diff --git a/basis/compiler/cfg/gc-checks/gc-checks.factor b/basis/compiler/cfg/gc-checks/gc-checks.factor
index 090283410f..8435a231e6 100644
--- a/basis/compiler/cfg/gc-checks/gc-checks.factor
+++ b/basis/compiler/cfg/gc-checks/gc-checks.factor
@@ -10,7 +10,7 @@ IN: compiler.cfg.gc-checks
 
 : insert-gc-check ( basic-block -- )
     dup gc? [
-        [ i i f f \ ##gc new-insn prefix ] change-instructions drop
+        [ i i f \ ##gc new-insn prefix ] change-instructions drop
     ] [ drop ] if ;
 
 : insert-gc-checks ( cfg -- cfg' )
diff --git a/basis/compiler/cfg/instructions/instructions.factor b/basis/compiler/cfg/instructions/instructions.factor
index 8e2d2ff75e..56f0452d1a 100644
--- a/basis/compiler/cfg/instructions/instructions.factor
+++ b/basis/compiler/cfg/instructions/instructions.factor
@@ -220,7 +220,7 @@ INSN: ##compare-imm < ##binary-imm cc temp ;
 INSN: ##compare-float-branch < ##conditional-branch ;
 INSN: ##compare-float < ##binary cc temp ;
 
-INSN: ##gc { temp1 vreg } { temp2 vreg } live-registers live-spill-slots ;
+INSN: ##gc { temp1 vreg } { temp2 vreg } live-values ;
 
 ! Instructions used by machine IR only.
 INSN: _prologue stack-frame ;
diff --git a/basis/compiler/cfg/linear-scan/assignment/assignment.factor b/basis/compiler/cfg/linear-scan/assignment/assignment.factor
index 0956b7263f..0ade81311a 100644
--- a/basis/compiler/cfg/linear-scan/assignment/assignment.factor
+++ b/basis/compiler/cfg/linear-scan/assignment/assignment.factor
@@ -105,7 +105,7 @@ ERROR: already-reloaded ;
 GENERIC: assign-registers-in-insn ( insn -- )
 
 : register-mapping ( live-intervals -- alist )
-    [ [ vreg>> ] [ reg>> ] bi ] { } map>assoc ;
+    [ [ vreg>> ] [ reg>> ] bi ] H{ } map>assoc ;
 
 : all-vregs ( insn -- vregs )
     [ defs-vregs ] [ temp-vregs ] [ uses-vregs ] tri 3append ;
@@ -130,19 +130,22 @@ M: vreg-insn assign-registers-in-insn
     register-mapping
     >>regs drop ;
 
-: compute-live-registers ( insn -- regs )
+: compute-live-registers ( insn -- assoc )
     [ active-intervals ] [ temp-vregs ] bi
     '[ vreg>> _ memq? not ] filter
     register-mapping ;
 
-: compute-live-spill-slots ( -- spill-slots )
+: compute-live-spill-slots ( -- assocs )
     spill-slots get values
-    [ [ vreg>> swap ] { } assoc-map-as ] map concat ;
+    [ [ vreg>> swap <spill-slot> ] H{ } assoc-map-as ] map ;
+
+: compute-live-values ( insn -- assoc )
+    [ compute-live-spill-slots ] dip compute-live-registers suffix
+    assoc-combine ;
 
 M: ##gc assign-registers-in-insn
     dup call-next-method
-    dup compute-live-registers >>live-registers
-    compute-live-spill-slots >>live-spill-slots
+    dup compute-live-values >>live-values
     drop ;
 
 M: insn assign-registers-in-insn drop ;
diff --git a/basis/compiler/cfg/linearization/linearization.factor b/basis/compiler/cfg/linearization/linearization.factor
index 8165553a28..15e7cef553 100755
--- a/basis/compiler/cfg/linearization/linearization.factor
+++ b/basis/compiler/cfg/linearization/linearization.factor
@@ -57,41 +57,31 @@ M: ##dispatch linearize-insn
     [ successors>> [ number>> _dispatch-label ] each ]
     bi* ;
 
-: gc-root-registers ( n live-registers -- n )
+: (compute-gc-roots) ( n live-values -- n )
     [
-        [ second 2array , ]
-        [ first reg-class>> reg-size + ]
-        2bi
-    ] each ;
+        [ nip 2array , ]
+        [ drop reg-class>> reg-size + ]
+        3bi
+    ] assoc-each ;
 
-: gc-root-spill-slots ( n live-spill-slots -- n )
+: oop-values ( regs -- regs' )
+    [ drop reg-class>> int-regs eq? ] assoc-filter ;
+
+: data-values ( regs -- regs' )
+    [ drop reg-class>> double-float-regs eq? ] assoc-filter ;
+
+: compute-gc-roots ( live-values -- alist )
     [
-        dup first reg-class>> int-regs eq? [
-            [ second <spill-slot> 2array , ]
-            [ first reg-class>> reg-size + ]
-            2bi
-        ] [ drop ] if
-    ] each ;
-
-: oop-registers ( regs -- regs' )
-    [ first reg-class>> int-regs eq? ] filter ;
-
-: data-registers ( regs -- regs' )
-    [ first reg-class>> double-float-regs eq? ] filter ;
-
-:: compute-gc-roots ( live-registers live-spill-slots -- alist )
-    [
-        0
+        [ 0 ] dip
         ! we put float registers last; the GC doesn't actually scan them
-        live-registers oop-registers gc-root-registers
-        live-spill-slots gc-root-spill-slots
-        live-registers data-registers gc-root-registers
+        [ oop-values (compute-gc-roots) ]
+        [ data-values (compute-gc-roots) ] bi
         drop
     ] { } make ;
 
-: count-gc-roots ( live-registers live-spill-slots -- n )
+: count-gc-roots ( live-values -- n )
     ! Size of GC root area, minus the float registers
-    [ oop-registers length ] bi@ + ;
+    oop-values assoc-size ;
 
 M: ##gc linearize-insn
     nip
@@ -99,11 +89,11 @@ M: ##gc linearize-insn
         [ temp1>> ]
         [ temp2>> ]
         [
-            [ live-registers>> ] [ live-spill-slots>> ] bi
+            live-values>>
             [ compute-gc-roots ]
             [ count-gc-roots ]
             [ gc-roots-size ]
-            2tri
+            tri
         ] tri
         _gc
     ] with-regs ;
diff --git a/basis/compiler/cfg/stack-frame/stack-frame.factor b/basis/compiler/cfg/stack-frame/stack-frame.factor
index 5cb5762b78..9eb6d27521 100644
--- a/basis/compiler/cfg/stack-frame/stack-frame.factor
+++ b/basis/compiler/cfg/stack-frame/stack-frame.factor
@@ -34,8 +34,8 @@ spill-counts ;
 
 : gc-root-offset ( n -- n' ) gc-root-base + ;
 
-: gc-roots-size ( live-registers live-spill-slots -- n )
-    [ keys [ reg-class>> reg-size ] sigma ] bi@ + ;
+: gc-roots-size ( live-values -- n )
+    keys [ reg-class>> reg-size ] sigma ;
 
 : (stack-frame-size) ( stack-frame -- n )
     [