 ! Map vregs -> alias classes
 SYMBOL: vregs>acs
 
-: check ( obj -- obj )
-    [ "BUG: static type error detected" throw ] unless* ; inline
- 
+ERROR: vreg-ac-not-set vreg ;
+
 : vreg>ac ( vreg -- ac )
     #! Only vregs produced by ##allot, ##peek and ##slot can
     #! ever be used as valid inputs to ##slot and ##set-slot,
     #! so we assert this fact by not giving alias classes to
     #! other vregs.
-    vregs>acs get at check ;
+    vregs>acs get ?at [ vreg-ac-not-set ] unless ;
 
 ! Map alias classes -> sequence of vregs
 SYMBOL: acs>vregs

M: ##load-immediate analyze-aliases*
    dup [ val>> ] [ dst>> ] bi constants get set-at ;

M: ##load-reference analyze-aliases*
    dup dst>> set-heap-ac ;


    #! value.
    over [ live-slots get at at ] [ 2drop f ] if ;

ERROR: vreg-has-no-slots vreg ;

: load-constant-slot ( value slot# vreg -- )
    live-slots get ?at [ vreg-has-no-slots ] unless set-at ;

: load-slot ( value slot#/f vreg -- )
    over [ load-constant-slot ] [ 3drop ] if ;
