diff --git a/basis/compiler/cfg/linear-scan/allocation/allocation.factor b/basis/compiler/cfg/linear-scan/allocation/allocation.factor
index 908bf2475b..fa10ecfca4 100644
--- a/basis/compiler/cfg/linear-scan/allocation/allocation.factor
+++ b/basis/compiler/cfg/linear-scan/allocation/allocation.factor
@@ -1,9 +1,9 @@
-! Copyright (C) 2008 Slava Pestov.
+! Copyright (C) 2008, 2009 Slava Pestov.
 ! See http://factorcode.org/license.txt for BSD license.
 USING: namespaces sequences math math.order kernel assocs
-accessors vectors fry heaps cpu.architecture combinators
-compiler.cfg.registers
-compiler.cfg.linear-scan.live-intervals ;
+accessors vectors fry heaps cpu.architecture sorting locals
+combinators compiler.cfg.registers
+compiler.cfg.linear-scan.live-intervals hints ;
 IN: compiler.cfg.linear-scan.allocation
 
 ! Mapping from register classes to sequences of machine registers
@@ -27,13 +27,61 @@ SYMBOL: active-intervals
 : delete-active ( live-interval -- )
     dup vreg>> active-intervals-for delq ;
 
-: expire-old-intervals ( n -- )
-    active-intervals swap '[
-        [
-            [ end>> _ < ] partition
-            [ [ deallocate-register ] each ] dip
-        ] assoc-map
-    ] change ;
+! Vector of inactive live intervals
+SYMBOL: inactive-intervals
+
+: inactive-intervals-for ( vreg -- seq )
+    reg-class>> inactive-intervals get at ;
+
+: add-inactive ( live-interval -- )
+    dup vreg>> inactive-intervals-for push ;
+
+! Vector of handled live intervals
+SYMBOL: handled-intervals
+
+: add-handled ( live-interval -- )
+    handled-intervals get push ;
+
+: finished? ( n live-interval -- ? ) end>> swap < ;
+
+: finish ( n live-interval -- keep? )
+    nip [ deallocate-register ] [ add-handled ] bi f ;
+
+: activate ( n live-interval -- keep? )
+    nip add-active f ;
+
+: deactivate ( n live-interval -- keep? )
+    nip add-inactive f ;
+
+: don't-change ( n live-interval -- keep? ) 2drop t ;
+
+! Moving intervals between active and inactive sets
+: process-intervals ( n symbol quots -- )
+    ! symbol stores an alist mapping register classes to vectors
+    [ get values ] dip '[ [ _ cond ] with filter-here ] with each ; inline
+
+: covers? ( insn# live-interval -- ? )
+    ranges>> [ [ from>> ] [ to>> ] bi between? ] with any? ;
+
+: deactivate-intervals ( n -- )
+    ! Any active intervals which have ended are moved to handled
+    ! Any active intervals which cover the current position
+    ! are moved to inactive
+    active-intervals {
+        { [ 2dup finished? ] [ finish ] }
+        { [ 2dup covers? not ] [ deactivate ] }
+        [ don't-change ]
+    } process-intervals ;
+
+: activate-intervals ( n -- )
+    ! Any inactive intervals which have ended are moved to handled
+    ! Any inactive intervals which do not cover the current position
+    ! are moved to active
+    inactive-intervals {
+        { [ 2dup finished? ] [ finish ] }
+        { [ 2dup covers? ] [ activate ] }
+        [ don't-change ]
+    } process-intervals ;
 
 ! Minheap of live intervals which still need a register allocation
 SYMBOL: unhandled-intervals
@@ -66,29 +114,64 @@ SYMBOL: progress
 
 : coalesce ( live-interval -- )
     dup copy-from>> active-interval
-    [ [ add-active ] [ delete-active ] bi* ]
+    [ [ add-active ] [ [ delete-active ] [ add-handled ] bi ] bi* ]
     [ reg>> >>reg drop ]
     2bi ;
 
 ! Splitting
-: find-use ( live-interval n quot -- i elt )
-    [ uses>> ] 2dip curry find ; inline
+: split-range ( live-range n -- before after )
+    [ [ from>> ] dip <live-range> ]
+    [ 1 + swap to>> <live-range> ]
+    2bi ;
 
