On Tue, 2010-08-10 at 12:43 -0700, Ian Romanick wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > Keith Whitwell wrote: > > On Mon, 2010-08-09 at 23:48 -0700, Eric Anholt wrote: > >> The previous compiler called _mesa_remove_output_reads unconditionally, > >> while the new compiler doesn't. This should be left up to the backend > >> in my opinion, so perhaps a little flag like Shader.EmitNoIfs and > >> friends for r300g to set for now to call this for the Mesa IR generation > >> would be a good solution. > > > > It seems like this represents a change in the semantics of the mesa > > driver interface -- previously mesa had the (perhaps implicit) rule that > > OUT registers were write-only. The glsl2 branch appears not to be > > respecting that. > > > > I don't really mind this as a follow-on change, but it seems like it > > would be cleaner to keep the glsl2 merge as purely a change on one side > > of the interface, not one which requires a change to drivers or the > > interface itself. > > I has always thought that ARB_vp/fp allowed this, but it seems that I > was wrong. I see two options two resolve this: > > 1. Always generate duplicate writes to shadow copies of shader outputs. > Generate all reads from the shadow copies. Rely on the optimizer to > remove the dead writes. > > 2. Add a lowering pass that inserts the shadow copies only for the > shader outputs that are actually read.
> I'm leaning towards option #2 for a couple reasons. I suspect that the > optimizer may not eliminate some of the extra writes. Option #2 also > allows backends that don't need the shadow copies (i.e., i965) to skip > the extra pass. > > On the flip side, I think option #1 may be easier to implement. I think either is fine - it really just boils down to satisfying the constraint by whichever method is easiest. > In either case, I've submitted a bug to track this issue. Someone > should hack up a validator for Mesa IR and TGSI (like the ir_validate > pass). I'm sure there other implicit, undocumented invariant > assumptions sprinkled through the code. Catching deviations from those > sooner rather than later is the winning plan. This has been on my list for a while, Corbin's galahad layer is an ideal place for it to live. Keith _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
