compiler.cfg.stacks.vacant: ##call instructions clear the set of overinitialized locations

basis/compiler/cfg/stacks/vacant/vacant-tests.factor

@@ -161,6 +161,17 @@ IN: compiler.cfg.stacks.vacant.tests
     { { 4 { 3 2 1 -3 0 -2 -1 } } { 0 { -1 } } } state>gc-data
 ] unit-test
 
+! ##call clears the overinitialized slots.
+{
+    { -1 { } }
+} [
+    V{
+        T{ ##replace { src 10 } { loc D 0 } }
+        T{ ##inc-d f -1 }
+        T{ ##call }
+    } create-cfg output-stack-map first
+] unit-test
+
 : cfg1 ( -- cfg )
     V{
         T{ ##inc-d f 1 }

basis/compiler/cfg/stacks/vacant/vacant.factor

@@ -68,6 +68,11 @@ M: ##replace visit-insn visit-replace ;
 M: ##peek visit-insn ( state insn -- state' )
     2dup peek-loc-ok? [ drop ] [ vacant-peek ] if ;
 
+M: ##call visit-insn ( state insn -- state' )
+    ! After a word call, we can't trust any overinitialized locations
+    ! to contain valid pointers anymore.
+    drop [ first2 [ 0 >= ] filter 2array ] map ;
+
 : set-gc-map ( state gc-map -- )
     swap state>gc-data concat
     { >>scrub-d >>check-d >>scrub-r >>check-r } write-slots ;