Optimizations for index_select_scalar_cumsum_kernel on ROCm

[amd-wsung102]

This PR optimizes the performance of index_select_scalar_cumsum_kernel on ROCm using the following strategies.

• Implements vectorized gather and store by processing 4, 2, or 1 indices per thread based on indices length, improving memory coalescing and bandwidth.
• Uses a fast path for single-block workloads, which uses a simple block scan and early return.
• Uses a shared block prefix for multi-block cumulative sum.

There are code changes in 2 files:

• keyed_jagged_index_select_dim1.cu
• inclusive_sum_scan.cuh

ROCm-specific changes are guarded with #ifdef USE_ROCM.

[meta-cla]

Hi @amd-wsung102!

Thank you for your pull request and welcome to our community.

Action Required

In order to merge any pull request (code, docs, etc.), we require contributors to sign our Contributor License Agreement, and we don't seem to have one on file for you.

Process

In order for us to review and merge your suggested changes, please sign at https://code.facebook.com/cla. If you are contributing on behalf of someone else (eg your employer), the individual CLA may not be sufficient and your employer may need to sign the corporate CLA.

Once the CLA is signed, our tooling will perform checks and validations. Afterwards, the pull request will be tagged with CLA signed. The tagging process may take up to 1 hour after signing. Please give it that time before contacting us about it.

If you have received this in error or have any questions, please contact us at cla@meta.com. Thanks!

[meta-cla]

Thank you for signing our Contributor License Agreement. We can now accept your code for this (and any) Meta Open Source project. Thanks!

[meta-codesync]

@q10 has imported this pull request. If you are a Meta employee, you can view this in D89525621.