question: public void markDirty ( Instruction s , Register symb ) { HashSet < Register > set = dirtyMap . get ( s ) ; if ( set == null ) { set = new HashSet < Register > ( 3 ) ; dirtyMap . put ( s , set ) ; } set . add ( symb ) ; }
target:  Records that the real value of a symbolic register is cached in a dirty scratch register at a given instruction that is a GC point.