diff --git a/basis/compiler/cfg/alias-analysis/alias-analysis.factor b/basis/compiler/cfg/alias-analysis/alias-analysis.factor
index 78e271c1f6..f6834c131d 100644
--- a/basis/compiler/cfg/alias-analysis/alias-analysis.factor
+++ b/basis/compiler/cfg/alias-analysis/alias-analysis.factor
@@ -3,7 +3,7 @@
 USING: kernel math namespaces assocs hashtables sequences arrays
 accessors vectors combinators sets classes compiler.cfg
 compiler.cfg.registers compiler.cfg.instructions
-compiler.cfg.copy-prop compiler.cfg.rpo compiler.cfg.def-use ;
+compiler.cfg.copy-prop compiler.cfg.rpo compiler.cfg.liveness ;
 IN: compiler.cfg.alias-analysis
 
 ! We try to eliminate redundant slot operations using some simple heuristics.
@@ -196,9 +196,6 @@ M: ##set-slot insn-object obj>> resolve ;
 M: ##set-slot-imm insn-object obj>> resolve ;
 M: ##alien-global insn-object drop \ ##alien-global ;
 
-: inputs ( insns -- seq )
-    [ [ ##phi? not ] filter gen-set ] [ kill-set ] bi assoc-diff keys ;
-
 : init-alias-analysis ( insns -- insns' )
     H{ } clone histories set
     H{ } clone vregs>acs set
@@ -210,7 +207,7 @@ M: ##alien-global insn-object drop \ ##alien-global ;
     0 ac-counter set
     next-ac heap-ac set
 
-    dup inputs [ set-heap-ac ] each ;
+    dup local-live-in [ set-heap-ac ] each ;
 
 GENERIC: analyze-aliases* ( insn -- insn' )
 
diff --git a/basis/compiler/cfg/dominance/dominance-tests.factor b/basis/compiler/cfg/dominance/dominance-tests.factor
index 210d5614c2..e884e32d78 100644
--- a/basis/compiler/cfg/dominance/dominance-tests.factor
+++ b/basis/compiler/cfg/dominance/dominance-tests.factor
@@ -6,8 +6,7 @@ compiler.cfg.predecessors ;
 : test-dominance ( -- )
     cfg new 0 get >>entry
     compute-predecessors
-    compute-dominance
-    drop ;
+    compute-dominance ;
 
 ! Example with no back edges
 V{ } 0 test-bb
@@ -74,3 +73,25 @@ V{ } 5 test-bb
 [ ] [ test-dominance ] unit-test
 
 [ t ] [ 0 5 [a,b] [ get dom-parent 0 get eq? ] all? ] unit-test
+
+V{ } 0 test-bb
+V{ } 1 test-bb
+V{ } 2 test-bb
+V{ } 3 test-bb
+V{ } 4 test-bb
+V{ } 5 test-bb
+V{ } 6 test-bb
+
+0 get 1 get 5 get V{ } 2sequence >>successors drop
+1 get 2 get 3 get V{ } 2sequence >>successors drop
+2 get 4 get 1vector >>successors drop
+3 get 4 get 1vector >>successors drop
+4 get 6 get 1vector >>successors drop
+5 get 6 get 1vector >>successors drop
+
+[ ] [ test-dominance ] unit-test
+
+[ t ] [
+    2 get 3 get 2array iterated-dom-frontier
+    4 get 6 get 2array set=
+] unit-test
\ No newline at end of file
diff --git a/basis/compiler/cfg/dominance/dominance.factor b/basis/compiler/cfg/dominance/dominance.factor
index 9c8fc79619..73d9f58eec 100644
--- a/basis/compiler/cfg/dominance/dominance.factor
+++ b/basis/compiler/cfg/dominance/dominance.factor
@@ -1,7 +1,7 @@
 ! Copyright (C) 2009 Slava Pestov.
 ! See http://factorcode.org/license.txt for BSD license.
 USING: accessors assocs combinators sets math fry kernel math.order
-namespaces sequences sorting compiler.cfg.rpo ;
+dlists deques namespaces sequences sorting compiler.cfg.rpo ;
 IN: compiler.cfg.dominance
 
