Although popcount is a routine that has had huge optimization attention over the years and yields itself to some very cool approaches, our usage of it in Mesa is afaik never on a critical performance path. That may change one day, eg a software rasterizer may find itself doing many popcounts per triangle for some reason, but right now it's not on our performance path. From that point of view, pushing optimizations to gcc is definitely the preferred option at this point.
Keith ________________________________________ From: tom fogal [tfo...@alumni.unh.edu] Sent: Sunday, November 29, 2009 7:12 PM To: Matt Turner Cc: mesa3d-dev@lists.sourceforge.net Subject: Re: [Mesa3d-dev] minor u_math.h speedup fun Matt Turner <matts...@gmail.com> writes: > On Sat, Nov 28, 2009 at 2:13 PM, Yang Zhao <y...@yangman.ca> wrote: > > The speed-up is definitely there, but __builtin_popcount() > > will still be drastically faster when architecture-specific > > optimizations are enabled: > > I don't think this is the case (except for with SSE4's popcnt > instruction, which your CFLAGS seem to be enabling.) > > Even when compiling with the Intel CC, which can undoubtedly > can optimize code for Core 2 better than gcc, fast_bitcount is > significantly faster. IMHO, the best long term solution is to use gcc's builtin, and ping the gcc folks with the implementation and benchmark results of fast_bitcount. If it's really better, they'll eventually adopt it on the platforms where that makes sense. This would benefit a larger community, and would hopefully mean that nobody needs to come across this again in <N> years when common CPUs might be completely different -- Mesa would just benefit transparently from someone in the gcc community noticing the need for a new tuning. -tom ------------------------------------------------------------------------------ Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day trial. Simplify your report design, integration and deployment - and focus on what you do best, core application coding. Discover what's new with Crystal Reports now. http://p.sf.net/sfu/bobj-july _______________________________________________ Mesa3d-dev mailing list Mesa3d-dev@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/mesa3d-dev ------------------------------------------------------------------------------ Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day trial. Simplify your report design, integration and deployment - and focus on what you do best, core application coding. Discover what's new with Crystal Reports now. http://p.sf.net/sfu/bobj-july _______________________________________________ Mesa3d-dev mailing list Mesa3d-dev@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/mesa3d-dev
