compiler.cfg.linear-scan.allocation: fix broken spill slot reuse logic

basis/compiler/cfg/linear-scan/allocation/coalescing/coalescing.factor

@@ -1,6 +1,6 @@
 ! Copyright (C) 2009 Slava Pestov.
 ! See http://factorcode.org/license.txt for BSD license.
-USING: accessors kernel sequences
+USING: accessors kernel sequences namespaces assocs fry
 combinators.short-circuit
 compiler.cfg.linear-scan.live-intervals
 compiler.cfg.linear-scan.allocation.state ;
@@ -20,9 +20,16 @@ IN: compiler.cfg.linear-scan.allocation.coalescing
         [ avoids-inactive-intervals? ]
     } 1&& ;
 
+: reuse-spill-slot ( old new -- )
+    [ vreg>> spill-slots get at ] dip '[ _ vreg>> spill-slots get set-at ] when* ;
+
+: reuse-register ( old new -- )
+    reg>> >>reg drop ;
+
+: (coalesce) ( old new -- )
+    [ add-active ] [ [ delete-active ] [ add-handled ] bi ] bi* ;
+
 : coalesce ( live-interval -- )
     dup copy-from>> active-interval
-    [ [ add-active ] [ [ delete-active ] [ add-handled ] bi ] bi* ]
-    [ reg>> >>reg drop ]
-    2bi ;
+    [ reuse-spill-slot ] [ reuse-register ] [ (coalesce) ] 2tri ;
  

basis/compiler/cfg/linear-scan/allocation/spilling/spilling.factor

@@ -38,10 +38,10 @@ ERROR: bad-live-ranges interval ;
     } 2cleave ;
 
 : assign-spill ( live-interval -- )
-    dup assign-spill-slot >>spill-to f >>split-next drop ;
+    dup vreg>> assign-spill-slot >>spill-to f >>split-next drop ;
 
 : assign-reload ( live-interval -- )
-    dup assign-spill-slot >>reload-from drop ;
+    dup vreg>> assign-spill-slot >>reload-from drop ;
 
 : split-and-spill ( live-interval n -- before after )
     split-for-spill 2dup [ assign-spill ] [ assign-reload ] bi* ;

basis/compiler/cfg/linear-scan/allocation/state/state.factor

@@ -126,18 +126,8 @@ SYMBOL: spill-counts
 ! Mapping from vregs to spill slots
 SYMBOL: spill-slots
 
-DEFER: assign-spill-slot
-
-: compute-spill-slot ( live-interval -- n )
-    dup copy-from>>
-    [ assign-spill-slot ]
-    [ vreg>> reg-class>> next-spill-slot ] ?if ;
-
-: assign-spill-slot ( live-interval -- n )
-    dup vreg>> spill-slots get at [ ] [
-        [ compute-spill-slot dup ] keep
-        vreg>> spill-slots get set-at
-    ] ?if ;
+: assign-spill-slot ( vreg -- n )
+    spill-slots get [ reg-class>> next-spill-slot ] cache ;
 
 : init-allocator ( registers -- )
     registers set