Created attachment 35659 [details]
Archive contains wrap-int-[012].cxx and makefile

Ideally, replacing the type "int" with a wrapper class that contains a single "int" value as a member should not impose any performance penalty.  Unfortunately, that is not the case if the wrapper class has a non-default constructor, which it almost certainly will.

The attached archive contains three programs, which can be compiled to assembly language using the included makefile.

wrap-int-0.cxx contains a very simple integer computation.

wrap-int-1.cxx does the same thing, but the "int" type has been replaced by a wrapper class.  The generated assembly instructions are same, so there is no performance penalty for using the wrapper class.

wrap-int-2.cxx is the same as wrap-int-1.cxx except that a constructor has been added to the wrapper class.  One would expect a good optimizer to generate the same code for this program as for the other two programs, but in fact the generated code is a good deal larger.

I'm guessing that what is happening is that if a type has a non-default constructor, the C++ front end treats constants of that type as variables rather than as contstants, so that even simple optimizations like constant folding are no longer performed by that back end.