[GSoC 2026] DCompute Vulkan Backend

[Quang Ha]

Hi everyone, here is my progress update for **Week 1** of the 
DCompute Vulkan Backend project.

#### 🛠️ What I Did This Week
   * Squashed [Nicholas's 
PR](https://github.com/ldc-developers/ldc/pull/4958) to 
thoroughly analyze the required implementation details in 
`targetVulkan.cpp` and `dcomputecodegenerator.cpp`.

   * Investigated the `TODO` in `dcomputecodegenerator.cpp` and 
implemented support for parsing the `vulkan-{version}` target 
value by adapting the existing OpenCL (OCL) and CUDA logic.

   * Updated `cl_options.cpp` to include Vulkan in the 
`--mdcompute-targets` flag's description.

   * Addressed the hardcoded 64-bit pointer assignment in 
`targetVulkan.cpp` to fix the layout issue for different pointer 
sizes.

   * Refactored relevant files by updating the LLVM version macro 
checks from `LLVM_LDC_VER >= 2100` to `LLVM_VERSION_MAJOR >= 23`.

#### 🛑 Challenges
   * **The .spv file output problem:** I used the 
`--mdcompute-targets` flag to make a `.spv` file, but it was in 
COFF format, not real SPIR-V. It was very strange. When I added a 
logging line just to print things out, it made correct SPIR-V 
code. After that, I built the newest LLVM 23 (on May 24), and it 
went back to COFF format. Nicholas and I didn't understand why. 
Finally, I fixed it. I copied the "HACK" part from 
`DComputeTarget::emit` to `DComputeTarget::writeModule`. Now it 
works normally.

   * **Build error:** I got a linker error when building. But it 
was easy to fix. I just changed the paths in the `CMakeLists.txt` 
file.

   * **The TODO part:** There is a `TODO` for `spirv.Layout` in 
`targetVulkan.cpp`. It is very difficult to understand. So, I 
haven't touched it yet. I need more time to study it.

#### 🎯 Plans for Next Week
   * **Look into spirv.Layout:** I will spend time studying the 
`TODO` about `spirv.Layout` in `targetVulkan.cpp` because I 
didn't finish it this week.

   * **Write more tests:** I will write some more test files to 
make sure the compiler always makes the correct `.spv` files.

   * **Update my PR:** I will wait for Nicholas to finish 
reviewing my PR. Then, I will update the code and fix any issues 
he points out.

#### 🔗 Resources & Code
* Commits/PRs: https://github.com/ldc-developers/ldc/pull/5132
* My Personal Blog: Will update soon!

Feel free to leave any feedback or suggestions!