[https://nvbugs/5829830][fix] Declare the var in the correct scope

[ziyixiong-nv]

Summary by CodeRabbit

• Refactor
  • Optimized memory synchronization and buffer management in compute kernel execution paths for improved efficiency.

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Description

The change is required because of https://github.com/NVIDIA/TensorRT-LLM/blob/main/cpp/kernels/xqa/mha_sm90.cu#L1419 .

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[ziyixiong-nv]

/bot run

[coderabbitai]

📝 Walkthrough

Walkthrough

Modified conditional compilation logic in the MHA CUDA kernel to conditionally include VT (vital V) buffers and synchronization barriers when SWAP_AB is not defined, while removing their usage from the XVGemm path in non-SWAP_AB branches to align synchronization strategies.

Changes

Cohort / File(s)	Summary
MHA kernel synchronization refactoring cpp/kernels/xqa/mha_sm90.cu	Added conditional guards (#if !SWAP_AB) around VT buffer and barrier declarations (vtBar, vtBuf) to control their inclusion based on compilation flags. Removed corresponding VT-related barrier/buffer usage from XVGemm execution paths in non-SWAP_AB branch to maintain coherent synchronization strategy across conditional pathways.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

🚥 Pre-merge checks | ✅ 1 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.
Description check	⚠️ Warning	PR description is incomplete with missing key information sections.	Add a clear explanation of the issue and solution in the Description section, and list the test cases that validate these changes in the Test Coverage section.

✅ Passed checks (1 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main fix: moving variable declarations to the correct scope, which aligns with the code changes that conditionally declare VT buffers and barriers based on preprocessor definitions.

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[tensorrt-cicd]

PR_Github #33881 [ run ] triggered by Bot. Commit: 16ef556

[mikeiovine]

Do any tests need to be unwaived? Also, I think we need to merge the fix to release/1.2

[tensorrt-cicd]

PR_Github #33881 [ run ] completed with state SUCCESS. Commit: 16ef556
/LLM/main/L0_MergeRequest_PR pipeline #26127 completed with status: 'FAILURE'

⚠️ Action Required:

• Please check the failed tests and fix your PR
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[ziyixiong-nv]

Do any tests need to be unwaived? Also, I think we need to merge the fix to release/1.2

Retargeted it to release/1.2. The test is not in waive list, so we don't need to unwaive anything.

[ziyixiong-nv]

/bot run

[tensorrt-cicd]

PR_Github #33938 [ run ] triggered by Bot. Commit: e8c293d

[tensorrt-cicd]

PR_Github #33938 [ run ] completed with state SUCCESS. Commit: e8c293d
/LLM/release-1.2/L0_MergeRequest_PR pipeline #262 completed with status: 'SUCCESS'

[ziyixiong-nv]

/bot run --reuse-pipeline

[tensorrt-cicd]

PR_Github #34139 Bot args parsing error: usage: /bot [-h]
{run,kill,skip,submit,reviewers,reuse-pipeline,reuse-review} ...
/bot: error: unrecognized arguments: --reuse-pipeline

[ziyixiong-nv]

/bot reuse-pipeline

[tensorrt-cicd]

PR_Github #34145 [ reuse-pipeline ] triggered by Bot. Commit: b078e62

[tensorrt-cicd]

PR_Github #34145 [ reuse-pipeline ] completed with state SUCCESS. Commit: b078e62
Reusing PR_Github #33938 for commit b078e62