protonscr

spirv seems wrong for switch-case

dxvkclosed
doitsujin/dxvk#2556 · opened 2022-03-22 by NeoYuAtGF · updated 2022-03-22 · 9 comments · github
NNeoYuAtGF 2022-03-22 github

Hi @doitsujin ,

I met a dx10 dxbc shader, and the dxbc compiler generated spirv seems wrong. there is no break in case0 or case1, so no new label ID is generted, and case0/case1/default all use the same lable ID 60. can you help check, thanks a lot.

DXBC:
vs_4_0
0. dcl_constantBuffer c0[20], dynamicIndexed

  1. dcl_temps 200
  2. dcl_input_sgv v[0].x, vertex_id
  3. dcl_output o[0].xyzw
  4. mov r7, c0[0]
  5. mov o[0].x, vec4(0xca1cca1c, 0xca1cca1c, 0xca1cca1c, 0xca1cca1c)
  6. mov r0, vec4(0x0, 0x0, 0x0, 0x0)
  7. switch r7.x
  8. case 0x0
  9. or r0.x, r0.x, vec4(0x1, 0x1, 0x1, 0x1)
  10. mov o[0].x, r0.x
  11. retc_z r7.y
  12. or r0.x, r0.x, vec4(0x2, 0x2, 0x2, 0x2)
  13. mov o[0].x, r0.x
  14. case 0x1
  15. or r0.x, r0.x, vec4(0x100, 0x100, 0x100, 0x100)
  16. mov o[0].x, r0.x
  17. breakc_z r7.y
  18. or r0.x, r0.x, vec4(0x200, 0x200, 0x200, 0x200)
  19. mov o[0].x, r0.x
  20. breakc_z r7.z
  21. or r0.x, r0.x, vec4(0x400, 0x400, 0x400, 0x400)
  22. mov o[0].x, r0.x
  23. default
  24. or r0.x, r0.x, vec4(0x10000, 0x10000, 0x10000, 0x10000)
  25. mov o[0].x, r0.x
  26. break
  27. endswitch
  28. ret

part of spirv:
56: 8(fvec4) Load 46(r7)
57: 7(float) CompositeExtract 56 0
58: 5(int) Bitcast 57
SelectionMerge 59 None
Switch 58 60
case 0: 60
case 1: 60
60: Label

best wishes
-neo

Ddoitsujin maintainer 2022-03-22 github

Can you please post the DXBC shader binary so that I can actually try and reproduce this?

Ddoitsujin maintainer 2022-03-22 github

Actually yeah, we don't support fallthrough with code. The D3D11 spec calls this out as invalid, and somewhere else it says

D3D10 allowed this, but HLSL never exposed it.

so the question is, how on earth are you generating that shader code?

This is somewhat hard to work around on our end since SPIR-V also does not support this directly.

NNeoYuAtGF 2022-03-22 github

Dx10/dx11 both support fall though, but dx11 has limitation:

The exception is for D3D11, case/default statements that
fall through to the next case/default without a break cannot
have any code in them. D3D10 allowed this, but HLSL never
exposed it. It is still permitted for multiple
case statements (incl default) to appear sequentially
(sharing the same code block).

Hope you can receive the binary.

发件人: Philip Rebohle @.***
发送时间: 2022年3月22日 17:16
收件人: doitsujin/dxvk @.>
抄送: Neo Yu(WH-RD) @.>; Author @.***>
主题: Re: [doitsujin/dxvk] spirv seems wrong for switch-case (Issue #2556)

Actually yeah, we don't support fallthrough with code. The [D3D11 spec](https://microsoft.github.io/DirectX-Specs/d3d/archive/D3D11_3_FunctionalSpec.htm#22.7.12 case (in switch)) calls this out as invalid, and for switch itself it says

D3D10 allowed this, but HLSL never exposed it.

so the question is, how on earth are you generating that shader code?

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Ddoitsujin maintainer 2022-03-22 github

We do support the D3D11 case, just not the fallthrough with code. This is why both cases point to the same label in your shader, since we're assuming that the block between multiple cases is empty.

NNeoYuAtGF 2022-03-22 github

so will you support this for dx10, or we can provide a fix?

Ddoitsujin maintainer 2022-03-22 github

I can try to fix this, but as mentioned I'll need a way to test this with a real binary.

NNeoYuAtGF 2022-03-22 github

thanks a lot, how can i upload the binary, i tried post binary via mail, seems fail

Ddoitsujin maintainer 2022-03-22 github

Thanks, got the mail.

Ddoitsujin maintainer 2022-03-22 github

Should be fixed as of b015cf0bb23c669496379a265dc40170dfb793aa.

Turns out I was wrong about SPIR-V not supporting fallthrough, it actually is legal, although I'm not sure if this is well-tested in current Vulkan drivers.

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