[Fix] Avoid generating dangling free var ceil_log2 for gpu_generic backends

[akaashrp]

The unused variable ceil_log2 was causing downstream errors in MLC-LLM during compilation for metal and webgpu. This PR removes this intermediate variable and moves it to the total_rounds calculation.

[gemini-code-assist]

Summary of Changes

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This pull request refines the code within the gpu_generic backend for the cumsum operation. The primary goal is to prevent the generation of an unnecessary intermediate variable, which could lead to a "dangling free variable" issue during code compilation for GPU targets. By streamlining the calculation, the change contributes to cleaner and potentially more robust generated code.

Highlights

• Code Refinement: Eliminated the intermediate variable "ceil_log2" in the "cumsum" function within "gpu_generic" backends, directly integrating its calculation into "total_rounds" to prevent the generation of a dangling free variable.

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Changelog

• python/tvm/relax/backend/gpu_generic/cumsum.py
  • Removed an intermediate variable ceil_log2 and inlined its calculation.

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Code Review

This pull request addresses a bug in the gpu_generic cumsum implementation where an intermediate variable ceil_log2 was causing issues, as described in the title. The fix involves inlining the expression for ceil_log2 directly into the calculation of total_rounds. This change correctly resolves the issue by removing the temporary variable. The resulting code is more concise and functionally correct.