Unused GCC builtins

[Florian Weimer]

* Manuel Rigger:

> 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.

You actually need to compile the sources with an instrumented compiler
to discover uses of built-ins.  Not all references will have verbatim,
textual references in source code, but their names are constructed
using preprocessor macros.  This happens for the majority of the
floating-point-related built-ins you listed, I think.