Minor perf improvements to quantized mat mul shader.

[trivedivivek]

Summary: The diff includes minor performance improvements to the quantized matrix multiplication shader.

Differential Revision: D84998542

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/15261

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

❗ 1 Active SEVs

There are 1 currently active SEVs. If your PR is affected, please view them below:

• AWS was down, GHA infrastructure effected / recovering

❌ 9 New Failures, 2 Unrelated Failures

As of commit 196de84 with merge base 0a1dfb2 ():

NEW FAILURES - The following jobs have failed:

• pull / android / run-emulator (gh)
  The process '/usr/bin/sh' failed with exit code 255
• pull / test-samsung-models-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 40a46bfeeb9866ae54cc04ea612b2d938761eb2d2f214173bdf9067bb09cfaa4 /exec failed with exit code 1
• pull / unittest / macos / macos-job (gh)
  export/tests/test_target_recipes.py::TestTargetRecipes::test_linear_model
• pull / unittest-arm-backend-with-no-fvp (test_pytest_models) / linux-job (gh)
  RuntimeError: Command docker exec -t 8bc049e1867f096f0ac2649fcb06a83fa54f9fe50bf53b6e57c5da78f0face93 /exec failed with exit code 1
• pull / unittest-nxp-neutron / linux-job (gh)
  RuntimeError: Command docker exec -t 46e0e03b4a49483ee48579d744e1079daeb5b3951316968d58dffca23daa0e19 /exec failed with exit code 1
• Test CUDA Builds / export-voxtral-cuda-non-quantized / linux-job (gh)
  RuntimeError: Command docker exec -t 3ea321a9a28b9486b9041ea20a27563a5b3a35e67fb6869dee9801ebff2da09b /exec failed with exit code 2
• Test CUDA Builds / export-voxtral-cuda-quantized-int4-tile-packed / linux-job (gh)
  RuntimeError: Command docker exec -t fbb919e47c7cc42be3a11e7790bb1b8a2c8aac60094413e0d33da6e2fadfe521 /exec failed with exit code 2
• Test CUDA Builds / export-voxtral-cuda-quantized-int4-weight-only / linux-job (gh)
  RuntimeError: Command docker exec -t 2cd9fa177518772234bf198d06d9d648c26bf11e76dcf4b7741c41c782b1d7ab /exec failed with exit code 2
• Test Metal Backend / export-voxtral-metal-artifact / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 2

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• pull / unittest / linux / linux-job (gh) (matched linux rule in flaky-rules.json)
  The runner has received a shutdown signal. This can happen when the runner service is stopped, or a manually started runner is canceled.

BROKEN TRUNK - The following job failed but was present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / unittest-editable / linux / linux-job (gh) (trunk failure)

This comment was automatically generated by Dr. CI and updates every 15 minutes.

[meta-codesync]

@trivedivivek has exported this pull request. If you are a Meta employee, you can view the originating Diff in D84998542.