-: split-before ( live-interval i -- before )
-    [ clone dup uses>> ] dip
-    [ head >>uses ] [ 1- swap nth >>end ] 2bi ;
+: split-last-range? ( last n -- ? )
+    swap to>> <= ;
 
-: split-after ( live-interval i -- after )
-    [ clone dup uses>> ] dip
-    [ tail >>uses ] [ swap nth >>start ] 2bi
-    f >>reg f >>copy-from ;
+: split-last-range ( before after last n -- before' after' )
+    split-range [ [ but-last ] dip suffix ] [ prefix ] bi-curry* bi* ;
 
-: split-interval ( live-interval n -- before after )
-    [ drop ] [ [ > ] find-use drop ] 2bi
-    [ split-before ] [ split-after ] 2bi ;
+: split-ranges ( live-ranges n -- before after )
+    [ '[ from>> _ <= ] partition ]
+    [
+        pick empty? [ drop ] [
+            [ over last ] dip 2dup split-last-range?
+            [ split-last-range ] [ 2drop ] if
+        ] if
+    ] bi ;
+
+: split-uses ( uses n -- before after )
+    '[ _ <= ] partition ;
 
 : record-split ( live-interval before after -- )
-    [ >>split-before ] [ >>split-after ] bi* drop ;
+    [ >>split-before ] [ >>split-after ] bi* drop ; inline
+
+: check-split ( live-interval -- )
+    [ end>> ] [ start>> ] bi - 0 =
+    [ "BUG: splitting atomic interval" throw ] when ; inline
+
+: split-before ( before -- before' )
+    [ [ ranges>> last ] [ uses>> last ] bi >>to drop ]
+    [ compute-start/end ]
+    [ ]
+    tri ; inline
+
+: split-after ( after -- after' )
+    [ [ ranges>> first ] [ uses>> first ] bi >>from drop ]
+    [ compute-start/end ]
+    [ ]
+    tri ; inline
+
+:: split-interval ( live-interval n -- before after )
+    live-interval check-split
+    live-interval clone :> before
+    live-interval clone f >>copy-from f >>reg :> after
+    live-interval uses>> n split-uses before after [ (>>uses) ] bi-curry@ bi*
+    live-interval ranges>> n split-ranges before after [ (>>ranges) ] bi-curry@ bi*
+    live-interval before after record-split
+    before split-before
+    after split-after ;
+
+HINTS: split-interval live-interval object ;
 
 ! Spilling
 SYMBOL: spill-counts
@@ -96,6 +179,9 @@ SYMBOL: spill-counts
 : next-spill-location ( reg-class -- n )
     spill-counts get [ dup 1+ ] change-at ;
 
+: find-use ( live-interval n quot -- i elt )
+    [ uses>> ] 2dip curry find ; inline
+
 : interval-to-spill ( active-intervals current -- live-interval )
     #! We spill the interval with the most distant use location.
     start>> '[ dup _ [ >= ] find-use nip ] { } map>assoc
@@ -108,8 +194,7 @@ SYMBOL: spill-counts
     [ >>spill-to ] [ >>reload-from ] bi-curry bi* ;
 
 : split-and-spill ( new existing -- before after )
-    dup rot start>> split-interval
-    [ record-split ] [ assign-spill ] 2bi ;
+    swap start>> split-interval assign-spill ;
 
 : reuse-register ( new existing -- )
     reg>> >>reg add-active ;
@@ -121,7 +206,7 @@ SYMBOL: spill-counts
     #! of the existing interval again.
     [ reuse-register ]
     [ nip delete-active ]
-    [ split-and-spill [ drop ] [ add-unhandled ] bi* ] 2tri ;
+    [ split-and-spill [ add-handled ] [ add-unhandled ] bi* ] 2tri ;
 
 : spill-new ( new existing -- )
     #! Our new interval will be used after the active interval
@@ -141,37 +226,78 @@ SYMBOL: spill-counts
 : assign-free-register ( new registers -- )
     pop >>reg add-active ;
 
