diff --git a/basis/compiler/cfg/liveness/ssa/ssa.factor b/basis/compiler/cfg/liveness/ssa/ssa.factor
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+++ b/basis/compiler/cfg/liveness/ssa/ssa.factor
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+! Copyright (C) 2009 Slava Pestov.
+! See http://factorcode.org/license.txt for BSD license.
+USING: kernel namespaces deques accessors sets sequences assocs fry
+hashtables dlists compiler.cfg.def-use compiler.cfg.instructions
+compiler.cfg.rpo compiler.cfg.liveness compiler.cfg.utilities ;
+IN: compiler.cfg.liveness.ssa
+
+! TODO: merge with compiler.cfg.liveness
+
+! Assoc mapping basic blocks to sequences of sets of vregs; each sequence
+! is in correspondence with a predecessor
+SYMBOL: phi-live-ins
+
+: phi-live-in ( predecessor basic-block -- set ) phi-live-ins get at at ;
+
+SYMBOL: work-list
+
+: add-to-work-list ( basic-blocks -- )
+    work-list get '[ _ push-front ] each ;
+
+: compute-live-in ( basic-block -- live-in )
+    [ live-out ] keep instructions>> transfer-liveness ;
+
+: compute-phi-live-in ( basic-block -- phi-live-in )
+    H{ } clone [
+        '[ inputs>> [ swap _ conjoin-at ] assoc-each ] each-phi
+    ] keep ;
+
+: update-live-in ( basic-block -- changed? )
+    [ [ compute-live-in ] keep live-ins get maybe-set-at ]
+    [ [ compute-phi-live-in ] keep phi-live-ins get maybe-set-at ]
+    bi or ;
+
+: compute-live-out ( basic-block -- live-out )
+    [ successors>> [ live-in ] map ]
+    [ dup successors>> [ phi-live-in ] with map ] bi
+    append assoc-combine ;
+
+: update-live-out ( basic-block -- changed? )
+    [ compute-live-out ] keep
+    live-outs get maybe-set-at ;
+
+: liveness-step ( basic-block -- )
+    dup update-live-out [
+        dup update-live-in
+        [ predecessors>> add-to-work-list ] [ drop ] if
+    ] [ drop ] if ;
+
+: compute-ssa-live-sets ( cfg -- cfg' )
+    <hashed-dlist> work-list set
+    H{ } clone live-ins set
+    H{ } clone phi-live-ins set
+    H{ } clone live-outs set
+    dup post-order add-to-work-list
+    work-list get [ liveness-step ] slurp-deque ;
+
+: live-in? ( vreg bb -- ? ) live-in key? ;
+
+: live-out? ( vreg bb -- ? ) live-out key? ;
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