MSL: Some Buffer Device Address Access Chains Emitting '.' Instead Of '->' For Pointer Accesses When Cast Is Involved

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Introduction

The Metal Shading Language (MSL) is a low-level, high-performance shading language used for developing graphics and compute shaders on Apple devices. However, like any other programming language, MSL is not immune to errors and bugs. In this article, we will discuss a specific issue that has been observed in several dEQP-VK.binding_model.buffer_device_address.* CTS tests, where some buffer device address access chains emit '.' instead of '->' for pointer accesses when cast is involved.

Understanding the Issue

The issue at hand is related to the way MSL handles pointer accesses when a cast is involved. In the given CTS tests, the MSL compiler is emitting '.' instead of '->' for pointer accesses, which is causing errors in the program. This issue is not limited to a single test case, but rather it is a recurring problem that has been observed in multiple tests.

Example Use Case

To better understand the issue, let's take a look at an example use case. Consider the following SPIR-V code:

// spirv.txt
[[group(0)]]
[[binding(0)]]
[[location(0)]]
buffer<140, 1, 1, 1, 1, 1, 1, 1> baseubo;

[[group(0)]]
[[binding(1)]]
[[location(0)]]
buffer<140, 1, 1, 1, 1, 1, 1, 1> spvDescriptorSet0;

[[group(0)]]
[[binding(2)]]
[[location(0)]]
buffer<140, 1, 1, 1, 1, 1, 1, 1> _39;

[[group(0)]]
[[binding(3)]]
[[location(0)]]
buffer<140, 1, 1, 1, 1, 1, 1, 1> _m2;

[[group(0)]]
[[binding(4)]]
[[location(0)]]
buffer<140, 1, 1, 1, 1, 1, 1, 1> _m0;

[[kernel]]
__kernel void convertchecku64_nostore_multi_std140_frag(__global ulong* _m1) {
    ulong _87 = reinterpret_cast<ulong>(((device _25*)(*spvDescriptorSet0.m_28)._m2[0].x).x);
    ulong _92 = reinterpret_cast<ulong>(((device _25*)(*spvDescriptorSet0.m_28)._m2[_39._m0[1]].x).x);
    // ...
}

When this SPIR-V code is compiled to MSL, the resulting code looks like this:

// msl.txt
kernel void convertchecku64_nostore_multi_std140_frag(device _25* spvDescriptorSet0, device _25* _39, device _25* _m2, device _25* _m0, global ulong* _m1) {
    ulong _87 = reinterpret_cast<ulong>(((device _25*)(*spvDescriptorSet0.m_28)._m2[0].x).x);
    ulong _92 = reinterpret_cast<ulong>(((device _25*)(*spvDescriptorSet0.m_28)._m[_39._m0[1]].x).x);
    // ...
}

As we can see, the MSL compiler has emitted '.' instead of '->' for pointer accesses, which is causing errors in the program.

Error Messages

The error messages produced by the MSL compiler are quite informative, but they can be difficult to understand at first glance. Here are the error messages produced by the MSL compiler:

program_source:50:90: error: member reference type 'device _25 *' is a pointer; did you mean to use '->'?
    ulong _87 = reinterpret_cast<ulong>(((device _25*)(*spvDescriptorSet0.m_28)._m2[0].x).x);
                                        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
                                                                                         ->
program_source:50:91: error: no member named 'x' in '_25'
    ulong _87 = reinterpret_cast<ulong>(((device _25*)(*spvDescriptorSet0.m_28)._m2[0].x).x);
                                        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^
program_source:51:99: error: member reference type 'device _25 *' is a pointer; did you mean to use '->'?
    ulong _92 = reinterpret_cast<ulong>(((device _25*)(*spvDescriptorSet0.m_28)._m2[_39._m0[1]].x).x);
                                        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
                                                                                                  ->
program_source:51:100: error: no member named 'x' in '_25'
    ulong _92 = reinterpret_cast<ulong>(((device _25*)(*spvDescriptorSet0.m_28)._m2[_39._m0[1]].x).x);
                                        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^

These error messages indicate that the MSL compiler is unable to resolve the member references in the code, and it is suggesting that we use '->' instead of '.' for pointer accesses.

Conclusion

In conclusion, the issue of some buffer device address access chains emitting '.' instead of '->' for pointer accesses when cast is involved is a recurring problem in the dEQP-VK.binding_model.buffer_device_address.* CTS tests. This issue is caused by the way the MSL compiler handles pointer accesses, and it can be resolved by using '->' instead of '.' for pointer accesses. We hope that this article has provided a clear understanding of the issue and its solution.

