[llvm] [VPlan] Add VPlan-dump-based test for predication (PR #180794)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-sie-ubuntu-fast` running on `sie-linux-worker` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/144/builds/46923

<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/VPlan/predicator.ll' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 2
/home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/opt -disable-output < /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/llvm/test/Transforms/LoopVectorize/VPlan/predicator.ll -p loop-vectorize -vplan-print-after=introduceMasksAndLinearize -vplan-print-vector-region-scope 2>&1 | /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/FileCheck /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/llvm/test/Transforms/LoopVectorize/VPlan/predicator.ll
# executed command: /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/opt -disable-output -p loop-vectorize -vplan-print-after=introduceMasksAndLinearize -vplan-print-vector-region-scope
# note: command had no output on stdout or stderr
# executed command: /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/FileCheck /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/llvm/test/Transforms/LoopVectorize/VPlan/predicator.ll
# .---command stderr------------
# | /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/llvm/test/Transforms/LoopVectorize/VPlan/predicator.ll:101:15: error: CHECK-NEXT: expected string not found in input
# | ; CHECK-NEXT: BLEND ir<%phi4> = ir<%add3>/vp<[[VP7]]> ir<%add0>/vp<[[VP8]]>
# |               ^
# | <stdin>:60:33: note: scanning from here
# |  EMIT vp<%9> = or vp<%7>, vp<%8>
# |                                 ^
# | <stdin>:60:33: note: with "VP7" equal to "%7"
# |  EMIT vp<%9> = or vp<%7>, vp<%8>
# |                                 ^
# | <stdin>:60:33: note: with "VP8" equal to "%8"
# |  EMIT vp<%9> = or vp<%7>, vp<%8>
# |                                 ^
# | <stdin>:61:2: note: possible intended match here
# |  BLEND ir<%phi4> = ir<%add3>/vp<%7> ir<%iv>/vp<%8>
# |  ^
# | 
# | Input file: <stdin>
# | Check file: /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/llvm/test/Transforms/LoopVectorize/VPlan/predicator.ll
# | 
# | -dump-input=help explains the following input dump.
# | 
# | Input was:
# | <<<<<<
# |              1: VPlan for loop in 'diamond_phi' after VPlanTransforms::introduceMasksAndLinearize 
# | label:5'0                         ^~~~~~~~~~~~~
# | label:5'1                         ^~~~~~~~~~~~~
# |              2: <x1> vector loop: { 
# | next:6          ^~~~~~~~~~~~~~~~~~~
# |              3:  vector.body: 
# | next:7           ^~~~~~~~~~~~
# |              4:  EMIT vp<%3> = CANONICAL-INDUCTION ir<0>, vp<%index.next> 
# | next:8'0         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# | next:8'1                 ^~                                                captured var "VP3"
# |              5:  ir<%iv> = WIDEN-INDUCTION nuw nsw ir<0>, ir<1>, vp<%0> 
# | next:9'0         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# | next:9'1                                                            ^~   captured var "VP0"
# |              6:  EMIT ir<%gep> = getelementptr ir<%a>, ir<%iv> 
# | next:10          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# |              7:  EMIT ir<%c0> = icmp sle ir<%iv>, ir<0> 
...

```

</details>

https://github.com/llvm/llvm-project/pull/180794