[llvm] [VPlan] Model branch cond to enter scalar epilogue in VPlan. (PR #92651)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-expensive-checks-debian` running on `gribozavr4` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/16/builds/1270

Here is the relevant piece of the build log for the reference:
```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM :: Analysis/CostModel/X86/gather-i16-with-i8-index.ll' FAILED ********************
Exit Code: 134

Command Output (stderr):
--
RUN: at line 2: /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/opt -passes=loop-vectorize -vectorizer-maximize-bandwidth -S -mattr=+sse2 --debug-only=loop-vectorize < /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/Analysis/CostModel/X86/gather-i16-with-i8-index.ll 2>&1 | /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/FileCheck /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/Analysis/CostModel/X86/gather-i16-with-i8-index.ll --check-prefixes=SSE
+ /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/FileCheck /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/Analysis/CostModel/X86/gather-i16-with-i8-index.ll --check-prefixes=SSE
+ /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/opt -passes=loop-vectorize -vectorizer-maximize-bandwidth -S -mattr=+sse2 --debug-only=loop-vectorize
RUN: at line 3: /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/opt -passes=loop-vectorize -vectorizer-maximize-bandwidth -S -mattr=+sse4.2 --debug-only=loop-vectorize < /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/Analysis/CostModel/X86/gather-i16-with-i8-index.ll 2>&1 | /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/FileCheck /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/Analysis/CostModel/X86/gather-i16-with-i8-index.ll --check-prefixes=SSE
+ /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/FileCheck /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/Analysis/CostModel/X86/gather-i16-with-i8-index.ll --check-prefixes=SSE
+ /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/opt -passes=loop-vectorize -vectorizer-maximize-bandwidth -S -mattr=+sse4.2 --debug-only=loop-vectorize
RUN: at line 4: /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/opt -passes=loop-vectorize -vectorizer-maximize-bandwidth -S -mattr=+avx  --debug-only=loop-vectorize < /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/Analysis/CostModel/X86/gather-i16-with-i8-index.ll 2>&1 | /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/FileCheck /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/Analysis/CostModel/X86/gather-i16-with-i8-index.ll --check-prefixes=AVX1
+ /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/opt -passes=loop-vectorize -vectorizer-maximize-bandwidth -S -mattr=+avx --debug-only=loop-vectorize
+ /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/FileCheck /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/Analysis/CostModel/X86/gather-i16-with-i8-index.ll --check-prefixes=AVX1
RUN: at line 5: /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/opt -passes=loop-vectorize -vectorizer-maximize-bandwidth -S -mattr=+avx2,-fast-gather --debug-only=loop-vectorize < /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/Analysis/CostModel/X86/gather-i16-with-i8-index.ll 2>&1 | /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/FileCheck /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/Analysis/CostModel/X86/gather-i16-with-i8-index.ll --check-prefixes=AVX2-SLOWGATHER
+ /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/opt -passes=loop-vectorize -vectorizer-maximize-bandwidth -S -mattr=+avx2,-fast-gather --debug-only=loop-vectorize
+ /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/FileCheck /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/Analysis/CostModel/X86/gather-i16-with-i8-index.ll --check-prefixes=AVX2-SLOWGATHER
/b/1/llvm-clang-x86_64-expensive-checks-debian/build/test/Analysis/CostModel/X86/Output/gather-i16-with-i8-index.ll.script: line 6: 618816 Aborted                 /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/opt -passes=loop-vectorize -vectorizer-maximize-bandwidth -S -mattr=+avx2,-fast-gather --debug-only=loop-vectorize < /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/Analysis/CostModel/X86/gather-i16-with-i8-index.ll 2>&1
     618818 Done                    | /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/FileCheck /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/Analysis/CostModel/X86/gather-i16-with-i8-index.ll --check-prefixes=AVX2-SLOWGATHER

--

********************


```

https://github.com/llvm/llvm-project/pull/92651