u <- scm->u64 #f s) (s <- u64->scm #f u))
((s <- u64->scm #f u) (u <- scm->u64 #f s)
(u <- scm->u64/truncate #f s))
((s <- u64->scm/unlikely #f u) (u <- scm->u64 #f s)
(u <- scm->u64/truncate #f s))
((u <- scm->s64 #f s) (s <- s64->scm #f u))
((s <- s64->scm #f u) (u <- scm->s64 #f s))
((s <- s64->scm/unlikely #f u) (u <- scm->s64 #f s))
((u <- untag-fixnum #f s) (s <- s64->scm #f u)
(s <- tag-fixnum #f u))
;; NB: These definitions rely on U having top 2 bits equal to
;; 3rd (sign) bit.
((s <- tag-fixnum #f u) (u <- scm->s64 #f s)
(u <- untag-fixnum #f s))
((s <- u64->s64 #f u) (u <- s64->u64 #f s))
((u <- s64->u64 #f s) (s <- u64->s64 #f u))
((u <- untag-char #f s) (s <- tag-char #f u))
((s <- tag-char #f u) (u <- untag-char #f s))))
(define (rename-uses term substs)
(define (subst-var var)
(intmap-ref substs var (lambda (var) var)))
(define (rename-exp exp)
(rewrite-exp exp
((or ($ $const) ($ $prim) ($ $fun) ($ $rec) ($ $const-fun) ($ $code))
,exp)
(($ $call proc args)
($call (subst-var proc) ,(map subst-var args)))
(($ $callk k proc args)
($callk k (and proc (subst-var proc)) ,(map subst-var args)))
(($ $primcall name param args)
($primcall name param ,(map subst-var args)))
(($ $values args)
($values ,(map subst-var args)))))
(rewrite-term term
(($ $branch kf kt src op param args)
($branch kf kt src op param ,(map subst-var args)))
(($ $continue k src exp)
($continue k src ,(rename-exp exp)))
(($ $prompt k kh src escape? tag)
($prompt k kh src escape? (subst-var tag)))
(($ $throw src op param args)
($throw src op param ,(map subst-var args)))))
(define (visit-label label cont out substs analysis)
(define (add cont)
(intmap-add! out label cont))
(match cont
(($ $kargs names vars term)
(let* ((substs (add-substs label vars out substs analysis))
(term (rename-uses term substs)))
(define (residualize)
(add (build-cont ($kargs names vars ,term))))
(define (eliminate k src vals)
(add (build-cont ($kargs names vars
($continue k src ($values vals))))))
(values
(match (compute-term-key term)
(#f (residualize))
(term-key
(match analysis
(($ <analysis> effects clobbers preds avail truthy-labels)
(let ((avail (intmap-ref avail label)))
(let lp ((candidates (hash-ref equiv-set term-key '())))
(match candidates
(()
;; No available expression; residualize.
(residualize))
(((candidate . vars) . candidates)
(cond
((not (intset-ref avail candidate))
;; This expression isn't available here; try
;; the next one.
(lp candidates))
(else
(match term
(($ $continue k src)
;; Yay, a match; eliminate the expression.
(eliminate k src vars))
(($ $branch kf kt src)
(let* ((bool (intmap-ref truthy-labels label))
(t (intset-ref bool (true-idx candidate)))
(f (intset-ref bool (false-idx candidate))))
(if (eqv? t f)
;; Can't fold the branch; keep on
;; looking for another candidate.
(lp candidates)
;; Nice, the branch folded.
(eliminate (if t kt kf) src '())))))))))))))))
substs analysis)))
(_ (values (add cont) substs analysis))))
;; Because of the renumber pass, the labels are numbered in reverse
;; post-order, so the intmap-fold will visit definitions before
;; uses.
