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Simplify live variable computation for graphs without loops

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* module/language/cps/slot-allocation.scm
  (compute-reverse-control-flow-order): For graphs without back-edges,
  use a simplified computation of reverse control flow order.
This commit is contained in:
Andy Wingo 2017-11-29 19:57:48 +01:00
parent b077e807c0
commit 39520f879a
1 changed files with 29 additions and 11 deletions
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40
module/language/cps/slot-allocation.scm
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@ -23,6 +23,7 @@
;;; Code:
(define-module (language cps slot-allocation)
#:use-module (ice-9 control)
#:use-module (ice-9 match)
#:use-module (srfi srfi-1)
#:use-module (srfi srfi-9)
@ -171,17 +172,34 @@ by a label, respectively."
(define (compute-reverse-control-flow-order preds)
"Return a LABEL->ORDER bijection where ORDER is a contiguous set of
integers starting from 0 and incrementing in sort order."
;; This is more involved than forward control flow because not all
;; live labels are reachable from the tail.
(persistent-intmap
(fold2 (lambda (component order n)
(intset-fold (lambda (label order n)
(values (intmap-add! order label n)
(1+ n)))
component order n))
(reverse (compute-sorted-strongly-connected-components preds))
empty-intmap 0)))
integers starting from 0 and incrementing in sort order. There is a
precondition that labels in PREDS are already renumbered in reverse post
order."
(define (has-back-edge? preds)
(let/ec return
(intmap-fold (lambda (label labels)
(intset-fold (lambda (pred)
(if (<= label pred)
(return #t)
(values)))
labels)
(values))
preds)
#f))
(if (has-back-edge? preds)
;; This is more involved than forward control flow because not all
;; live labels are reachable from the tail.
(persistent-intmap
(fold2 (lambda (component order n)
(intset-fold (lambda (label order n)
(values (intmap-add! order label n)
(1+ n)))
component order n))
(reverse (compute-sorted-strongly-connected-components preds))
empty-intmap 0))
;; Just reverse forward control flow.
(let ((max (intmap-prev preds)))
(intmap-map (lambda (label labels) (- max label)) preds))))
(define* (add-prompt-control-flow-edges conts succs #:key complete?)
"For all prompts in DFG in the range [MIN-LABEL, MIN-LABEL +