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

[via llvm-commits]

ayalz wrote:

Nice step forward expanding VPlan's scope! Preliminary comments before diving in:

Commit message needs updating.

In general, VPlan backpatches branches when reaching their destination VPBB::execute() and VPBB::createEmptyBasicBlock(). This includes backpatching the branch leaving the vector loop when reaching its destination middle/exit VPBB. Could the branch ending middle block be backpatched similarly, when reaching its destination VPBB's - during VPIRBB::execute()?

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