[llvm] [LV] Always try to use fixed VF for low TC loops if no epilogue allowed. (PR #226318)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `lldb-aarch64-ubuntu` running on `arm-bbot-lldb-aarch64-ubuntu` while building `llvm` at step 6 "test".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/59/builds/37977

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test) failure: build (failure)
...
PASS: lldb-api :: commands/version/TestVersion.py (296 of 2690)
PASS: lldb-api :: commands/settings/TestSettings.py (297 of 2690)
PASS: lldb-api :: commands/settings/quoting/TestQuoting.py (298 of 2690)
PASS: lldb-api :: commands/watchpoints/multi_watchpoint_slots/TestWatchpointMultipleSlots.py (299 of 2690)
SKIPPED: lldb-api :: commands/watchpoints/multiple_hits/TestMultipleHits.py (300 of 2690)
PASS: lldb-api :: commands/watchpoints/unaligned-watchpoint/TestUnalignedWatchpoint.py (301 of 2690)
SKIPPED: lldb-api :: commands/watchpoints/variable_out_of_scope/TestWatchedVarHitWhenInScope.py (302 of 2690)
PASS: lldb-api :: commands/watchpoints/watchpoint_commands/condition/TestWatchpointConditionCmd.py (303 of 2690)
SKIPPED: lldb-api :: commands/watchpoints/watchpoint_count/TestWatchpointCount.py (304 of 2690)
UNRESOLVED: lldb-api :: api/multithreaded/TestMultithreaded.py (305 of 2690)
******************** TEST 'lldb-api :: api/multithreaded/TestMultithreaded.py' FAILED ********************
Script:
--
/usr/bin/python3.12 /home/buildbot/workspace/lldb-aarch64-ubuntu/llvm-project/lldb/test/API/dotest.py -u CXXFLAGS -u CFLAGS --env LLVM_LIBS_DIR=/home/buildbot/workspace/lldb-aarch64-ubuntu/build/./lib --env LLVM_INCLUDE_DIR=/home/buildbot/workspace/lldb-aarch64-ubuntu/build/include --env LLVM_TOOLS_DIR=/home/buildbot/workspace/lldb-aarch64-ubuntu/build/./bin --triple aarch64-unknown-linux-gnu --build-dir /home/buildbot/workspace/lldb-aarch64-ubuntu/build/lldb-test-build --lldb-module-cache-dir /home/buildbot/workspace/lldb-aarch64-ubuntu/build/lldb-test-build/module-cache-lldb/lldb-api --clang-module-cache-dir /home/buildbot/workspace/lldb-aarch64-ubuntu/build/lldb-test-build/module-cache-clang/lldb-api --executable /home/buildbot/workspace/lldb-aarch64-ubuntu/build/./bin/lldb --lldb-python-dir /home/buildbot/workspace/lldb-aarch64-ubuntu/build/local/lib/python3.12/dist-packages --compiler /home/buildbot/workspace/lldb-aarch64-ubuntu/build/./bin/clang --dsymutil /home/buildbot/workspace/lldb-aarch64-ubuntu/build/./bin/dsymutil --make /usr/bin/gmake --llvm-tools-dir /home/buildbot/workspace/lldb-aarch64-ubuntu/build/./bin --lldb-obj-root /home/buildbot/workspace/lldb-aarch64-ubuntu/build/tools/lldb --lldb-libs-dir /home/buildbot/workspace/lldb-aarch64-ubuntu/build/./lib --cmake-build-type Release /home/buildbot/workspace/lldb-aarch64-ubuntu/llvm-project/lldb/test/API/api/multithreaded -p TestMultithreaded.py --timeout 600
--
Exit Code: 1

Command Output (stdout):
--
Adding command some-cmd and report-cmd
some output
(lldb) thread step-inst
check_state: running  OK
check_state: stopped  OK
Skipping the following test categories: libc++, msvcstl, dsym, pdb, gmodules, debugserver, objc

--
Command Output (stderr):
--
PASS: LLDB (/home/buildbot/workspace/lldb-aarch64-ubuntu/build/bin/clang-aarch64) :: test_breakpoint_callback (TestMultithreaded.SBBreakpointCallbackCase.test_breakpoint_callback)
PASS: LLDB (/home/buildbot/workspace/lldb-aarch64-ubuntu/build/bin/clang-aarch64) :: test_breakpoint_location_callback (TestMultithreaded.SBBreakpointCallbackCase.test_breakpoint_location_callback)
PASS: LLDB (/home/buildbot/workspace/lldb-aarch64-ubuntu/build/bin/clang-aarch64) :: test_concurrent_unwind (TestMultithreaded.SBBreakpointCallbackCase.test_concurrent_unwind)
test_python_stop_hook: /home/buildbot/workspace/lldb-aarch64-ubuntu/llvm-project/lldb/source/Target/ThreadPlanStack.cpp:153: lldb::ThreadPlanSP lldb_private::ThreadPlanStack::PopPlan(): Assertion `m_plans.size() > 1 && "Can't pop the base thread plan"' failed.
FAIL: LLDB (/home/buildbot/workspace/lldb-aarch64-ubuntu/build/bin/clang-aarch64) :: test_python_stop_hook (TestMultithreaded.SBBreakpointCallbackCase.test_python_stop_hook)
Log Files:
 - /home/buildbot/workspace/lldb-aarch64-ubuntu/build/lldb-test-build/api/multithreaded/TestMultithreaded.test_python_stop_hook/Error_test_python_stop_hook.log
PASS: LLDB (/home/buildbot/workspace/lldb-aarch64-ubuntu/build/bin/clang-aarch64) :: test_sb_api_listener_event_description (TestMultithreaded.SBBreakpointCallbackCase.test_sb_api_listener_event_description)
PASS: LLDB (/home/buildbot/workspace/lldb-aarch64-ubuntu/build/bin/clang-aarch64) :: test_sb_api_listener_event_process_state (TestMultithreaded.SBBreakpointCallbackCase.test_sb_api_listener_event_process_state)
SKIPPED: LLDB (/home/buildbot/workspace/lldb-aarch64-ubuntu/build/bin/clang-aarch64) :: test_sb_api_listener_resume (TestMultithreaded.SBBreakpointCallbackCase.test_sb_api_listener_resume) (skipping due to the following parameter(s): target o/s) 
Log Files:
 - /home/buildbot/workspace/lldb-aarch64-ubuntu/build/lldb-test-build/api/multithreaded/TestMultithreaded.test_sb_api_listener_resume/SkippedTest_test_sb_api_listener_resume.log
======================================================================
ERROR: test_python_stop_hook (TestMultithreaded.SBBreakpointCallbackCase.test_python_stop_hook)
   Test that you can run a python command in a stop-hook when stdin is File based.
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/buildbot/workspace/lldb-aarch64-ubuntu/llvm-project/lldb/packages/Python/lldbsuite/test/decorators.py", line 221, in wrapper
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^

```

</details>

https://github.com/llvm/llvm-project/pull/226318