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Replace conservatively-dominates? with a precise dominator lookup

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* module/language/cps/dfg.scm (dominates?): Use the dominator tree
  instead of the scope tree.
This commit is contained in:
Andy Wingo 2013-10-11 14:10:19 +02:00
parent 3aee6cfdd7
commit 238ef4cf44
1 changed files with 13 additions and 13 deletions
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26
module/language/cps/dfg.scm
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@ -486,15 +486,15 @@
uses))))))
;; Does k1 dominate k2?
;;
;; Note that this is a conservative predicate: a false return value does
;; not indicate that k1 _doesn't_ dominate k2. The reason for this is
;; that we are using the scope tree as an approximation of the dominator
;; relationship. See
;; http://mlton.org/pipermail/mlton/2003-January/023054.html for a
;; deeper discussion.
(define (conservatively-dominates? k1 k2 blocks)
(continuation-scope-contains? k1 k2 blocks))
(define (dominates? k1 k2 blocks)
(match (lookup-block k1 blocks)
(($ $block _ _ _ _ k1-idom k1-dom-level)
(match (lookup-block k2 blocks)
(($ $block _ _ _ _ k2-idom k2-dom-level)
(cond
((> k1-dom-level k2-dom-level) #f)
((< k1-dom-level k2-dom-level) (dominates? k1 k2-idom blocks))
((= k1-dom-level k2-dom-level) (eqv? k1 k2))))))))
(define (dead-after-def? sym dfg)
(match dfg
@ -512,7 +512,7 @@
;; are other ways for it to be dead, but this is an
;; approximation. A better check would be if the successor
;; post-dominates all uses.
(and-map (cut conservatively-dominates? <> use-k blocks)
(and-map (cut dominates? <> use-k blocks)
uses))))))
;; A continuation is a "branch" if all of its predecessors are $kif
@ -546,10 +546,10 @@
;; A symbol is dead after a branch if at least one of the
;; other branches dominates a use of the symbol, and all
;; other uses of the symbol dominate the test.
(if (or-map (cut conservatively-dominates? <> use-k blocks)
(if (or-map (cut dominates? <> use-k blocks)
other-branches)
(not (conservatively-dominates? branch use-k blocks))
(conservatively-dominates? use-k branch blocks)))
(not (dominates? branch use-k blocks))
(dominates? use-k branch blocks)))
uses))))))
(define (lookup-bound-syms k dfg)