tigress --Environment=x86_64:Darwin:Clang:5.1 --Verbosity=1 --FilePrefix=x \
   --FilePrefix=v1 \
   --Transform=Virtualize --Functions=fib --VirtualizeDispatch=ifnest \
   --Transform=CleanUp --CleanUpKinds=annotations \
   --out=gen/v1.c test1.c

tigress --Environment=x86_64:Darwin:Clang:5.1 --Verbosity=1 --FilePrefix=x \
   --FilePrefix=v2 \
   --Transform=Virtualize --Functions=fib --VirtualizeDispatch=ifnest \
   --Transform=CleanUp --CleanUpKinds=annotations \
   --out=gen/virtualize-virtualize-prefix.c gen/v1.c