[dxvk] Optimize for the d3d9 Strict float emulation path about amdvlk HOT 17 OPEN

@Blisto91 Thanks for your comments. Now I'm investigating this issue on Amdvlk.
A question here:
Do you have any SPIRV generated when "d3d9.floatEmulation = True" or "d3d9.floatEmulation = Strict" ? I want to know if this setting will be reflected in the shader. Then I can do the optimization according to the related flag in SPIRV.
Thanks.

from amdvlk.

Hi there and thank you for the response. I am not personally skilled in this area but I have asked the dxvk devs for assistance when they have a bit of time.

from amdvlk.

I see GPUOpen-Drivers/llpc@e91a935 added an optimization for ((b==0.0 ? 0.0 : a) * (a==0.0 ? 0.0 : b)). But dxvk also emits fma((b==0.0 ? 0.0 : a), (a==0.0 ? 0.0 : b), c) . So unless llpc lowers fma to mul+add, you should also add a pattern that optimizes the fma version to v_fma_legacy_f32/v_mad_legacy_f32. And depending on if you run constant folding before the optimizations, you also want to handle the case where the comparison+select was optimized away for one mul operand, (a * (a==0.0 ? 0.0 : b))/fma(a, (a==0.0 ? 0.0 : b), c), if b is not constant zero.

from amdvlk.

@DadSchoorse Thanks for your comment. Now I have added more patterns as you refer, now the patterns supported is listed below:

1. ((b==0.0 ? 0.0 : a) * (a==0.0 ? 0.0 : b)) ==>fmul_legacy(a,b)
2. a * (a==0.0?0.0:b) or (b==0.0?0.0:a) * b ==>fmul_legacy(a.b)
3. fma((b==0.0 ? 0.0 : a), (a==0.0 ? 0.0 : b), c) ==>fma_legacy(a,b,c)
4. fma(a, (a==0.0 ? 0.0 : b), c) or fma(b==0.0?0.0:a, b, c) ==>fma_legacy(a,b,c)

For 2.3, one more condition is the single operand(a or b) should not be constant zero here.

Please check any missing here. Now my fix is under CI, looking forward to merge and deliver it ASAP.
Thanks.

from amdvlk.

For 2.3, one more condition is the single operand(a or b) should not be constant zero here.

What I've said before may have been a bit ambiguous, so just to make sure: For a * (a==0.0?0.0:b) it's important that b is not zero. So if (b.isConstant() && b.constantValue() != 0.0) { apply_opt(); }, not if (!b.isConstant() || b.constantValue() != 0.0).

Otherwise, your list matches what radv optimizes.

from amdvlk.

Oh, another thing I just thought of, I don't see a bit size check in GPUOpen-Drivers/llpc@e91a935 . v_mul_legacy_f32/v_fma_legacy_f32 are 32bit only.

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