[llvm] [VPlan] Add initial CFG simplification, removing BranchOnCond true. (PR #106748)

[Florian Hahn via llvm-commits]

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@@ -2817,6 +2817,7 @@ BasicBlock *InnerLoopVectorizer::createVectorizedLoopSkeleton(
   // faster.
   emitMemRuntimeChecks(LoopScalarPreHeader);
 
+  replaceVPBBWithIRVPBB(Plan.getScalarPreheader(), LoopScalarPreHeader);
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fhahn wrote:

At the original points, the scalar PH may be unreachable, which means at the moment we cannot use `getPlan()` . Calling it later ensures it will be connected, for now. 

Could independently improve this, by either storing parent plan in all VPBBs (not just the entries) or passing Plan to `replaceVPBBWithIRVPBB`

https://github.com/llvm/llvm-project/pull/106748