Global write barrier elimination tracks newly allocated objects

basis/compiler/cfg/write-barrier/write-barrier-tests.factor

@@ -93,6 +93,24 @@ cfg new 1 get >>entry 0 set
     T{ ##set-slot-imm f 2 1 3 4 }
 } ] [ 2 get instructions>> ] unit-test
 
+V{
+    T{ ##allot f 1 }
+} 1 test-bb
+V{
+    T{ ##set-slot-imm f 2 1 3 4 }
+    T{ ##write-barrier f 1 2 3 }
+} 2 test-bb
+1 get 2 get 1vector >>successors drop
+cfg new 1 get >>entry 0 set
+
+[ ] [ 0 [ eliminate-write-barriers ] change ] unit-test
+[ V{
+    T{ ##allot f 1 }
+} ] [ 1 get instructions>> ] unit-test
+[ V{
+    T{ ##set-slot-imm f 2 1 3 4 }
+} ] [ 2 get instructions>> ] unit-test
+
 V{
     T{ ##set-slot-imm f 2 1 3 4 }
     T{ ##write-barrier f 1 2 3 }

basis/compiler/cfg/write-barrier/write-barrier.factor

@@ -36,12 +36,15 @@ FORWARD-ANALYSIS: safe
 : has-allocation? ( bb -- ? )
     instructions>> [ { [ ##allocation? ] [ ##call? ] } 1|| ] any? ;
 
+GENERIC: safe-slot ( insn -- slot ? )
+M: object safe-slot drop f f ;
+M: ##write-barrier safe-slot src>> t ;
+M: ##allot safe-slot dst>> t ;
+
 M: safe-analysis transfer-set
     drop [ H{ } assoc-clone-like ] dip
     instructions>> over '[
-        dup ##write-barrier? [
+        safe-slot [ _ conjoin ] [ drop ] if
-            src>> _ conjoin
-        ] [ drop ] if
     ] each ;
 
 M: safe-analysis join-sets