[llvm-dev] LLVM GPU News Issue #3, January 8 2021

Fri Jan 8 09:00:35 PST 2021

Hi folks,

The third issue of LLVM GPU News, a bi-weekly newsletter on all the GPU
things under the LLVM umbrella, is now available at:
https://llvm-gpu-news.github.io/2021/01/08/issue-3.html

I'm also pasting the content below, in case you prefer to read in your
email client.

-Jakub

======================================================================

# LLVM GPU News Issue #3, January 8 2021

Happy New Year! Welcome to the third issue of LLVM GPU News, a bi-weekly
newsletter on all the GPU things under the LLVM umbrella. This issue
covers the period from December 25 to January 7 2020.

We welcome your feedback and suggestions. Let us know if we missed anything
interesting, or want us to bring attention to your (sub)project, revisions
under review, or proposals. Please see the bottom of the page for details
on how to submit suggestions and contribute.

## Industry News and Conference Talks

*  Alyssa Rosenzweig started a blog post series on [dissecting the Apple
   M1 GPU](https://rosenzweig.io/blog/asahi-gpu-part-1.html), which
   doesn't have any public documentation or open source drivers as of
   writing. The goal is to understand the new architecture and accelerate
   the development of an open source driver stack. Alyssa already
   committed an [early work-in-progress disassembler
   implementation](
https://github.com/AsahiLinux/gpu/commit/35f700753635b45b743bd2e615c1801cbf982841
)
   and described the methodology and wokflow used to develop it in the
   blog post.

##  LLVM and Clang

### Discussions

*  Madhur Amilkanthwar asked about [using the Attributor framework to
   propagate the `amdgpu-flat-work-group-size` attribute in the AMDGPU
   backend](
https://lists.llvm.org/pipermail/llvm-dev/2021-January/147584.html).

### Commits

*  (In-review) [Remove a custom `amdgpu-inline` pass and replace it with
   new Target Transform Info hooks.](https://reviews.llvm.org/D94153)
   As explained, this is because the custom inliner doesn't fit well into
   the New Pass Manager's pipeline and has few differences compared to the
   main LLVM inlining pass.
*  [Clang won't add debugging information to NVPTX target if optimization
   remarks are enabled.](https://reviews.llvm.org/D94123) This is because
   `ptxas` supports either debug builds with no optimizations or
   optimized builds without debug info.
*  [Always print error messages in the `libomptarget` CUDA
   plugin](https://reviews.llvm.org/D94263), even with debugging
   disabled.
*  Make the [AMDGPU OpenMP target call into `deviceRTL` instead of
   `ockl`](https://reviews.llvm.org/D93356).
   This allows simple OpenMP code to run without ROCm device libraries
   installed.

## MLIR

### Discussions

*  Lenny Guo asked for [help with generating SPIR-V binaries from the
   SPIR-V MLIR dialect kernels](
https://llvm.discourse.group/t/generate-spirv-binary-from-mlir-dialect-kernels-to-run-it-on-ocl-runtime/2501
)
   in order to run them with OpenCL runtime. There are no replies as of
   writing.

### Commits

## External Compilers

Please submit pointers to your mailing lists, forums, or newsletters if you
want your LLVM- or MLIR-based GPU compiler project to be covered in future
LLVM GPU News issues.

### JuliaGPU

### LLPC

*  The graphics API-agnostic LGC peephole optimizer learned to
   [fold `inttoptr ( add x, const )` into
   `gep ( inttoptr x, const )`](
https://github.com/GPUOpen-Drivers/llpc/pull/1091).
   This improves value tracking and facilitates load/store vectorization.
   LLVM's instruction combining pass cannot generally perform the same
   optimization, because on some systems `const` itself may be a valid
   pointer.

### Mesa

*  [Always split typed vertex buffer loads on AMD GFX6 and GFX10+](
https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7751)
   in RADV/LLVM. This fixes hangs in [Zink](
https://docs.mesa3d.org/drivers/zink.html)
   (an OpenGL over Vulkan implementation) tests.

### SYCL
*  [Intel's oneAPI DPC++ Compiler 2020-12 got released.](
https://github.com/intel/llvm/releases/tag/2020-12)
   The release notes contain a long list of SYCL compiler and library
   improvements.

-- 
Jakub Kuderski
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