 ! Reference:
@@ -85,8 +85,31 @@ PRIVATE>
 
 PRIVATE>
 
-: compute-dominance ( cfg -- cfg' )
+: compute-dominance ( cfg -- )
     [ compute-dom-parents compute-dom-children ]
     [ compute-dom-frontiers ]
-    [ ]
-    tri ;
+    bi ;
+
+<PRIVATE
+
+SYMBOLS: work-list visited ;
+
+: add-to-work-list ( bb -- )
+    dom-frontier work-list get push-all-front ;
+
+: iterated-dom-frontier-step ( bb -- )
+    dup visited get key? [ drop ] [
+        [ visited get conjoin ]
+        [ add-to-work-list ] bi
+    ] if ;
+
+PRIVATE>
+
+: iterated-dom-frontier ( bbs -- bbs' )
+    [
+        <dlist> work-list set
+        H{ } clone visited set
+        [ add-to-work-list ] each
+        work-list get [ iterated-dom-frontier-step ] slurp-deque
+        visited get keys
+    ] with-scope ;
\ No newline at end of file
diff --git a/basis/compiler/cfg/linear-scan/assignment/assignment.factor b/basis/compiler/cfg/linear-scan/assignment/assignment.factor
index 952feb5919..8e21e7e3fb 100644
--- a/basis/compiler/cfg/linear-scan/assignment/assignment.factor
+++ b/basis/compiler/cfg/linear-scan/assignment/assignment.factor
@@ -6,13 +6,13 @@ cpu.architecture
 compiler.cfg
 compiler.cfg.rpo
 compiler.cfg.def-use
+compiler.cfg.liveness
 compiler.cfg.registers
 compiler.cfg.instructions
 compiler.cfg.linear-scan.mapping
 compiler.cfg.linear-scan.allocation
 compiler.cfg.linear-scan.allocation.state
-compiler.cfg.linear-scan.live-intervals
-compiler.cfg.linear-scan.liveness ;
+compiler.cfg.linear-scan.live-intervals ;
 IN: compiler.cfg.linear-scan.assignment
 
 ! This contains both active and inactive intervals; any interval
diff --git a/basis/compiler/cfg/linear-scan/linear-scan.factor b/basis/compiler/cfg/linear-scan/linear-scan.factor
index 186a773355..b081f2ca6e 100644
--- a/basis/compiler/cfg/linear-scan/linear-scan.factor
+++ b/basis/compiler/cfg/linear-scan/linear-scan.factor
@@ -4,9 +4,9 @@ USING: kernel accessors namespaces make locals
 cpu.architecture
 compiler.cfg
 compiler.cfg.rpo
+compiler.cfg.liveness
 compiler.cfg.instructions
 compiler.cfg.linear-scan.numbering
-compiler.cfg.linear-scan.liveness
 compiler.cfg.linear-scan.live-intervals
 compiler.cfg.linear-scan.allocation
 compiler.cfg.linear-scan.allocation.state
diff --git a/basis/compiler/cfg/linear-scan/live-intervals/live-intervals.factor b/basis/compiler/cfg/linear-scan/live-intervals/live-intervals.factor
index 244f2bc069..8813a4e94e 100644
--- a/basis/compiler/cfg/linear-scan/live-intervals/live-intervals.factor
+++ b/basis/compiler/cfg/linear-scan/live-intervals/live-intervals.factor
@@ -2,7 +2,7 @@
 ! See http://factorcode.org/license.txt for BSD license.
 USING: namespaces kernel assocs accessors sequences math math.order fry
 combinators binary-search compiler.cfg.instructions compiler.cfg.registers
-compiler.cfg.def-use compiler.cfg.linear-scan.liveness compiler.cfg.rpo
+compiler.cfg.def-use compiler.cfg.liveness compiler.cfg.rpo
 compiler.cfg ;
 IN: compiler.cfg.linear-scan.live-intervals
 
