Are there conclusive studies/experiments on C compilation using a C++ compiler?

Question

I've seen a lot of arguments over the general performance of C code compiled with a C++ compiler -- I'm curious as to whether there are any solid experimental studies buried beneath all the anecdotal flame wars you find in web searches. I'm particularly interested in the GCC suite, but any data points would be interesting. (Comparing the assembly of "Hello, World!" is not as robust as I'd like. :-)

I'm generally assuming you use the "embedded style" flags -- no exceptions or RTTI. I also wouldn't mind knowing if there are studies on the compilation time itself. TIA!

Answer 1

Adding a datapoint (or at least an anecdote):

We were recently writing a math library for a small embedded-like target, and started writing it in C. About halfway through the project, we switched some of the files to C++, largely in order to use templates for some of the functions where we'd otherwise be writing many nearly-identical pieces of code (or else embedding 40-line functions in preprocessor macros).

At the point where we started switching over, we had a very careful look at the generated assembly code (using GCC) on a number of the functions, and confirmed that it was in fact essentially identical whether the file was compiled as C or C++ -- where by "essentially identical" I mean the differences were in things like symbol names and the stuff at the beginning and end of the assembly file; the actual instructions in the middle of the functions were exactly identical.

Sorry that I don't have a more solid answer.

Edit to add, 2013-03-24: Recently I came across an article where Rusty Russell compared performance on GCC compiled with a C compiler and compiled with a C++ compiler, in response to the recent switch to compiling GCC as C++: http://rusty.ozlabs.org/?p=330. The conclusions are interesting: The version compiled with a C++ compiler was very slightly slower; the difference was about 0.3%. However, that was entirely explained by load time differences caused by larger debug info; when he stripped the binaries and removed the debug info, the differences were less than 0.1% -- i.e., essentially indistinguishable from measurement noise.