On Fri, Nov 10, 2017 at 2:09 AM, Connor Abbott <cwabbo...@gmail.com> wrote: > On Thu, Nov 9, 2017 at 7:17 PM, Marek Olšák <mar...@gmail.com> wrote: >> On Fri, Nov 10, 2017 at 12:40 AM, Matt Arsenault <arse...@gmail.com> wrote: >>> >>>> On Nov 10, 2017, at 07:41, Marek Olšák <mar...@gmail.com> wrote: >>>> >>>> Hi, >>>> >>>> This fixes the TCS gl_ClipDistance piglit failure that was uncovered >>>> by a recent LLVM change. The solution is to set volatile on loads >>>> and stores to enforce proper ordering. >>>> >>>> Please review. >>>> >>> >>> >>> Every LDS access certainly should not be volatile. This kills all >>> optimizations, like formation of ds_read2_b32. What ordering issue are you >>> having? >> >> It might be caused by inttoptr(NULL) that we do to declare LDS. There >> is simply no ordering enforced, which is weird. > > As soon as you do inttoptr(NULL), you've generated a poison value (in > LLVM legalese), so LLVM will assume that you never dereference it and > optimize accordingly. I think a GEP instruction without the inbounds > parameter set will get rid of the poison value, although I'm not sure > about the case where the offset is known to be zero. At least, that's > my reading of the langref text for the GEP instruction > (https://llvm.org/docs/LangRef.html#id215). If zero is a valid address > in LDS, then it sounds like LLVM needs to be fixed to disable this > optimization for certain address spaces. On the other hand, if you're > doing inttoptr(NULL) + offset, where "offset" is the result of a > ptrtoint somewhere, you should be doing inttoptr(offset) instead, and > then LLVM should never misbehave.
I don't think that using inttoptr before every load and store would be better than volatile. The must be a better solution. Marek _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev
