On Thu, Apr 21, 2016 at 1:15 AM, Iago Toral <ito...@igalia.com> wrote: > On Wed, 2016-04-20 at 14:22 -0700, Matt Turner wrote: >> This reverts commit b449366587b5f3f64c6fb45fe22c39e4bc8a4309. >> >> I removed the pass thinking that it was now not useful, but that was not >> true. I believe I ran shader-db on HSW and saw no results, but HSW does >> not use the unlit centroid workaround code and as a result does not emit >> redundant MOV_DISPATCH_TO_FLAGS instructions. > > I guess this means that dead-code-elimination doesn't really do anything > about this as you initially thought, right?
Right, the sequence of instructions looks like mov_dispatch_to_flags(8) (null):UD, (-f0.0) linterp(8) vgrf66:F, g2:F, g4<0>:F (+f0.0) linterp(8) vgrf66:F, g4:F, g4<0>:F -mov_dispatch_to_flags(8) (null):UD, (-f0.0) linterp(8) vgrf67:F, g2:F, g4<0>:F (+f0.0) linterp(8) vgrf67:F, g4:F, g4<0>:F -mov_dispatch_to_flags(8) (null):UD, (-f0.0) linterp(8) vgrf68:F, g2:F, g5<0>:F (+f0.0) linterp(8) vgrf68:F, g4:F, g5<0>:F And since the subsequent mov_dispatch_to_flags instructions write results that are used, dead_code_eliminate won't remove them. However we know they're dead because they write the same result as before. I'm not sure which (more general) optimization should handle things like that. I guess it's a special case because it's writing to a weird register. _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev
