[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 `lld-x86_64-ubuntu-fast` running on `as-builder-4` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/33/builds/23692

<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
/home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/bin/opt -passes=loop-vectorize -S /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/Transforms/LoopVectorize/AArch64/epilogue-vectorization-fix-scalar-resume-values.ll | /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/bin/FileCheck /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/Transforms/LoopVectorize/AArch64/epilogue-vectorization-fix-scalar-resume-values.ll
# executed command: /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/bin/opt -passes=loop-vectorize -S /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/Transforms/LoopVectorize/AArch64/epilogue-vectorization-fix-scalar-resume-values.ll
# executed command: /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/bin/FileCheck /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/Transforms/LoopVectorize/AArch64/epilogue-vectorization-fix-scalar-resume-values.ll
# .---command stderr------------
# | /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/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: /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/Transforms/LoopVectorize/AArch64/epilogue-vectorization-fix-scalar-resume-values.ll
# | 
# | -dump-input=help explains the following input dump.
# | 
# | Input was:
# | <<<<<<
# |            .
# |            .
# |            .
# |           28:  
# |           29: middle.block: ; preds = %vector.body 
# |           30:  %cmp.n = icmp eq i64 %rem, %n.vec 
# |           31:  br i1 %cmp.n, label %exit, label %vec.epilog.iter.check 
# |           32:  
# |           33: vec.epilog.iter.check: ; preds = %middle.block 
# | next:33'0                           X~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
# | next:33'1                                                     with "REM" equal to "%rem"
# | next:33'2                                                     with "N_VEC" equal to "%n.vec"
# |           34:  %min.epilog.iters.check = icmp ult i64 %n.mod.vf, 8 
# | next:33'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# |           35:  br i1 %min.epilog.iters.check, label %vec.epilog.scalar.ph, label %vec.epilog.ph, !prof !3 
# | next:33'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# |           36:  
...

```

</details>

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