On Tue, Apr 24, 2018 at 6:42 AM, Ian Romanick <i...@freedesktop.org> wrote:
> On 04/24/2018 05:44 AM, Rob Clark wrote: > > On Tue, Apr 24, 2018 at 4:24 AM, Samuel Iglesias Gonsálvez > > <sigles...@igalia.com> wrote: > >> Hello, > >> > >> Recently, we have found problems between some SPIRV opcodes and NIR. > >> > >> SPIR-V allows opcodes to mix different bit-sizes for their operands, > such as for some bitfield operations and other ops like bitwise shifts. > >> > >> In NIR, when the ALU opcode doesn't have specified bitsizes for their > operands, it is expected to have both the same bitsize (see the assert in > nir_build_alu() at nir_builder.h). I suppose this assumption comes from the > time that NIR were only fed with GLSL IR but now with SPIR-V that assert is > wrong. > >> > >> Instead of adding new variants for the opcodes (such as nir_op_ishl16, > or so) to workaround the issue, I think it is needed to fix this by > removing this assumption from NIR and its validator. I send this email to > ask for ideas and to find the best way to handle this. > >> > > > > Karol hit the same thing (with for example, shift instructions) with > > the work for spv compute/kernel support. I *think* the number of > > special cases isn't too high, so probably vtn should just insert the > > appropriate conversion instruction (ie. u2u32, etc) so that if the src > > bitsize is incorrect it will be converted. > > That's what I was going to suggest. I guess it's possible that some HW > might benefit from using the smaller bit-size, but the code generator > should be able to see through the conversions to get the smaller data. > Agreed. I think most of these case should have no difference between the theoretical new opcode and original + conversion.
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