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

[David Sherwood via llvm-commits]

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@@ -2658,7 +2659,9 @@ void InnerLoopVectorizer::createVectorLoopSkeleton(StringRef Prefix) {
   LoopScalarPreHeader =
       SplitBlock(LoopVectorPreHeader, LoopVectorPreHeader->getTerminator(), DT,
                  LI, nullptr, Twine(Prefix) + "scalar.ph");
-  replaceVPBBWithIRVPBB(Plan.getScalarPreheader(), LoopScalarPreHeader);
+  // NOTE: The Plan's scalar preheader isn't replaced with a VPIRBasicBlock
+  // wrapping LoopScalarPreHeader here at the moment, because the Plan's scalar
+  // preheader may be unreachable at this point.
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david-arm wrote:

Is it worth helping the reader by pointing to the place where we do replace it, i.e. `createVectorizedLoopSkeleton`?

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