On 22/01/18 16:46, Manuel Rigger wrote:
Hi everyone,
As part of my research, we have been analyzing the usage of GCC builtins
in 5,000 C GitHub projects. One of our findings is that many of these
builtins are unused, even though they are described in the documentation
(see https://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html#C-Extensions)
and obviously took time to develop and maintain. I’ve uploaded a CSV
file with the unused builtins to
http://ssw.jku.at/General/Staff/ManuelRigger/unused-builtins.csv.
Details: We downloaded all C projects from GitHub that had more than 80
GitHub stars, which yielded almost 5,000 projects with a total of more
than one billion lines of C code. We filtered GCC, forks of GCC, and
other compilers as we did not want to incorporate internal usages of GCC
builtins or test cases. We extracted all builtin names from the GCC
docs, and also tried to find such names in the source code, which we
considered as builtin usages. We excluded subdirectories with GCC or
Clang, and removed other false positives. In total, we found 320k
builtin usages in these projects, and 3030 unused builtins out of a
total of 6039 builtins.
What is your take on this? Do you believe that some of these unused
builtins could be removed from the GCC docs or deprecated? Or are they
used in special "niche" domains that we did not consider? If yes, do you
think it is worth to maintain them? Are some of them only used in C++
projects? Might it be possible to remove their implementations (which
has already happened for the Cilk Plus builtins)?
We would be glad for any feedback.
- Manuel
Many of these are going to be used automatically by the compiler. You
write "strdup" in your code, and the compiler treats it as
"__builtin_strdup". I don't know that such functions need to be
documented as extensions, but they are certainly in use.
You will also find that a large number of the builtins are for specific
target processors, and projects using them are not going to turn up on
GitHub. They will be used in embedded software that is not open source.
I am sure there are builtins that are rarely or never used - but I doubt
if it is anything like as many as you have identified from this survey.