[llvm] [LV] Add coverage for fixing-up scalar resume values (PR #160492)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-aarch64-darwin` running on `doug-worker-5` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/190/builds/28178

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

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM :: Transforms/LoopVectorize/AArch64/epilogue-vectorization-fix-scalar-resume-values.ll' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 2
/Volumes/ExternalSSD/buildbot-root/aarch64-darwin/build/bin/opt -passes=loop-vectorize -S /Users/buildbot/buildbot-root2/aarch64-darwin/llvm-project/llvm/test/Transforms/LoopVectorize/AArch64/epilogue-vectorization-fix-scalar-resume-values.ll | /Volumes/ExternalSSD/buildbot-root/aarch64-darwin/build/bin/FileCheck /Users/buildbot/buildbot-root2/aarch64-darwin/llvm-project/llvm/test/Transforms/LoopVectorize/AArch64/epilogue-vectorization-fix-scalar-resume-values.ll
# executed command: /Volumes/ExternalSSD/buildbot-root/aarch64-darwin/build/bin/opt -passes=loop-vectorize -S /Users/buildbot/buildbot-root2/aarch64-darwin/llvm-project/llvm/test/Transforms/LoopVectorize/AArch64/epilogue-vectorization-fix-scalar-resume-values.ll
# note: command had no output on stdout or stderr
# executed command: /Volumes/ExternalSSD/buildbot-root/aarch64-darwin/build/bin/FileCheck /Users/buildbot/buildbot-root2/aarch64-darwin/llvm-project/llvm/test/Transforms/LoopVectorize/AArch64/epilogue-vectorization-fix-scalar-resume-values.ll
# .---command stderr------------
# | /Users/buildbot/buildbot-root2/aarch64-darwin/llvm-project/llvm/test/Transforms/LoopVectorize/AArch64/epilogue-vectorization-fix-scalar-resume-values.ll:33:15: error: CHECK-NEXT: expected string not found in input
# | ; CHECK-NEXT: [[N_VEC_REMAINING:%.*]] = sub i64 [[REM]], [[N_VEC]]
# |               ^
# | <stdin>:33:23: note: scanning from here
# | vec.epilog.iter.check: ; preds = %middle.block
# |                       ^
# | <stdin>:33:23: note: with "REM" equal to "%rem"
# | vec.epilog.iter.check: ; preds = %middle.block
# |                       ^
# | <stdin>:33:23: note: with "N_VEC" equal to "%n.vec"
# | vec.epilog.iter.check: ; preds = %middle.block
# |                       ^
# | <stdin>:38:19: note: possible intended match here
# |  %vec.epilog.resume.val = phi i64 [ %n.vec, %vec.epilog.iter.check ], [ 0, %vector.main.loop.iter.check ]
# |                   ^
# | 
# | Input file: <stdin>
# | Check file: /Users/buildbot/buildbot-root2/aarch64-darwin/llvm-project/llvm/test/Transforms/LoopVectorize/AArch64/epilogue-vectorization-fix-scalar-resume-values.ll
# | 
# | -dump-input=help explains the following input dump.
# | 
# | Input was:
# | <<<<<<
# |             1: ; ModuleID = '/Users/buildbot/buildbot-root2/aarch64-darwin/llvm-project/llvm/test/Transforms/LoopVectorize/AArch64/epilogue-vectorization-fix-scalar-resume-values.ll' 
# |             2: source_filename = "/Users/buildbot/buildbot-root2/aarch64-darwin/llvm-project/llvm/test/Transforms/LoopVectorize/AArch64/epilogue-vectorization-fix-scalar-resume-values.ll" 
# |             3: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128-Fn32" 
# |             4: target triple = "aarch64" 
# |             5:  
# |             6: define void @epilogue_vectorization_fix_scalar_resume_values(ptr %dst, i64 %n) { 
# | label:9'0      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# | label:9'1      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# | same:10'0                                                                   ^~~~~~~~~~~~~~~~~~~
# | same:10'1                                                                       ^~~~             captured var "DST"
# | same:10'2                                                                                 ^~     captured var "N"
# |             7: iter.check: 
# | next:11'0      ^~~~~~~~~~~
# | next:11'1      ^~~~~~~~~~   captured var "ITER_CHECK"
# |             8:  %rem = urem i64 %n, 3 
# | next:12'0       ^~~~~~~~~~~~~~~~~~~~~
...

```

</details>

https://github.com/llvm/llvm-project/pull/160492