factor/library/compiler/optimizer.factor

! Copyright (C) 2004, 2005 Slava Pestov.
! See http://factor.sf.net/license.txt for BSD license.
IN: compiler-frontend
USING: inference kernel kernel-internals lists namespaces
sequences vectors words words ;

! The optimizer transforms dataflow IR to dataflow IR. Currently
! it 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. Also, #label nodes are inlined if
! their children do not make a recursive call to the label.

: scan-literal ( node -- )
    #! If the node represents a literal push, add the literal to
    #! the list being constructed.
    "scan-literal" [ drop ] apply-dataflow ;

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

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

: scan-branches ( branches -- )
    #! Collect all literals from all branches.
    [ node-param get ] bind [ [ scan-literal ] each ] each ;

: mentions-literal? ( literal list -- ? )
    #! Does the given list of result objects refer to this
    #! literal?
    [ value= ] some-with? ;

: consumes-literal? ( literal node -- ? )
    #! Does the dataflow node consume the literal?
    [
        dup node-consume-d get mentions-literal? swap
        dup node-consume-r get mentions-literal? nip or
    ] bind ;

: produces-literal? ( literal node -- ? )
    #! Does the dataflow node produce the literal?
    [
        dup node-produce-d get mentions-literal? swap
        dup node-produce-r get mentions-literal? nip or
    ] bind ;

: (can-kill?) ( literal node -- ? )
    #! Return false if the literal appears as input to this
    #! node, and this node is not a stack operation.
    2dup consumes-literal? >r produces-literal? r> or not ;

: can-kill? ( literal dataflow -- ? )
    #! Return false if the literal appears in any node in the
    #! list.
    [ dupd "can-kill" [ (can-kill?) ] apply-dataflow ] 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 ;

SYMBOL: branch-returns

: can-kill-branches? ( literal node -- ? )
    #! Check if the literal appears in either branch. This
    #! assumes that the last element of each branch is a #values
    #! node.
    2dup consumes-literal? [
        2drop f
    ] [
        [ node-param get ] bind
        [
            dup [
                peek [ node-consume-d get >vector ] bind
            ] map
            unify-stacks >list
            branch-returns set
            [ dupd can-kill? ] all? nip
        ] with-scope
    ] ifte ;

: kill-node ( literals node -- )
    swap [ over (can-kill?) ] all? [ , ] [ drop ] ifte ;

: (kill-nodes) ( literals dataflow -- )
    #! Append live nodes to currently constructing list.
    [ "kill-node" [ nip , ] apply-dataflow ] each-with ;

: kill-nodes ( literals dataflow -- dataflow )
    #! Remove literals and construct a list.
    [ (kill-nodes) ] make-list ;

: optimize ( dataflow -- dataflow )
    #! Remove redundant literals from the IR. The original IR
    #! is destructively modified.
    dup kill-set swap kill-nodes ;

: kill-branches ( literals node -- )
    [
        node-param [ [ dupd kill-nodes ] map nip ] change
    ] extend , ;

#push [ [ node-param get ] bind , ] "scan-literal" set-word-prop
#push [ consumes-literal? not ] "can-kill" set-word-prop
#push [ kill-node ] "kill-node" set-word-prop

#label [
    [ node-param get ] bind (scan-literals)
] "scan-literal" set-word-prop

#label [
    [ node-param get ] bind can-kill?
] "can-kill" set-word-prop

#call-label [
    [ node-param get ] bind =
] "calls-label" set-word-prop

: calls-label? ( label list -- ? )
    [ "calls-label" [ 2drop f ] apply-dataflow ] some-with? ;

#label [
    [ node-param get ] bind calls-label?
] "calls-label" set-word-prop

#simple-label [
    [ node-param get ] bind calls-label?
] "calls-label" set-word-prop

: branches-call-label? ( label list -- ? )
    [ calls-label? ] some-with? ;

\ ifte [
    [ node-param get ] bind branches-call-label?
] "calls-label" set-word-prop

\ dispatch [
    [ node-param get ] bind branches-call-label?
] "calls-label" set-word-prop

: optimize-label ( -- op )
    #! Does the label node contain calls to itself?
    node-label get node-param get calls-label?
    #label #simple-label ? ;

#label [ ( literals node -- )
    [
        optimize-label node-op set
        node-param [ kill-nodes ] change
    ] extend ,
] "kill-node" set-word-prop

#values [
    dupd consumes-literal? [
        branch-returns get mentions-literal?
    ] [
        drop t
    ] ifte
] "can-kill" set-word-prop

\ ifte [ scan-branches ] "scan-literal" set-word-prop
\ ifte [ can-kill-branches? ] "can-kill" set-word-prop
\ ifte [ kill-branches ] "kill-node" set-word-prop

\ dispatch [ scan-branches ] "scan-literal" set-word-prop
\ dispatch [ can-kill-branches? ] "can-kill" set-word-prop
\ dispatch [ kill-branches ] "kill-node" set-word-prop

! Don't care about inputs to recursive combinator calls
#call-label [ 2drop t ] "can-kill" set-word-prop

\ drop [ 2drop t ] "can-kill" set-word-prop
\ drop [ kill-node ] "kill-node" set-word-prop
\ dup [ 2drop t ] "can-kill" set-word-prop
\ dup [ kill-node ] "kill-node" set-word-prop
\ swap [ 2drop t ] "can-kill" set-word-prop
\ swap [ kill-node ] "kill-node" set-word-prop

: kill-mask ( killing inputs -- mask )
    [ over [ over value= ] some? >boolean nip ] map nip ;

: reduce-stack-op ( literals node map -- )
    #! If certain values passing through a stack op are being
    #! killed, the stack op can be reduced, in extreme cases
    #! to a no-op.
    -rot [
        [ node-consume-d get ] bind kill-mask swap assoc
    ] keep
    over [ [ node-op set ] extend , ] [ 2drop ] ifte ;

\ over [ 2drop t ] "can-kill" set-word-prop
\ over [
    [
        [[ [ f f ] over ]]
        [[ [ f t ] dup  ]]
    ] reduce-stack-op
] "kill-node" set-word-prop

\ pick [ 2drop t ] "can-kill" set-word-prop
\ pick [
    [
        [[ [ f f f ] pick ]]
        [[ [ f f t ] over ]]
        [[ [ f t f ] over ]]
        [[ [ f t t ] dup  ]]
    ] reduce-stack-op
] "kill-node" set-word-prop

\ >r [ 2drop t ] "can-kill" set-word-prop
\ >r [ kill-node ] "kill-node" set-word-prop
\ r> [ 2drop t ] "can-kill" set-word-prop
\ r> [ kill-node ] "kill-node" set-word-prop