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More precise dead-after-use? for loop variables

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* module/language/cps/dfg.scm (dead-after-use?):
  (dead-after-branch?): A symbol defined in the header block of a loop
  is still within the same loop.
This commit is contained in:
Andy Wingo 2013-10-12 16:36:28 +02:00
parent b8da548fba
commit 649f6043de
1 changed files with 6 additions and 4 deletions
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10
module/language/cps/dfg.scm
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@ -721,8 +721,9 @@
;; other ways for it to be dead, but this is an approximation.
;; A better check would be if all successors post-dominate all
;; uses.
(and (eqv? (lookup-loop-header use-k blocks)
(lookup-loop-header def blocks))
(and (let ((loop (lookup-loop-header use-k blocks)))
(or (eqv? def loop)
(eqv? (lookup-loop-header def blocks) loop)))
(and-map (cut dominates? <> use-k blocks) uses)))))))
;; A continuation is a "branch" if all of its predecessors are $kif
@ -753,8 +754,9 @@
(($ $use-map sym def uses)
;; As in dead-after-use?, we don't kill the variable if it was
;; defined outside the current loop.
(and (eqv? (lookup-loop-header branch blocks)
(lookup-loop-header def blocks))
(and (let ((loop (lookup-loop-header branch blocks)))
(or (eqv? def loop)
(eqv? (lookup-loop-header def blocks) loop)))
(and-map
(lambda (use-k)
;; A symbol is dead after a branch if at least one of the