Re: Re: [PATCH 1/5] x86_64: Add support for bcmp using sse2, sse 4_1, avx2, and evex

[Florian Weimer via Libc-alpha <libc-alpha@sourceware.org>]

* Zack Weinberg via Libc-alpha:

> On Tue, Sep 14, 2021, at 8:00 PM, Joseph Myers wrote:
>> bcmp is an obsolescent function that no modern programs should be using, 
>> and it's not in the implementation namespace either so compilers shouldn't 
>> translate memcmp calls to bcmp.
>
> I want to add that glibc has made bcmp an alias for memcmp for many
> years, which means that Linux- or Hurd-specific programs that are
> still using bcmp may have come to depend on its return value
> indicating ordering rather than just equality.  I myself had been
> under the impression that they were *specified* exactly the same,
> until this thread prompted me to double-check the specifications.  As
> such I don't think it's safe for *glibc* to accept patches that
> optimize bcmp separately from memcmp.

That's a very good point.

> I do rather like the idea of a __gnu_memeq() that compilers could
> optimize memcmp calls to, when they can prove that the result is used
> only for its truth value.

Yes, we should use a name in the implementation namespace because even
if we pick an obvious like memequal, it will probably come back under a
different name from the C committee.

Thanks,
Florian