[llvm] [VPlan] Introduce child regions as VPlan transform. (PR #129402)

[via llvm-commits]

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@@ -113,13 +88,6 @@ static bool isHeaderBB(BasicBlock *BB, Loop *L) {
   return L && BB == L->getHeader();
 }
 
-void PlainCFGBuilder::setRegionPredsFromBB(VPRegionBlock *Region,
-                                           BasicBlock *BB) {
-  // BB is a loop header block. Connect the region to the loop preheader.
-  Loop *LoopOfBB = LI->getLoopFor(BB);
-  Region->setPredecessors({getOrCreateVPBB(LoopOfBB->getLoopPredecessor())});
-}
-
 // Add operands to VPInstructions representing phi nodes from the input IR.
 void PlainCFGBuilder::fixHeaderPhis() {
   for (auto *Phi : PhisToFix) {
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ayalz wrote:

Header phi's expect preheader as first predecessor and latch as second, corresponding to operands added below, so make sure here the predecessors are ordered accordingly, i.e., swap if needed? Later when loop regions are introduced, can rely on this order.

https://github.com/llvm/llvm-project/pull/129402