We won't be able to run the compiled program since it will be compiled
for different system. We instead allow passing the CPU features via
CMake option in that case.
Differential Revision: https://reviews.llvm.org/D95203
The feature check should probably be enhanced for non-x86 architectures,
but this change shields them from x86 specific pieces until then.
This patch has been split out from https://reviews.llvm.org/D81533.
Summary:
The patch is not ready yet and is here to discuss a few options:
- How do we customize the implementation? (i.e. how to define `kRepMovsBSize`),
- How do we specify custom compilation flags? (We'd need `-fno-builtin-memcpy` to be passed in),
- How do we build? We may want to test in debug but build the libc with `-march=native` for instance,
- Clang has a brand new builtin `__builtin_memcpy_inline` which makes the implementation easy and efficient, but:
- If we compile with `gcc` or `msvc` we can't use it, resorting on less efficient code generation,
- With gcc we can use `__builtin_memcpy` but then we'd need a postprocess step to check that the final assembly do not contain call to `memcpy` (unlikely but allowed),
- For msvc we'd need to resort on the compiler optimization passes.
Reviewers: sivachandra, abrachet
Subscribers: mgorny, MaskRay, tschuett, libc-commits, courbet
Tags: #libc-project
Differential Revision: https://reviews.llvm.org/D74397
Petr Hosek