Date: Tue, 20 Sep 2016 19:57:32 +0200 From: Georg Sauthoff <mail@...rg.so> To: musl@...ts.openwall.com Subject: Re: memchr() performance On Mon, Sep 19, 2016 at 07:58:48PM +0200, Szabolcs Nagy wrote: > * Georg Sauthoff <mail@...rg.so> [2016-09-19 15:29:53 +0200]: > > Yes. Sure, ub means that anything can happen, but this case should be ok > > with GCC - if the function is compiled in isolation in its own > > translation unit. > unless you use lto > (which musl does not support now, but ppl are doing this) Yes, with lto there is no isolation. For lto you can do one of the following: - write a version in pure assembler, doesn't have to be harder to read than a C version - use the may_alias attribute (supported at least by GCC/Clang) - apply the memcpy() trick: https://github.com/gsauthof/find-memchr/blob/master/find_avx2_memcpy_impl.cc Best regards Georg
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