[llvm] [VPlan] Refactor VPlan creation, add transform introducing region (NFC). (PR #128419)

[via llvm-commits]

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@@ -449,16 +427,22 @@ void PlainCFGBuilder::buildPlainCFG(
     VPBasicBlock *Successor0 = getOrCreateVPBB(IRSucc0);
     VPBasicBlock *Successor1 = getOrCreateVPBB(IRSucc1);
     if (BB == LoopForBB->getLoopLatch()) {
-      // For a latch we need to set the successor of the region rather than that
-      // of VPBB and it should be set to the exit, i.e., non-header successor,
+      // For a latch we need to set the successor of the region rather
+      // than that
+      // of VPBB and it should be set to the exit, i.e., non-header
+      // successor,
       // except for the top region, whose successor was set when creating
       // VPlan's skeleton.
-      assert(TheRegion != Region &&
+      assert(LoopForBB != TheLoop &&
              "Latch of the top region should have been handled earlier");
       Region->setOneSuccessor(isHeaderVPBB(Successor0) ? Successor1
                                                        : Successor0);
       Region->setExiting(VPBB);
       continue;
+
+      VPBasicBlock *HeaderVPBB = getOrCreateVPBB(LoopForBB->getHeader());
+      VPBlockUtils::connectBlocks(VPBB, HeaderVPBB);
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ayalz wrote:

Can be folded with handling TheLoop's latch above, with an early continue if LoopForBB == TheLoop.

https://github.com/llvm/llvm-project/pull/128419