On Sat, Mar 11, 2017 at 9:50 AM, Jason Ekstrand <ja...@jlekstrand.net> wrote: > > > As I said at the top, I'm really not going for NIR or nothing. I agree > that GLSL has advantages for chips like r600 which badly needs emulation > and isn't moving to NIR any time soon. Also, fp64 isn't a requirement in > Vulkan and, given that Vulkan covers both desktop and mobile, likely won't > be any time soon. (In fact, if someone wanted Vulkan FP64 on hardware that > didn't support it, I'd be tempted to tell them to pay someone to write a > layer.) However, *if* we decide that emulated fp64 is better on, for > instance Ivy Bridge, *and* we had customers that cared about it (I don't > know of any), then doing it in NIR could yield substantially better results > (depending on initial shader quality) due to being able to run > nir_opt_algebraic first. Those are a lot of ifs so maybe I'm suggesting we > design for a non-use-case, but I really don't want to paint ourselves into > a corner that we have to crawl out of 2 years from now. >
Chatting with people on IRC this morning, I realized there's a killer argument for why we *need* NIR support: SPIR-V on OpenGL. As soon as you expose the GL_ARB_spirv extension on an OpenGL 4.0+ driver, you must support fp64. If we ever need emulated fp64 in such a driver, the lowering has to be done in NIR because there is no GLSL IR in the path.
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