Refactor WIDE_READ to allow finer control over high-performance function selection (#165613)
[This is more of a straw-proposal than a ready-for-merging PR. I got
started thinking about what this might look like, and ended up just
implementing something as a proof-of-concept. Totally open to other
methods an ideas.]
As we implement more high-performance string-related functions, we have
found a need for better control over their selection than the big-hammer
LIBC_CONF_STRING_LENGTH_WIDE_READ. For example, I have a memchr
implementation coming, and unless I implement it in every variant, a
simple binary value doesn't work.
This PR makes gives finer-grained control over high-performance
functions than the generic LIBC_CONF_UNSAFE_WIDE_READ option. For any
function they like, the user can now select one of four implementations
at build time:
1. element, which reads byte-by-byte (or wchar by wchar)
2. wide, which reads by unsigned long
3. generic, which uses standard clang vector implemenations, if
available
4. arch, which uses an architecture-specific implemenation
(Reading the code carefully, you may note that a user can actually
specify any namespace they want, so we aren't technically limited to
those 4.)
We may also want to switch from command-line #defines as it is currently
done, to something more like
llvm-project/llvm/include/llvm/Config/llvm-config.h.cmake, and
#including the resulting file, which would move quite a bit of
complexity out of the command-line. But that's a future problem.
NOKEYCHECK=True
GitOrigin-RevId: 8701c2a9106bcf4b9c1178125b56958f9aab7faf
11 files changed
