On 11.08.2014 01:38, Alan Modra wrote: > On Sat, Aug 09, 2014 at 08:08:21PM +0200, Branko Čibej wrote: >> The way to fix this is to make sure that the macro >> SVN_UNALIGNED_ACCESS_IS_OK gives the correct answer; and it's OK if >> that answer compiler-specific, not just platform-specific. In other >> words, it's fine if the macro gives a different answer depending on >> GCC vectorizer options. > If it were up to me I'd revert r956593 entirely. Thinking you can > optimise memcpy is just plain wrong-headed,
I fully agree this is the case today. It probably wasn't when the code was written. Still, it makes sense to look at all our unaligned-access-specific code again. > and this is the second bug > found in patterning_copy(). Hmm, actually if you want to optimise > patterning_copy() then something that might make sense is to detect > the overlap case and copy the original repeating sequence multiple > times, rather than copying what has just been written. That is likely > to give better cache performance especially on processors that suffer > from load-hit-store stalls. You're probably right. Back when I wrote the original code (which, IIRC, didn't use any magic unaligned accesses ...), I was more concerned about being able to read what I'd written. :) -- Brane -- Branko Čibej | Director of Subversion WANdisco | Realising the impossibilities of Big Data e. br...@wandisco.com
