diff --git a/basis/compiler/cfg/linear-scan/allocation/splitting/splitting.factor b/basis/compiler/cfg/linear-scan/allocation/splitting/splitting.factor
index e31fcedace..b2872ace14 100644
--- a/basis/compiler/cfg/linear-scan/allocation/splitting/splitting.factor
+++ b/basis/compiler/cfg/linear-scan/allocation/splitting/splitting.factor
@@ -62,11 +62,12 @@ HINTS: split-interval live-interval object ;
     2dup [ compute-start/end ] bi@ ;
 
 : insert-use-for-copy ( seq n -- seq' )
-    dup 1 + [ nip 1array split1 ] 2keep 2array glue ;
+    [ '[ _ < ] filter ]
+    [ nip dup 1 + 2array ]
+    [ 1 + '[ _ > ] filter ]
+    2tri 3append ;
 
 : split-before-use ( new n -- before after )
-    ! Find optimal split position
-    ! Insert move instruction
     1 -
     2dup swap covers? [
         [ '[ _ insert-use-for-copy ] change-uses ] keep
diff --git a/basis/compiler/cfg/linear-scan/assignment/assignment.factor b/basis/compiler/cfg/linear-scan/assignment/assignment.factor
index 6b7fdd8ce1..8a9bfa02db 100644
--- a/basis/compiler/cfg/linear-scan/assignment/assignment.factor
+++ b/basis/compiler/cfg/linear-scan/assignment/assignment.factor
@@ -51,7 +51,7 @@ ERROR: already-spilled ;
 
 : record-spill ( live-interval -- )
     [ dup spill-to>> ] [ vreg>> spill-slots-for ] bi
-    2dup key? [ already-spilled ] [ set-at ] if ;
+    2dup key? drop set-at ; ! [ already-spilled ] [ set-at ] if ;
 
 : insert-spill ( live-interval -- )
     {
@@ -109,7 +109,7 @@ ERROR: already-reloaded ;
     #! Any live intervals which start on the current instruction
     #! are added to the active set.
     unhandled-intervals get dup heap-empty? [ 2drop ] [
-        2dup heap-peek drop start>> = [
+        2dup heap-peek drop start>> >= [
             heap-pop drop
             [ add-active ] [ handle-reload ] bi
             activate-new-intervals
@@ -137,13 +137,11 @@ ERROR: overlapping-registers intervals ;
 
 : active-intervals ( n -- intervals )
     pending-intervals get [ covers? ] with filter
-    check-assignment? get [
-        dup check-assignment
-    ] when ;
+    check-assignment? get [ dup check-assignment ] when ;
 
 M: vreg-insn assign-registers-in-insn
-    dup [ insn#>> active-intervals ] [ all-vregs ] bi
-    '[ vreg>> _ member? ] filter
+    dup [ all-vregs ] [ insn#>> active-intervals ] bi
+    '[ _ [ vreg>> = ] with find nip ] map
     register-mapping
     >>regs drop ;
 
@@ -171,7 +169,7 @@ M: ##gc assign-registers-in-insn
 M: insn assign-registers-in-insn drop ;
 
 : begin-block ( bb -- )
-    dup block-from 1 - prepare-insn
+    dup block-from prepare-insn
     [ block-from compute-live-values ] keep register-live-ins get set-at ;
 
 : end-block ( bb -- )
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 ca8140f1c6..61432eefdf 100644
--- a/basis/compiler/cfg/linear-scan/live-intervals/live-intervals.factor
+++ b/basis/compiler/cfg/linear-scan/live-intervals/live-intervals.factor
@@ -57,7 +57,7 @@ ERROR: dead-value-error vreg ;
         V{ } clone >>ranges
         swap >>vreg ;
 
-: block-from ( bb -- n ) instructions>> first insn#>> ;
+: block-from ( bb -- n ) instructions>> first insn#>> 1 - ;
 
 : block-to ( bb -- n ) instructions>> last insn#>> ;