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

[via llvm-commits]

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@@ -456,21 +379,16 @@ void PlainCFGBuilder::buildPlainCFG(
   // corresponding VPlan operands.
   fixHeaderPhis();
 
-  VPBlockUtils::connectBlocks(Plan.getEntry(),
-                              getOrCreateVPBB(TheLoop->getHeader()));
+  Plan.getEntry()->setOneSuccessor(getOrCreateVPBB(TheLoop->getHeader()));
+  Plan.getEntry()->setPlan(&Plan);
 
   for (const auto &[IRBB, VPB] : BB2VPBB)
     VPB2IRBB[VPB] = IRBB;
+
+  LLVM_DEBUG(Plan.setName("Plain CFG\n"); dbgs() << Plan);
 }
 
 void VPlanHCFGBuilder::buildPlainCFG() {
   PlainCFGBuilder PCFGBuilder(TheLoop, LI, Plan);
   PCFGBuilder.buildPlainCFG(VPB2IRBB);
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ayalz wrote:

Seems even more redundant now to have both VPlanHCFGBuilder and PCFGBuilder, both with their buildPlainCFG().

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