On 11/30/2018 01:29 PM, Jason Ekstrand wrote: > On Fri, Nov 30, 2018 at 3:18 PM Ian Romanick <[email protected] > <mailto:[email protected]>> wrote: > > On 11/29/2018 07:47 AM, Connor Abbott wrote: > > On Thu, Nov 29, 2018 at 4:22 PM Jason Ekstrand > <[email protected] <mailto:[email protected]>> wrote: > >> > >> Can you provide some context for this? Those rules are already > flagged "inexact" (that's what the ~ means) so they won't apply to > anything that's "precise" or "invariant". > > > > I think the concern is that this isn't allowed in SPIR-V, even without > > exact or invariant. We even go out of our way to do the correct thing > > in the frontend by inserting an "&& a == a" or "|| a != a", but then > > If you're that paranoid about it, why not just mark the operations are > precise? That's literally why it exists. > > > opt_algebraic removes it with another rule and then this rule can flip > > it from ordered to unordered. The spec says that operations don't have > > to produce NaN, but it doesn't say anything on comparisons other than > > the generic "everything must follow IEEE rules" and an entry in the > > table that says "produces correct results." Then again, I can't find > > anything in GLSL allowing these transforms either, so maybe we just > > need to get rid of them. > > What I hear you saying is, "The behavior isn't defined." Unless you can > point to a CTS test or an application that has incorrect behavior, I'm > going to oppose removing this pretty strongly. *Every* GLSL compiler > does this. > > > The test case came from VKD3D which does D3D12 on Vulkan. Someone > (Samuel, maybe?) was going to ask around and see if we can figure out > what D3D12's rules are. It's possible that it requires IEEE or > something close. If that's the case, as I said to Samuel on IRC, we're > probably looking at an extension. I don't think we want a flag like > this that's set per-API.
Why isn't it sufficient to mark the operation as precise? Was that on IRC, and I missed it? It is also possible that we could improve the handling of 'if (!condition)' in the backend to make these transformations less important. I have some patches for that somewhere. They didn't really help with these transformations in place, and I never measured the result without these transformations. _______________________________________________ mesa-dev mailing list [email protected] https://lists.freedesktop.org/mailman/listinfo/mesa-dev
