llvm-project

6aa115bb - Reapply "[VPlan] Remove manual region removal when simplifying for VF and UF. (#181252)"

Reapply "[VPlan] Remove manual region removal when simplifying for VF and UF. (#181252)" This reverts commit d7e037c8383e66e5c07897f144f6d8ef47258682. Recommit with a small fix to properly handle ordered reductions when connecting the epilogue. Original message: Replace manual region dissolution code in simplifyBranchConditionForVFAndUF with using general removeBranchOnConst. simplifyBranchConditionForVFAndUF now just creates a (BranchOnCond true) or updates BranchOnTwoConds. The loop then gets automatically removed by running removeBranchOnConst. This removes a bunch of special logic to handle header phi replacements and CFG updates. With the new code, there's no restriction on what kind of header phi recipes the loop contains. Note that VPEVLBasedIVRecipe needs to be marked as readnone. This is technically unrelated, but I could not find an independent test that would be impacted. The code to deal with epilogue resume values now needs updating, because we may simplify a reduction directly to the start value. PR: https://github.com/llvm/llvm-project/pull/181252