[llvm] [NFC][LoopVectorize] Make replaceVPBBWithIRVPBB more efficient (PR #111514)

[Paul Walker via llvm-commits]

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@@ -1005,12 +1005,14 @@ static void replaceVPBBWithIRVPBB(VPBasicBlock *VPBB, BasicBlock *IRBB) {
     R.moveBefore(*IRVPBB, IRVPBB->end());
   }
   VPBlockBase *PredVPBB = VPBB->getSinglePredecessor();
-  VPBlockUtils::disconnectBlocks(PredVPBB, VPBB);
-  VPBlockUtils::connectBlocks(PredVPBB, IRVPBB);
-  for (auto *Succ : to_vector(VPBB->getSuccessors())) {
-    VPBlockUtils::connectBlocks(IRVPBB, Succ);
-    VPBlockUtils::disconnectBlocks(VPBB, Succ);
-  }
+  PredVPBB->replaceSuccessor(VPBB, IRVPBB);
+  IRVPBB->setPredecessors({PredVPBB});
+  for (auto *Succ : to_vector(VPBB->getSuccessors()))
+    Succ->replacePredecessor(VPBB, IRVPBB);
+  IRVPBB->setSuccessors(VPBB->getSuccessors());
+
+  VPBB->clearSuccessors();
+  VPBB->clearPredecessors();
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paulwalker-arm wrote:

Are these necessary? I'd expect `delete VPBB` to be sufficient to clean up the SmallVectors?

https://github.com/llvm/llvm-project/pull/111514