[SelectionDAG] Allow the user to specify a memeq function.

Authored by courbet on Mar 8 2019, 1:07 AM.


[SelectionDAG] Allow the user to specify a memeq function.

Right now, when we encounter a string equality check,
e.g. if (memcmp(a, b, s) == 0), we try to expand to a comparison if s is a
small compile-time constant, and fall back on calling memcmp() else.

This is sub-optimal because memcmp has to compute much more than

This patch replaces memcmp(a, b, s) == 0 by bcmp(a, b, s) == 0 on platforms
that support bcmp.

bcmp can be made much more efficient than memcmp because equality
compare is trivially parallel while lexicographic ordering has a chain

Subscribers: fedor.sergeev, jyknight, ckennelly, gchatelet, llvm-commits

Differential Revision: https://reviews.llvm.org/D56593

llvm-svn: 355672