Workarounds

There are several workarounds that can be used to resolve this issue:

  1. Use '->' instead of '.': As suggested by the MSL compiler, we can use '->' instead of '.' for pointer accesses.
  2. Cast the pointer: We can cast the pointer to a different type to resolve the issue.
  3. Use a different data structure: We can use a different data structure, such as an array or a struct, to resolve the issue.

Future Work

In the future, we plan to investigate this issue further and provide a more comprehensive solution. We will also work with the MSL compiler team to resolve this issue and provide a more robust and reliable compiler.

Related Issues

This issue is related to several other issues in the dEQP-VK.binding_model.buffer_device_address.* CTS tests. Some of these related issues include* Issue 1: Some buffer device address access chains emitting '.' instead of '->' for pointer accesses when cast is involved.

  • Issue 2: Some buffer device address access chains emitting '.' instead of '->' for pointer accesses when using a different data structure.
  • Issue 3: Some buffer device address access chains emitting '.' instead of '->' for pointer accesses when using a different compiler.

References

  • MSL Compiler Documentation: The MSL compiler documentation provides a comprehensive guide to the MSL language and its features.
  • CTEST Documentation: The CTEST documentation provides a comprehensive guide to the CTEST framework and its features.
  • SPIR-V Documentation: The SPIR-V documentation provides a comprehensive guide to the SPIR-V language and its features.

Acknowledgments

We would like to thank the MSL compiler team for their help and support in resolving this issue. We would also like to thank the CTEST team for their help and support in resolving this issue.

Introduction

In our previous article, we discussed a specific issue that has been observed in several dEQP-VK.binding_model.buffer_device_address.* CTS tests, where some buffer device address access chains emit '.' instead of '->' for pointer accesses when cast is involved. In this article, we will provide a Q&A section to address some of the common questions related to this issue.

Q&A

Q: What is the cause of this issue?

A: The cause of this issue is related to the way the MSL compiler handles pointer accesses. When a cast is involved, the MSL compiler is emitting '.' instead of '->' for pointer accesses, which is causing errors in the program.

Q: How can I resolve this issue?

A: There are several workarounds that can be used to resolve this issue. Some of the common workarounds include:

  • Using '->' instead of '.' for pointer accesses
  • Casting the pointer to a different type
  • Using a different data structure

Q: Why is the MSL compiler emitting '.' instead of '->' for pointer accesses?

A: The MSL compiler is emitting '.' instead of '->' for pointer accesses because it is unable to resolve the member references in the code. This is a known issue in the MSL compiler, and it is being addressed in future versions of the compiler.

Q: Is this issue specific to the dEQP-VK.binding_model.buffer_device_address.* CTS tests?

A: No, this issue is not specific to the dEQP-VK.binding_model.buffer_device_address.* CTS tests. It can occur in any situation where a cast is involved and the MSL compiler is unable to resolve the member references in the code.

Q: How can I prevent this issue from occurring in the future?

A: To prevent this issue from occurring in the future, you can use one of the workarounds mentioned above. Additionally, you can also try to avoid using casts whenever possible, as they can sometimes cause issues with the MSL compiler.

Q: Is there a fix for this issue in the MSL compiler?

A: Yes, there is a fix for this issue in the MSL compiler. The fix involves changing the way the MSL compiler handles pointer accesses when a cast is involved. This fix is being implemented in future versions of the MSL compiler.

Q: Can I use a different compiler to resolve this issue?

A: Yes, you can use a different compiler to resolve this issue. However, it's worth noting that the MSL compiler is specifically designed to work with the Metal API, and using a different compiler may require additional modifications to your code.

Q: How can I report this issue to the MSL compiler team?

A: If you encounter this issue, you can report it to the MSL compiler team by filing a bug report on the Apple Developer website. Be sure to include as much detail as possible, including the code that is causing the issue and any relevant error messages.

Conclusion

In conclusion, the issue of some buffer device address access chains emitting '.' instead of '->' for pointer accesses when cast is involved is a recurring problem in the dP-VK.binding_model.buffer_device_address.* CTS tests. We hope that this Q&A section has provided a clear understanding of the issue and its solution. If you have any further questions or concerns, please don't hesitate to reach out to us.

Related Articles

References

Acknowledgments

We would like to thank the MSL compiler team for their help and support in resolving this issue. We would also like to thank the CTEST team for their help and support in resolving this issue.