[libc-dev] __builtin_* vs llvm-libc provided ones?

Siva Chandra via libc-dev libc-dev at lists.llvm.org
Tue Feb 2 08:23:16 PST 2021

+Guillaume Chatelet <gchatelet at google.com>  who will be able to answer this
better for the memory functions. I will shortly also give my answer for the
math function examples.

On Sat, Jan 30, 2021 at 10:01 AM Ebrahim Byagowi <ebraminio at gmail.com>

> There is e.g. __builtin_memcpy and even a __builtin_memcpy_inline in
> clang, and __builtin_memset_inline
> <https://github.com/llvm/llvm-project/blob/6ca54e0/libc/src/string/memory_utils/memset_utils.h#L20-L23> apparently
> is just a TODO right now.
> As __builtin_memcpy for example already has an implementation on llvm
> <https://github.com/llvm/llvm-project/blob/0da15ea/llvm/lib/IR/IRBuilder.cpp#L187-L209>
> but llvm-libc hasn't reused it and implemented it separately, maybe perhaps
> in order to not make llvm-libc a clang buildable only project as maybe some
> builtins aren't present in other compilers.
> My question is what is the plan about the two, accepting the duplication
> of implementations or removing non libc implementation in favor of llvm
> libc provided ones or the reverse way.
> I wonder if is there a future that all or most of the libc entries will
> also be provided by compiler's __builtin_* and maybe __builin_*_inline also
> thus resolving the TODO __builin_memset_inline by just reusing llvm-libc
> implementations somehow on IRBuilder.
> Thanks!
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