diff --git a/basis/compiler/cfg/linear-scan/liveness/liveness.factor b/basis/compiler/cfg/linear-scan/liveness/liveness.factor
deleted file mode 100644
index ac36fca9c7..0000000000
--- a/basis/compiler/cfg/linear-scan/liveness/liveness.factor
+++ /dev/null
@@ -1,17 +0,0 @@
-! Copyright (C) 2009 Slava Pestov.
-! See http://factorcode.org/license.txt for BSD license.
-USING: kernel accessors assocs compiler.cfg.def-use
-compiler.cfg.dataflow-analysis ;
-IN: compiler.cfg.linear-scan.liveness
-
-! See http://en.wikipedia.org/wiki/Liveness_analysis
-
-BACKWARD-ANALYSIS: live
-
-M: live-analysis transfer-set
-    drop instructions>>
-    [ gen-set assoc-union ] keep
-    kill-set assoc-diff ;
-
-M: live-analysis join-sets
-    drop assoc-combine ;
\ No newline at end of file
diff --git a/basis/compiler/cfg/linear-scan/resolve/resolve.factor b/basis/compiler/cfg/linear-scan/resolve/resolve.factor
index 5bab261ea8..56beaa5379 100644
--- a/basis/compiler/cfg/linear-scan/resolve/resolve.factor
+++ b/basis/compiler/cfg/linear-scan/resolve/resolve.factor
@@ -4,11 +4,11 @@ USING: accessors arrays assocs combinators
 combinators.short-circuit fry kernel locals
 make math sequences
 compiler.cfg.rpo
+compiler.cfg.liveness
 compiler.cfg.utilities
 compiler.cfg.instructions
 compiler.cfg.linear-scan.assignment
-compiler.cfg.linear-scan.mapping
-compiler.cfg.linear-scan.liveness ;
+compiler.cfg.linear-scan.mapping ;
 IN: compiler.cfg.linear-scan.resolve
 
 : add-mapping ( from to reg-class -- )
diff --git a/basis/compiler/cfg/liveness/liveness-tests.factor b/basis/compiler/cfg/liveness/liveness-tests.factor
new file mode 100644
index 0000000000..697a1f8a7b
--- /dev/null
+++ b/basis/compiler/cfg/liveness/liveness-tests.factor
@@ -0,0 +1,38 @@
+USING: compiler.cfg.liveness compiler.cfg.debugger
+compiler.cfg.instructions compiler.cfg.predecessors
+compiler.cfg.registers compiler.cfg cpu.architecture
+accessors namespaces sequences kernel tools.test ;
+IN: compiler.cfg.liveness.tests
+
+! Sanity check...
+
+V{
+    T{ ##peek f V int-regs 0 D 0 }
+    T{ ##replace f V int-regs 0 D 0 }
+    T{ ##replace f V int-regs 1 D 1 }
+    T{ ##peek f V int-regs 1 D 1 }
+} 1 test-bb
+
+V{
+    T{ ##replace f V int-regs 2 D 0 }
+} 2 test-bb
+
+V{
+    T{ ##replace f V int-regs 3 D 0 }
+} 3 test-bb
+
+1 get 2 get 3 get V{ } 2sequence >>successors drop
+
+cfg new 1 get >>entry
+compute-predecessors
+compute-live-sets
+
+[
+    H{
+        { V int-regs 1 V int-regs 1 }
+        { V int-regs 2 V int-regs 2 }
+        { V int-regs 3 V int-regs 3 }
+    }
+]
+[ 1 get live-in ]
+unit-test
\ No newline at end of file
diff --git a/basis/compiler/cfg/liveness/liveness.factor b/basis/compiler/cfg/liveness/liveness.factor
new file mode 100644
index 0000000000..c1793842a2
--- /dev/null
+++ b/basis/compiler/cfg/liveness/liveness.factor
@@ -0,0 +1,26 @@
+! Copyright (C) 2009 Slava Pestov.
+! See http://factorcode.org/license.txt for BSD license.
+USING: kernel accessors assocs sequences sets
+compiler.cfg.def-use compiler.cfg.dataflow-analysis
+compiler.cfg.instructions ;
+IN: compiler.cfg.liveness
+
+! See http://en.wikipedia.org/wiki/Liveness_analysis
+! Do not run after SSA construction
+
+BACKWARD-ANALYSIS: live
+
+: transfer-liveness ( live-set instructions -- live-set' )
+    [ clone ] [ <reversed> ] bi* [
+        [ uses-vregs [ over conjoin ] each ]
+        [ defs-vregs [ over delete-at ] each ] bi
+    ] each ;
+
+: local-live-in ( instructions -- live-set )
+    [ ##phi? not ] filter [ H{ } ] dip transfer-liveness keys ;
+
+M: live-analysis transfer-set
+    drop instructions>> transfer-liveness ;
+
+M: live-analysis join-sets
+    drop assoc-combine ;
\ No newline at end of file
diff --git a/basis/compiler/cfg/ssa/ssa-tests.factor b/basis/compiler/cfg/ssa/ssa-tests.factor
index c53d30af5d..6a3a014f78 100644
--- a/basis/compiler/cfg/ssa/ssa-tests.factor
+++ b/basis/compiler/cfg/ssa/ssa-tests.factor
@@ -5,9 +5,12 @@ compiler.cfg.registers cpu.architecture kernel namespaces sequences
 tools.test vectors ;
 IN: compiler.cfg.ssa.tests
 
