It is time to start using C++ in gcc. gcc was originally written in C. C++ has now advanced to the point where we can reasonably take advantage of the new features that it provides. The most obvious advantage would be in data structures. gcc implements data structures which are awkward to use for different types. With C++ they could become much simpler. The target structure is naturally implemented as a base class, which would simplify target code. The double-wide integer values could be naturally represented as a small class with operators, again simplifying the code and making it easier to understand.
This would be an easy transition, as the code is already almost completely written in the shared subset of C and C++. One of the arguments against converting to C++ is that the code would be less efficient, but it’s not as though the C code would become less efficient because we were compiling with a C++ compiler. Certainly we would have to pay close attention to efficiency with new changes, but that is no different from what we do today.
The other argument against C++ is that the language has too many complicated features. I think that gcc’s review system will ensure that new code is at least as readable as the old code. In any case programmers these days learn C++ in school. It is not so complex that gcc developers can not understand it.
The only real technical difficulty I see is that we would have to make bootstrapping work with the right libstdc++. I’m sure this is possible. We would also have to explicitly make sure that new versions of gcc can be compiled with old versions of gcc. This would be an addition to the release testing.
In the past Richard Stallman has objected to using C++ for gcc. I don’t know who he feels about it today. However, I believe that this sort of decision should be made by the actual developers.
If anybody has a principled argument against using C++ for gcc, I would very much like to hear it.