! :folding=indent:collapseFolds=1:

! $Id$
!
! Copyright (C) 2004 Slava Pestov.
! 
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IN: compiler
USE: lists
USE: stack
USE: combinators
USE: namespaces
USE: kernel
USE: inference
USE: words
USE: prettyprint
USE: logic

! The optimizer transforms dataflow IR to dataflow IR. Currently
! it simply removes literals that are eventually dropped, and
! never arise as inputs to any other type of function. Such
! 'dead' literals arise when combinators are inlined and
! quotations are lifted to their call sites.

: scan-literal ( node -- )
    "scan-literal" [ 2drop ] apply-dataflow ;

: scan-literals ( dataflow -- list )
    [ [ scan-literal ] each ] make-list ;

: scan-branches ( branches -- )
    [ [ scan-literal ] each ] each ;

: mentions-literal? ( literal list -- )
    #! Does the given list of result objects refer to this
    #! literal?
    [ dup cons? [ car over = ] [ drop f ] ifte ] some? ;

: (can-kill?) ( literal node -- ? )
    #! Return false if the literal appears as input to this
    #! node, and this node is not a stack operation.
    [
        node-consume-d get mentions-literal? swap
        node-consume-r get mentions-literal? nip or not
    ] bind ;

: can-kill? ( literal dataflow -- ? )
    [ dupd (can-kill?) ] all? nip ;

: kill-set ( dataflow -- list )
    #! Push a list of literals that may be killed in the IR.
    dup scan-literals [ over can-kill? ] subset nip ;

#push [ , ] "scan-literal" set-word-property
#ifte [ scan-branches ] "scan-literal" set-word-property
#generic [ scan-branches ] "scan-literal" set-word-property
#2generic [ scan-branches ] "scan-literal" set-word-property