-: assign-register ( new -- )
-    dup coalesce? [
-        coalesce
+: next-intersection ( new inactive -- n )
+    2drop 0 ;
+
+: intersecting-inactive ( new -- live-intervals )
+    dup vreg>> inactive-intervals-for
+    [ tuck next-intersection ] with { } map>assoc ;
+
+: fits-in-hole ( new pair -- )
+    first reuse-register ;
+
+: split-before-use ( new pair -- before after )
+    ! Find optimal split position
+    second split-interval ;
+
+: assign-inactive-register ( new live-intervals -- )
+    ! If there is an interval which is inactive for the entire lifetime
+    ! if the new interval, reuse its vreg. Otherwise, split new so that
+    ! the first half fits.
+    sort-values last
+    2dup [ end>> ] [ second ] bi* < [
+        fits-in-hole
     ] [
-        dup vreg>> free-registers-for
-        [ assign-blocked-register ]
-        [ assign-free-register ]
+        [ split-before-use ] keep
+       '[ _ fits-in-hole ] [ add-unhandled ] bi*
+    ] if ;
+
+: assign-register ( new -- )
+    dup coalesce? [ coalesce ] [
+        dup vreg>> free-registers-for [
+            dup intersecting-inactive
+            [ assign-blocked-register ]
+            [ assign-inactive-register ]
+            if-empty
+        ] [ assign-free-register ]
         if-empty
     ] if ;
 
 ! Main loop
 : reg-classes ( -- seq ) { int-regs double-float-regs } ; inline
 
+: reg-class-assoc ( quot -- assoc )
+    [ reg-classes ] dip { } map>assoc ; inline
+
 : init-allocator ( registers -- )
-    <min-heap> unhandled-intervals set
     [ reverse >vector ] assoc-map free-registers set
-    reg-classes [ 0 ] { } map>assoc spill-counts set
-    reg-classes [ V{ } clone ] { } map>assoc active-intervals set
+    [ 0 ] reg-class-assoc spill-counts set
+    <min-heap> unhandled-intervals set
+    [ V{ } clone ] reg-class-assoc active-intervals set
+    [ V{ } clone ] reg-class-assoc inactive-intervals set
+    V{ } clone handled-intervals set
     -1 progress set ;
 
 : handle-interval ( live-interval -- )
-    [ start>> progress set ]
-    [ start>> expire-old-intervals ]
-    [ assign-register ]
-    tri ;
+    [
+        start>>
+        [ progress set ]
+        [ deactivate-intervals ]
+        [ activate-intervals ] tri
+    ] [ assign-register ] bi ;
 
 : (allocate-registers) ( -- )
     unhandled-intervals get [ handle-interval ] slurp-heap ;
 
+: finish-allocation ( -- )
+    ! Sanity check: all live intervals should've been processed
+    active-intervals inactive-intervals
+    [ get values [ handled-intervals get push-all ] each ] bi@ ;
+
 : allocate-registers ( live-intervals machine-registers -- live-intervals )
     #! This modifies the input live-intervals.
     init-allocator
-    dup init-unhandled
-    (allocate-registers) ;
+    init-unhandled
+    (allocate-registers)
+    finish-allocation
+    handled-intervals get ;
diff --git a/basis/compiler/cfg/linear-scan/assignment/assignment.factor b/basis/compiler/cfg/linear-scan/assignment/assignment.factor
index 0de350c215..4a9b0b231d 100644
--- a/basis/compiler/cfg/linear-scan/assignment/assignment.factor
+++ b/basis/compiler/cfg/linear-scan/assignment/assignment.factor
@@ -25,12 +25,7 @@ TUPLE: active-intervals seq ;
 SYMBOL: unhandled-intervals
 
 : add-unhandled ( live-interval -- )
-    dup split-before>> [
-        [ split-before>> ] [ split-after>> ] bi
-        [ add-unhandled ] bi@
-    ] [
-        dup start>> unhandled-intervals get heap-push
-    ] if ;
+    dup start>> unhandled-intervals get heap-push ;
 
