[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