(let* ((substs empty-intmap)
(effects (synthesize-definition-effects (compute-effects conts)))
(clobbers (compute-clobber-map effects)) (clobbers (compute-clobber-map effects))
(succs (compute-successors conts kfun)) (succs (compute-successors conts kfun))
(preds (invert-graph succs)) (preds (invert-graph succs))
(avail (compute-available-expressions succs kfun clobbers)) (avail (compute-available-expressions succs kfun clobbers))
(truthy-labels (compute-truthy-expressions conts kfun)) (truthy-labels (compute-truthy-expressions conts kfun)))
(equiv-set (make-hash-table))) (intmap-fold visit-label conts out substs
(define (true-idx idx) (ash idx 1)) (make-analysis effects clobbers preds avail truthy-labels))))
(define (false-idx idx) (1+ (ash idx 1)))
(define (subst-var var-substs var)
(intmap-ref var-substs var (lambda (var) var)))
(define (subst-vars var-substs vars)
(let lp ((vars vars))
(match vars
(() '())
((var . vars) (cons (subst-var var-substs var) (lp vars))))))
(define (compute-term-key term)
(match term
(($ $continue k src exp)
(match exp
(($ $const val) (cons 'const val))
(($ $prim name) (cons 'prim name))
(($ $fun body) #f)
(($ $rec names syms funs) #f)
(($ $const-fun label) #f)
(($ $code label) (cons 'code label))
(($ $call proc args) #f)
(($ $callk k proc args) #f)
(($ $primcall name param args) (cons* name param args))
(($ $values args) #f)))
(($ $branch kf kt src op param args) (cons* op param args))
(($ $prompt) #f)
(($ $throw) #f)))
(define (add-var-substs label defs out var-substs)
(match (trivial-intset (intmap-ref preds label))
(#f var-substs)
(pred
(match (intmap-ref out pred)
(($ $kargs _ _ ($ $continue _ _ ($ $values vals)))
;; FIXME: Eliminate predecessor entirely, retargetting its
;; predecessors.
(fold (lambda (def var var-substs)
(intmap-add var-substs def var))
var-substs defs vals))
(($ $kargs _ _ term)
(match (compute-term-key term)
(#f #f)
(term-key
(let ((fx (intmap-ref effects pred)))
;; Add residualized definition to the equivalence set.
;; Note that expressions that allocate a fresh object
;; or change the current fluid environment can't be
;; eliminated by CSE (though DCE might do it if the
;; value proves to be unused, in the allocation case).
(when (and (not (causes-effect? fx &allocation))
(not (effect-clobbers? fx (&read-object &fluid))))
(let ((equiv (hash-ref equiv-set term-key '())))
(hash-set! equiv-set term-key (acons pred defs equiv)))))
;; If the predecessor defines auxiliary definitions, as
;; `cons' does for the results of `car' and `cdr', define
;; those as well.
(add-auxiliary-definitions! pred defs var-substs term-key)))
var-substs)
(_
var-substs)))))
(define (add-auxiliary-definitions! label defs var-substs term-key)
(let ((defs (and defs (subst-vars var-substs defs))))
(define (add-def! aux-key var)
(let ((equiv (hash-ref equiv-set aux-key '())))
(hash-set! equiv-set aux-key
(acons label (list var) equiv))))
(define-syntax add-definitions
(syntax-rules (<-)
((add-definitions)
#f)
((add-definitions
((def <- op arg ...) (aux <- op* arg* ...) ...)
. clauses)
(match term-key
(('op arg ...)
(match defs
(#f
;; If the successor is a control-flow join, don't
;; pretend to know the values of its defs.
#f)
((def) (add-def! (list 'op* arg* ...) aux) ...)))
(_ (add-definitions . clauses))))
((add-definitions
((op arg ...) (aux <- op* arg* ...) ...)
. clauses)
(match term-key
(('op arg ...)
(add-def! (list 'op* arg* ...) aux) ...)
