Create KV cache input tensor only if cache len > 0 for that layer

[sxu]

Differential Revision: D84471388

The MHA branch has this logic already, add it to the other branch.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/15042

• 📄 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:

• [ROCm][CI] Machines under the label linux.rocm.gpu.2 are undergoing maintenance.

❌ 6 New Failures, 4 Unrelated Failures

As of commit 6d3025d with merge base d00279d ():

NEW FAILURES - The following jobs have failed:

• Build Presets / apple (pybind) / build (gh)
  Library not loaded: @rpath/libzstd.1.dylib
• pull / test-qnn-wheel-packages-linux (3.10) / linux-job (gh)
  RuntimeError: Command docker exec -t 142e916c234274a90a7c159d2c0938cfe8b8df51c1195ade2f39ed9f4a2e95a1 /exec failed with exit code 1
• pull / test-qnn-wheel-packages-linux (3.11) / linux-job (gh)
  RuntimeError: Command docker exec -t 0e92cfef858e1ea8dc7ca36ff8d83a526a274b953c1c09c563e0dc1b34a8a5d9 /exec failed with exit code 1
• pull / test-qnn-wheel-packages-linux (3.12) / linux-job (gh)
  RuntimeError: Command docker exec -t d5e4713e36d3aff8edc937d86e65abbede6ce6afd18dd8727a153e5550e8dab2 /exec failed with exit code 1
• pull / test-samsung-models-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 8c659274d465ff40c484147beaacbf78d6cf528e4dba7432ce79e9d4df840e1b /exec failed with exit code 1
• Test CUDA Builds / export-voxtral-cuda-artifact / linux-job (gh)
  RuntimeError: Command docker exec -t 8b7ccc2c7c05a8417dbaee723e0f11691d49ea8554ba9717867887ab55064c2d /exec 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 jobs failed but was present on the merge base:

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

• pull / unittest / macos / macos-job (gh) (trunk failure)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1
• pull / unittest-buck / macos / macos-job (gh) (trunk failure)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1
• pull / unittest-editable / macos / macos-job (gh) (trunk failure)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1

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

[meta-codesync]

@sxu has exported this pull request. If you are a Meta employee, you can view the originating Diff in D84471388.