According to the referenced bug report, gcc-4.5 and newer do not inline memcmp(). I see no difference in performance of ipers with llvmpipe on a Sandybridge (which does not have "Enhanced REP MOVSB/STOSB") by removing this flag.
I attempted to confirm the problem with gcc-4.4, but it fails to compile for quite a few different reasons.
5353855 mesa: Drop -fno-builtin-memcmp.
configure.ac | 8 --------
1 file changed, 8 deletions(-)
Upstream: cgit.freedesktop.org