(_ (add-definitions . clauses))))))
(add-definitions
((scm-set! p s i x) (x <- scm-ref p s i))
((scm-set!/tag p s x) (x <- scm-ref/tag p s))
((scm-set!/immediate p s x) (x <- scm-ref/immediate p s))
((word-set! p s i x) (x <- word-ref p s i))
((word-set!/immediate p s x) (x <- word-ref/immediate p s))
((pointer-set!/immediate p s x) (x <- pointer-ref/immediate p s))
((u <- scm->f64 #f s) (s <- f64->scm #f u))
((s <- f64->scm #f u) (u <- scm->f64 #f s))
((u <- scm->u64 #f s) (s <- u64->scm #f u))
((s <- u64->scm #f u) (u <- scm->u64 #f s)
(u <- scm->u64/truncate #f s))
((s <- u64->scm/unlikely #f u) (u <- scm->u64 #f s)
(u <- scm->u64/truncate #f s))
((u <- scm->s64 #f s) (s <- s64->scm #f u))
((s <- s64->scm #f u) (u <- scm->s64 #f s))
((s <- s64->scm/unlikely #f u) (u <- scm->s64 #f s))
((u <- untag-fixnum #f s) (s <- s64->scm #f u)
(s <- tag-fixnum #f u))
;; NB: These definitions rely on U having top 2 bits equal to
;; 3rd (sign) bit.
((s <- tag-fixnum #f u) (u <- scm->s64 #f s)
(u <- untag-fixnum #f s))
((s <- u64->s64 #f u) (u <- s64->u64 #f s))
((u <- s64->u64 #f s) (s <- u64->s64 #f u))
((u <- untag-char #f s) (s <- tag-char #f u))
((s <- tag-char #f u) (u <- untag-char #f s)))))
(define (rename-uses term var-substs)
(define (subst-var var)
(intmap-ref var-substs var (lambda (var) var)))
(define (rename-exp exp)
(rewrite-exp exp
((or ($ $const) ($ $prim) ($ $fun) ($ $rec) ($ $const-fun) ($ $code))
,exp)
(($ $call proc args)
($call (subst-var proc) ,(map subst-var args)))
(($ $callk k proc args)
($callk k (and proc (subst-var proc)) ,(map subst-var args)))
(($ $primcall name param args)
($primcall name param ,(map subst-var args)))
(($ $values args)
($values ,(map subst-var args)))))
(rewrite-term term
(($ $branch kf kt src op param args)
($branch kf kt src op param ,(map subst-var args)))
(($ $continue k src exp)
($continue k src ,(rename-exp exp)))
(($ $prompt k kh src escape? tag)
($prompt k kh src escape? (subst-var tag)))
(($ $throw src op param args)
($throw src op param ,(map subst-var args)))))
(define (visit-label label cont out var-substs)
(define (add cont)
(intmap-add! out label cont))
(match cont
(($ $kargs names vars term)
(let* ((var-substs (add-var-substs label vars out var-substs))
(term (rename-uses term var-substs)))
(define (residualize)
(add (build-cont ($kargs names vars ,term))))
(define (eliminate k src vals)
(add (build-cont ($kargs names vars
($continue k src ($values vals))))))
(values
(match (compute-term-key term)
(#f (residualize))
(term-key
(let ((avail (intmap-ref avail label)))
(let lp ((candidates (hash-ref equiv-set term-key '())))
(match candidates
(()
;; No available expression; residualize.
(residualize))
(((candidate . vars) . candidates)
(cond
((not (intset-ref avail candidate))
;; This expression isn't available here; try
;; the next one.
(lp candidates))
(else
(match term
(($ $continue k src)
;; Yay, a match; eliminate the expression.
(eliminate k src vars))
(($ $branch kf kt src)
(let* ((bool (intmap-ref truthy-labels label))
(t (intset-ref bool (true-idx candidate)))
(f (intset-ref bool (false-idx candidate))))
(if (eqv? t f)
;; Can't fold the branch; keep on
;; looking for another candidate.
(lp candidates)
;; Nice, the branch folded.
(eliminate (if t kt kf) src '())))))))))))))
var-substs)))
(_ (values (add cont) var-substs))))
;; Because of the renumber pass, the labels are numbered in reverse
;; post-order, so the intmap-fold will visit definitions before
;; uses.
(intmap-fold visit-label conts out empty-intmap)))
(define (fold-renumbered-functions f conts seed) (define (fold-renumbered-functions f conts seed)
;; Precondition: CONTS has been renumbered, and therefore functions ;; Precondition: CONTS has been renumbered, and therefore functions