 : init-unhandled ( live-intervals -- )
     [ add-unhandled ] each ;
diff --git a/basis/compiler/cfg/linear-scan/linear-scan-tests.factor b/basis/compiler/cfg/linear-scan/linear-scan-tests.factor
index e0cbe3774f..cf4daa3ab0 100644
--- a/basis/compiler/cfg/linear-scan/linear-scan-tests.factor
+++ b/basis/compiler/cfg/linear-scan/linear-scan-tests.factor
@@ -12,6 +12,60 @@ compiler.cfg.linear-scan.live-intervals
 compiler.cfg.linear-scan.allocation
 compiler.cfg.linear-scan.debugger ;
 
+[
+    { T{ live-range f 1 10 } T{ live-range f 15 15 } }
+    { T{ live-range f 16 20 } }
+] [
+    {
+        T{ live-range f 1 10 }
+        T{ live-range f 15 20 }
+    } 15 split-ranges
+] unit-test
+
+[
+    { T{ live-range f 1 10 } T{ live-range f 15 16 } }
+    { T{ live-range f 17 20 } }
+] [
+    {
+        T{ live-range f 1 10 }
+        T{ live-range f 15 20 }
+    } 16 split-ranges
+] unit-test
+
+[
+    { T{ live-range f 1 10 } }
+    { T{ live-range f 15 20 } }
+] [
+    {
+        T{ live-range f 1 10 }
+        T{ live-range f 15 20 }
+    } 12 split-ranges
+] unit-test
+
+[
+    { T{ live-range f 1 10 } T{ live-range f 15 17 } }
+    { T{ live-range f 18 20 } }
+] [
+    {
+        T{ live-range f 1 10 }
+        T{ live-range f 15 20 }
+    } 17 split-ranges
+] unit-test
+
+[
+    { }
+    { T{ live-range f 1 10 } }
+] [
+    { T{ live-range f 1 10 } } 0 split-ranges
+] unit-test
+
+[
+    { T{ live-range f 0 0 } }
+    { T{ live-range f 1 5 } }
+] [
+    { T{ live-range f 0 5 } } 0 split-ranges
+] unit-test
+
 [ 7 ] [
     T{ live-interval
         { vreg T{ vreg { reg-class int-regs } { n 2 } } }
@@ -44,23 +98,26 @@ compiler.cfg.linear-scan.debugger ;
 
 [
     T{ live-interval
-        { vreg T{ vreg { reg-class int-regs } { n 1 } } }
-        { start 0 }
-        { end 1 }
-        { uses V{ 0 1 } }
+       { vreg T{ vreg { reg-class int-regs } { n 1 } } }
+       { start 0 }
+       { end 1 }
+       { uses V{ 0 1 } }
+       { ranges V{ T{ live-range f 0 1 } } }
     }
     T{ live-interval
-        { vreg T{ vreg { reg-class int-regs } { n 1 } } }
-        { start 5 }
-        { end 5 }
-        { uses V{ 5 } }
+       { vreg T{ vreg { reg-class int-regs } { n 1 } } }
+       { start 5 }
+       { end 5 }
+       { uses V{ 5 } }
+       { ranges V{ T{ live-range f 5 5 } } }
     }
 ] [
     T{ live-interval
-        { vreg T{ vreg { reg-class int-regs } { n 1 } } }
-        { start 0 }
-        { end 5 }
-        { uses V{ 0 1 5 } }
+       { vreg T{ vreg { reg-class int-regs } { n 1 } } }
+       { start 0 }
+       { end 5 }
+       { uses V{ 0 1 5 } }
+       { ranges V{ T{ live-range f 0 5 } } }
     } 2 split-interval
 ] unit-test
 
@@ -70,12 +127,14 @@ compiler.cfg.linear-scan.debugger ;
         { start 0 }
         { end 0 }
         { uses V{ 0 } }
+        { ranges V{ T{ live-range f 0 0 } } }
     }
     T{ live-interval
         { vreg T{ vreg { reg-class int-regs } { n 1 } } }
         { start 1 }
         { end 5 }
         { uses V{ 1 5 } }
+        { ranges V{ T{ live-range f 1 5 } } }
     }
 ] [
     T{ live-interval
@@ -83,6 +142,7 @@ compiler.cfg.linear-scan.debugger ;
         { start 0 }
         { end 5 }
         { uses V{ 0 1 5 } }
+         { ranges V{ T{ live-range f 0 5 } } }
     } 0 split-interval
 ] unit-test
 
