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

[via llvm-commits]

https://github.com/ayalz approved this pull request.

This looks good to me, thanks.

Would be good to confirm the changes to two tests in llvm/test/Transforms/PhaseOrdering/AArch64/hoist-runtime-checks.ll are as desired.

Many test changes are due to sinking middle-block's compare down to its branch, occasionally beyond the coverage of CHECKs.

Leaving various minor comments.

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