On Mon, Oct 14, 2019 at 2:35 AM Segher Boessenkool
[off-list ref] wrote:

On Sun, Oct 13, 2019 at 07:51:01PM -0700, Nathan Chancellor wrote:

quoted

r374662 gives LLVM the ability to convert certain loops into a reference
to bcmp as an optimization; this breaks prom_init_check.sh:

When/why does LLVM think this is okay?  This function has been removed
from POSIX over a decade ago (and before that it always was marked as
legacy).

Segher, do you have links for any of the above? If so, that would be
helpful to me. I'm arguing against certain transforms that assume that
one library function is faster than another, when such claims are
based on measurements from one stdlib implementation. (There's others
in the pipeline I'm not too thrilled about, too).

The rationale for why it was added was that memcmp takes a measurable
amount of time in Google's fleet, and most calls to memcmp don't care
about the position of the mismatch; bcmp is lower overhead (or at
least for our libc implementation, not sure about others).
-- 
Thanks,
~Nick Desaulniers