@@ -173,7 +233,13 @@ compiler.cfg.linear-scan.debugger ;
 
 [ ] [
     {
-        T{ live-interval { vreg T{ vreg { n 1 } { reg-class int-regs } } } { start 0 } { end 100 } { uses V{ 0 100 } } }
+        T{ live-interval
+           { vreg T{ vreg { n 1 } { reg-class int-regs } } }
+           { start 0 }
+           { end 100 }
+           { uses V{ 0 100 } }
+           { ranges V{ T{ live-range f 0 100 } } }
+        }
     }
     H{ { int-regs { "A" } } }
     check-linear-scan
@@ -181,8 +247,20 @@ compiler.cfg.linear-scan.debugger ;
 
 [ ] [
     {
-        T{ live-interval { vreg T{ vreg { n 1 } { reg-class int-regs } } } { start 0 } { end 10 } { uses V{ 0 10 } } }
-        T{ live-interval { vreg T{ vreg { n 2 } { reg-class int-regs } } } { start 11 } { end 20 } { uses V{ 11 20 } } }
+        T{ live-interval
+           { vreg T{ vreg { n 1 } { reg-class int-regs } } }
+           { start 0 }
+           { end 10 }
+           { uses V{ 0 10 } }
+           { ranges V{ T{ live-range f 0 10 } } }
+        }
+        T{ live-interval
+           { vreg T{ vreg { n 2 } { reg-class int-regs } } }
+           { start 11 }
+           { end 20 }
+           { uses V{ 11 20 } }
+           { ranges V{ T{ live-range f 11 20 } } }
+        }
     }
     H{ { int-regs { "A" } } }
     check-linear-scan
@@ -190,8 +268,20 @@ compiler.cfg.linear-scan.debugger ;
 
 [ ] [
     {
-        T{ live-interval { vreg T{ vreg { n 1 } { reg-class int-regs } } } { start 0 } { end 100 } { uses V{ 0 100 } } }
-        T{ live-interval { vreg T{ vreg { n 2 } { reg-class int-regs } } } { start 30 } { end 60 } { uses V{ 30 60 } } }
+        T{ live-interval
+           { vreg T{ vreg { n 1 } { reg-class int-regs } } }
+           { start 0 }
+           { end 100 }
+           { uses V{ 0 100 } }
+           { ranges V{ T{ live-range f 0 100 } } }
+        }
+        T{ live-interval
+           { vreg T{ vreg { n 2 } { reg-class int-regs } } }
+           { start 30 }
+           { end 60 }
+           { uses V{ 30 60 } }
+           { ranges V{ T{ live-range f 30 60 } } }
+        }
     }
     H{ { int-regs { "A" } } }
     check-linear-scan
@@ -199,8 +289,20 @@ compiler.cfg.linear-scan.debugger ;
 
 [ ] [
     {
-        T{ live-interval { vreg T{ vreg { n 1 } { reg-class int-regs } } } { start 0 } { end 100 } { uses V{ 0 100 } } }
-        T{ live-interval { vreg T{ vreg { n 2 } { reg-class int-regs } } } { start 30 } { end 200 } { uses V{ 30 200 } } }
+        T{ live-interval
+           { vreg T{ vreg { n 1 } { reg-class int-regs } } }
+           { start 0 }
+           { end 100 }
+           { uses V{ 0 100 } }
+           { ranges V{ T{ live-range f 0 100 } } }
+        }
+        T{ live-interval
+           { vreg T{ vreg { n 2 } { reg-class int-regs } } }
+           { start 30 }
+           { end 200 }
+           { uses V{ 30 200 } }
+           { ranges V{ T{ live-range f 30 200 } } }
+        }
     }
     H{ { int-regs { "A" } } }
     check-linear-scan
@@ -208,8 +310,20 @@ compiler.cfg.linear-scan.debugger ;
 
