On Wed, Apr 11, 2012 at 4:24 AM, Lawrence Crowl <cr...@google.com> wrote: > On 4/10/12, Jakub Jelinek <ja...@redhat.com> wrote: >> That when stepping through code in the debugger you keep >> enterring/exiting these one liner inlines, most of them really >> should be at least by default considered just as normal statements >> (e.g. glibc heavily uses artificial attribute for those, still >> gdb doesn't hide those by default). > > You do want to step into those inline functions, except when you do. > In the short term, we can make the debugger behave as though they did > not exist. In the longer term, we really want debugging tools that > help C++ programmers. One way to get there is to use C++ ourselves.
Fix the debugger first please. >> > The above is just quickly cooked up examples. A carefully >> > designed C++ based API can be self documenting and make the >> > client code very readable. It is hard to believe that there is >> > no room for improvement in GCC. >> >> Do you have examples? E.g. I haven't touched gold, because, >> while it is a new C++ codebase, looks completely unreadable to >> me, similarly libdw C++ stuff. A carefully designed C based API >> can be self documenting and make the code very readable as well, >> often more so. > > If you just look at any decently sized code base, it'll look pretty > much unreadable. The question is how quickly can someone who learns > the base vocabulary can produce reasonable modifications. > > There are many places where C++ can help substantially. For example: > > () The C++ postfix member function call syntax means that following > a chain of attributes is a linear read of the expression. With C > function call syntax, you need to read the expression inside out. It's a matter of what you are used to (consider LISP). > () C++ has both overloaded functions and member functions, so you can > use the same verb to talk about several different kinds of objects. > With C function names, we have to invent a new function name for > each type. Such names are longer and burden both the author and > the reader of the code. Agreed. Function overloading is one of the nice things that does not automatically make the code-base look "partial C++". Likewise operator overloading can make things like bit_offset = double_int_add (bit_offset, tree_to_double_int (DECL_FIELD_BIT_OFFSET (field))); be just bit_offset = bit_offset + DECL_FIELD_BIT_OFFSET (field); it still looks like C but with some C++ "magic". > () Standard C++ idioms enable mashing program components with ease. > The C++ standard library is based on mixing and matching algorithms > and data structures, via the common idiom of iterators. Sort-of agreed. Though iterator-style (and more so functor style) was never one of my favorite. > () The overloadable operator new means that memory can be > _implicitly_ allocated in the right place. Implicit allocation is bad. In a compiler you want to _see_ where you spend memory. > () Constructors and destructors reduce the number of places in the > code where you need to do explicit memory management. Without garbage > collection, leaks are less frequent. With garbage collection, you > have much less active garbage, and can run longer between collection > runs. Indeed, a conservative collector would be sufficient. Time will tell. > () Constructors and destructors also neatly handle actions that > must occur in pairs. The classic example is mutex lock and unlock. > Within GCC, timevar operations need to happen in pairs. Agreed. > () Class hierarchies (even without virtual functions) can directly > represent type relationships, which means that a debugger dump of > a C++ type has little unnecessary information, as opposed to the > present union of structs approach with GCC trees. In GCC trees only the "base" is a union, and it is so as implementation detail. That gdb does not grok a 'tree' well is because gdb is stupid. All the information is there. > () Class hierarchies also mean that programmers can distinguish > in the pointer types that a function needs a decl parameter, > without having to say 'all trees' versus 'a very specific tree'. > The static type checking avoids run-time bugs. True. In a very limited set of cases. C++ is not powerful enough to express pointer-to-everything-that-would-be-considered-a-gimple-val. Maybe C++ is not the right choice after all? (I suppose C++ concepts would have helped here? pointer-to-tree-that-fulfils-is_gimple_val ... (though is_gimple_val is not be a static property). > I have written compilers in both C and C++. I much prefer the > latter. Did you ever try to convert an existing large C codebase to C++? I would not expect a very good result and rather start from scratch. So I don't see that we ever arrive (or want to arrive) at a pure C++-style GCC. Instead I expect we end up (and desire to end up) with GCC compiled with a C++ compiler that uses C++ features to make the existing style more readable and maintainable. Richard. > -- > Lawrence Crowl