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vulkan failed to create pipeline on mali devices after using spirv shaders compiled by DXC

iculi

I'm working on a UE4 project. By default UE4 compile its shader to spirv binary by hlslcc + glslang, but in this way the generated spirv shader is suboptimal so I want to use shaderconductor(DXC) to compile hlsl directly to spirv (just like what UE5 does: Unreal Engine 5.0 Release Notes | Unreal Engine 5.0 Documentation)

After I use DXC, the project works pretty well on adreno devices, but it will crash on mali deviecs. I have tried these devices, the all failed to create pipeline (both compute ppl and graphics ppl) with VK_ERROR_INITIALIZATION_FAILED:

The khr spec states that create pipeline should only return the following errors:

and also adreno devices works well, so I guess this might be mali driver bugs.

I have no clue what's goes wrong with generated spirv binary and it seems I can't get enough error information from vulkan, so I need to ask help from mali experts.

I can send you the apk that can produce the failure so if you are interested please leave me a email address. Thanks in advance!

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  • +2 Arm Employee Badge in reply to iculi

    Thanks for the shader!

    It appears the problem is with the SPV_GOOGLE_user_type extension, which we do not support, being used. Based on the DXC documentation they will add this if -fspv-reflect is passed -- which UE will pass by default. However, UE5 will also later strip out the use of the extension before passing the shader to the Vulkan driver. If you look in `Engine/Source/Developer/VulkanShaderFormat/Private/VulkanShaderCompiler.cpp` in UE5 you can find the code that does this (look for `bStripReflect`).

    So, I think your best bet here might be to backport the stripping from UE5 to UE4 if you want to try to use DXC in UE4. Hope that helps :) 

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  • +2 Arm Employee Badge in reply to iculi

    Thanks for the shader!

    It appears the problem is with the SPV_GOOGLE_user_type extension, which we do not support, being used. Based on the DXC documentation they will add this if -fspv-reflect is passed -- which UE will pass by default. However, UE5 will also later strip out the use of the extension before passing the shader to the Vulkan driver. If you look in `Engine/Source/Developer/VulkanShaderFormat/Private/VulkanShaderCompiler.cpp` in UE5 you can find the code that does this (look for `bStripReflect`).

    So, I think your best bet here might be to backport the stripping from UE5 to UE4 if you want to try to use DXC in UE4. Hope that helps :) 

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