 [
     {
-        T{ live-interval { vreg T{ vreg { n 1 } { reg-class int-regs } } } { start 0 } { end 100 } { uses V{ 0 100 } } }
-        T{ live-interval { vreg T{ vreg { n 2 } { reg-class int-regs } } } { start 30 } { end 100 } { uses V{ 30 100 } } }
+        T{ live-interval
+           { vreg T{ vreg { n 1 } { reg-class int-regs } } }
+           { start 0 }
+           { end 100 }
+           { uses V{ 0 100 } }
+           { ranges V{ T{ live-range f 0 100 } } }
+        }
+        T{ live-interval
+           { vreg T{ vreg { n 2 } { reg-class int-regs } } }
+           { start 30 }
+           { end 100 }
+           { uses V{ 30 100 } }
+           { ranges V{ T{ live-range f 30 100 } } }
+        }
     }
     H{ { int-regs { "A" } } }
     check-linear-scan
@@ -272,31 +386,10 @@ USING: math.private compiler.cfg.debugger ;
     test-cfg first optimize-cfg linear-scan drop
 ] unit-test
 
-[ 0 1 ] [
-    {
-        T{ live-interval
-            { vreg T{ vreg { reg-class int-regs } { n 1 } } }
-            { start 0 }
-            { end 5 }
-            { uses V{ 0 1 5 } }
-        }
-        T{ live-interval
-            { vreg T{ vreg { reg-class int-regs } { n 2 } } }
-            { start 3 }
-            { end 4 }
-            { uses V{ 3 4 } }
-        }
-        T{ live-interval
-            { vreg T{ vreg { reg-class int-regs } { n 3 } } }
-            { start 2 }
-            { end 6 }
-            { uses V{ 2 4 6 } }
-        }
-    } [ clone ] map
-    H{ { int-regs { "A" "B" } } }
-    allocate-registers
-    first split-before>> [ start>> ] [ end>> ] bi
-] unit-test
+: fake-live-ranges ( seq -- seq' )
+    [
+        clone dup [ start>> ] [ end>> ] bi <live-range> 1vector >>ranges
+    ] map ;
 
 ! Coalescing interacted badly with splitting
 [ ] [
@@ -345,7 +438,7 @@ USING: math.private compiler.cfg.debugger ;
             { end 10 }
             { uses V{ 9 10 } }
         }
-    }
+    } fake-live-ranges
     { { int-regs { 0 1 2 3 } } }
     allocate-registers drop
 ] unit-test
@@ -1100,7 +1193,7 @@ USING: math.private compiler.cfg.debugger ;
             { end 109 }
             { uses V{ 103 109 } }
         }
-    }
+    } fake-live-ranges
     { { int-regs { 0 1 2 3 4 } } }
     allocate-registers drop
 ] unit-test
@@ -1193,7 +1286,7 @@ USING: math.private compiler.cfg.debugger ;
             { end 92 }
             { uses V{ 42 45 78 80 92 } }
         }
-    }
+    } fake-live-ranges
     { { int-regs { 0 1 2 3 } } }
     allocate-registers drop
 ] unit-test
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 78ac9428d8..546443b289 100644
--- a/basis/compiler/cfg/linear-scan/live-intervals/live-intervals.factor
+++ b/basis/compiler/cfg/linear-scan/live-intervals/live-intervals.factor
@@ -1,7 +1,7 @@
 ! Copyright (C) 2008, 2009 Slava Pestov.
 ! See http://factorcode.org/license.txt for BSD license.
 USING: namespaces kernel assocs accessors sequences math math.order fry
-compiler.cfg.instructions compiler.cfg.registers
+binary-search compiler.cfg.instructions compiler.cfg.registers
 compiler.cfg.def-use compiler.cfg.liveness compiler.cfg ;
 IN: compiler.cfg.linear-scan.live-intervals
 
@@ -109,6 +109,7 @@ M: ##copy-float compute-live-intervals*
 
 : compute-start/end ( live-interval -- )
     dup ranges>> [ first from>> ] [ last to>> ] bi
+    2dup > [ "BUG: start > end" throw ] when
     [ >>start ] [ >>end ] bi* drop ;
 
 : finish-live-intervals ( live-intervals -- )