-! Reset counters so that results are deterministic w.r.t. hash order
-0 vreg-counter set-global
-0 basic-block set-global
+: reset-counters ( -- )
+    ! Reset counters so that results are deterministic w.r.t. hash order
+    0 vreg-counter set-global
+    0 basic-block set-global ;
+
+reset-counters
 
 V{
     T{ ##load-immediate f V int-regs 1 100 }
@@ -38,7 +41,6 @@ V{
 : test-ssa ( -- )
     cfg new 0 get >>entry
     compute-predecessors
-    compute-dominance
     construct-ssa
     drop ;
 
@@ -67,6 +69,9 @@ V{
     }
 ] [ 2 get instructions>> ] unit-test
 
+: clean-up-phis ( insns -- insns' )
+    [ dup ##phi? [ [ [ [ number>> ] dip ] assoc-map ] change-inputs ] when ] map ;
+
 [
     V{
         T{ ##phi f V int-regs 6 H{ { 1 V int-regs 4 } { 2 V int-regs 5 } } }
@@ -75,5 +80,34 @@ V{
     }
 ] [
     3 get instructions>>
-    [ dup ##phi? [ [ [ [ number>> ] dip ] assoc-map ] change-inputs ] when ] map
+    clean-up-phis
+] unit-test
+
+reset-counters
+
+V{ } 0 test-bb
+V{ } 1 test-bb
+V{ T{ ##peek f V int-regs 0 D 0 } } 2 test-bb
+V{ T{ ##peek f V int-regs 0 D 0 } } 3 test-bb
+V{ T{ ##replace f V int-regs 0 D 0 } } 4 test-bb
+V{ } 5 test-bb
+V{ } 6 test-bb
+
+0 get 1 get 5 get V{ } 2sequence >>successors drop
+1 get 2 get 3 get V{ } 2sequence >>successors drop
+2 get 4 get 1vector >>successors drop
+3 get 4 get 1vector >>successors drop
+4 get 6 get 1vector >>successors drop
+5 get 6 get 1vector >>successors drop
+
+[ ] [ test-ssa ] unit-test
+
+[
+    V{
+        T{ ##phi f V int-regs 3 H{ { 2 V int-regs 1 } { 3 V int-regs 2 } } }
+        T{ ##replace f V int-regs 3 D 0 }
+    }
+] [
+    4 get instructions>>
+    clean-up-phis
 ] unit-test
\ No newline at end of file
diff --git a/basis/compiler/cfg/ssa/ssa.factor b/basis/compiler/cfg/ssa/ssa.factor
index e11701965b..2e76ba35a1 100644
--- a/basis/compiler/cfg/ssa/ssa.factor
+++ b/basis/compiler/cfg/ssa/ssa.factor
@@ -1,19 +1,21 @@
 ! Copyright (C) 2009 Slava Pestov.
 ! See http://factorcode.org/license.txt for BSD license.
-USING: namespaces kernel accessors sequences fry dlists
-deques assocs sets math combinators sorting
+USING: namespaces kernel accessors sequences fry assocs
+sets math combinators
 compiler.cfg
 compiler.cfg.rpo
 compiler.cfg.def-use
 compiler.cfg.renaming
+compiler.cfg.liveness
 compiler.cfg.registers
 compiler.cfg.dominance
 compiler.cfg.instructions ;
 IN: compiler.cfg.ssa
 
