On 03.12.2009 11:17, Keith Whitwell wrote: > On Wed, 2009-12-02 at 12:46 -0800, Roland Scheidegger wrote: >> On 02.12.2009 18:33, José Fonseca wrote: >>> I've seen strict aliasing assumption causing bugs in other gallium >>> components. It seems endemic to our code. Unless we actively decidee to >>> go and chase the strict aliasing bugs now we should add >>> -fno-strict-aliasing to all our builds. >> Hmm, actually some of them (in mesa at least) seem to be really >> unnecessary. Take the COPY_4FV macro for instance. I replaced that in a >> simple test program (attached) to either just do direct assignment >> without cast, or use memcpy instead. > > That comment was probably true in 1999 -- but possibly not any longer... > >> The results are actually interesting, the comment says cast is done to >> avoid going through fp registers, but looking in the assembly (at least >> with optimization) that doesn't happen anyway, and the generated code is >> actually nearly identical, but in fact it not only triggers >> strict-aliasing warnings but doesn't work correctly (when compiled with >> -O3 or similar parameters invoking -fstrict-aliasing). > > ... > >> Doesn't use 128bit sse moves but looks like an improvement... When using >> no optimization code certainly gets much less readable and the memcpy >> version will call glibc memcpy (which itself will still be optimized >> hence probably faster despite the function call). >> So I'll kill at least this one and just use _mesa_memcpy there, unless >> there are good reasons not to. I think pretty much all compilers should >> have builtin memcpy optimizations. > > I didn't realize COPY_4FV and friends were related to our strict > aliasing problems -- if that's the case, let's kill or reimplement them > straight away. Actually, that was the simplest one, and most other of these macros don't do this. There's also plenty of warnings in the shader/grammar code, apart from that there's actually not that many warnings, at least when not compiling legacy drivers... So I guess getting rid of strict-aliasing issues is doable for gallium.
Roland ------------------------------------------------------------------------------ Join us December 9, 2009 for the Red Hat Virtual Experience, a free event focused on virtualization and cloud computing. Attend in-depth sessions from your desk. Your couch. Anywhere. http://p.sf.net/sfu/redhat-sfdev2dev _______________________________________________ Mesa3d-dev mailing list Mesa3d-dev@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/mesa3d-dev
