[VPlan] Move runtime check blocks to correct position during exec (NFC).

Move adjusting the position of completely disconnected IR blocks to
VPIRBasicBlock::execute.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -7268,8 +7268,6 @@ DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
 
   // 1. Set up the skeleton for vectorization, including vector pre-header and
   // middle block. The vector loop is created during VPlan execution.
-  BasicBlock *EntryBB =
-      cast<VPIRBasicBlock>(BestVPlan.getEntry())->getIRBasicBlock();
   State.CFG.PrevBB = ILV.createVectorizedLoopSkeleton();
   replaceVPBBWithIRVPBB(BestVPlan.getScalarPreheader(),
                         State.CFG.PrevBB->getSingleSuccessor());
@@ -7303,13 +7301,6 @@ DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
   //
   //===------------------------------------------------===//
 
-  // Move check blocks to their final position.
-  // TODO: Move as part of VPIRBB execute and update impacted tests.
-  if (BasicBlock *MemCheckBlock = ILV.RTChecks.getMemRuntimeChecks().second)
-    MemCheckBlock->moveAfter(EntryBB);
-  if (BasicBlock *SCEVCheckBlock = ILV.RTChecks.getSCEVChecks().second)
-    SCEVCheckBlock->moveAfter(EntryBB);
-
   BestVPlan.execute(&State);
 
   // 2.5 When vectorizing the epilogue, fix reduction resume values from the

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -493,6 +493,9 @@ void VPBasicBlock::connectToPredecessors(VPTransformState &State) {
 void VPIRBasicBlock::execute(VPTransformState *State) {
   assert(getHierarchicalSuccessors().size() <= 2 &&
          "VPIRBasicBlock can have at most two successors at the moment!");
+  // Move completely disconnected blocks to their final position.
+  if (IRBB->hasNPredecessors(0) && succ_begin(IRBB) == succ_end(IRBB))
+    IRBB->moveAfter(State->CFG.PrevBB);
   State->Builder.SetInsertPoint(IRBB->getTerminator());
   State->CFG.PrevBB = IRBB;
   State->CFG.VPBB2IRBB[this] = IRBB;