-! SSA construction. Predecessors and dominance must be computed first.
+! SSA construction. Predecessors must be computed first.
 
-! This is the classical algorithm based on dominance frontiers:
+! This is the classical algorithm based on dominance frontiers, except
+! we consult liveness information to build pruned SSA:
 ! http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.25.8240
 
 ! Eventually might be worth trying something fancier:
@@ -32,45 +34,22 @@ SYMBOL: inserting-phi-nodes
     '[
         dup instructions>> [
             defs-vregs [
-                _ push-at
+                _ conjoin-at
             ] with each
         ] with each
     ] each-basic-block ;
 
-SYMBOLS: has-already ever-on-work-list work-list ;
-
-: init-insert-phi-nodes ( bbs -- )
-    H{ } clone has-already set
-    [ unique ever-on-work-list set ]
-    [ <hashed-dlist> [ push-all-front ] keep work-list set ] bi ;
-
-: add-to-work-list ( bb -- )
-    dup ever-on-work-list get key? [ drop ] [
-        [ ever-on-work-list get conjoin ]
-        [ work-list get push-front ]
-        bi
-    ] if ;
-
 : insert-phi-node-later ( vreg bb -- )
-    [ predecessors>> over '[ _ ] H{ } map>assoc \ ##phi new-insn ] keep
-    inserting-phi-nodes get push-at ;
-
-: compute-phi-node-in ( vreg bb -- )
-    dup has-already get key? [ 2drop ] [
-        [ insert-phi-node-later ]
-        [ has-already get conjoin ]
-        [ add-to-work-list ]
-        tri
-    ] if ;
+    2dup live-in key? [
+        [ predecessors>> over '[ _ ] H{ } map>assoc \ ##phi new-insn ] keep
+        inserting-phi-nodes get push-at
+    ] [ 2drop ] if ;
 
 : compute-phi-nodes-for ( vreg bbs -- )
-    dup length 2 >= [
-        init-insert-phi-nodes
-        work-list get [
-            dom-frontier [
-                compute-phi-node-in
-            ] with each
-        ] with slurp-deque
+    keys dup length 2 >= [
+        iterated-dom-frontier [
+            insert-phi-node-later
+        ] with each
     ] [ 2drop ] if ;
 
 : compute-phi-nodes ( -- )
@@ -143,4 +122,10 @@ M: ##phi rename-insn
 PRIVATE>
 
 : construct-ssa ( cfg -- cfg' )
-    dup [ compute-defs compute-phi-nodes insert-phi-nodes ] [ rename ] bi ;
\ No newline at end of file
+    {
+        [ ]
+        [ compute-live-sets ]
+        [ compute-dominance ]
+        [ compute-defs compute-phi-nodes insert-phi-nodes ]
+        [ rename ]
+    } cleave ;
\ No newline at end of file