[SandboxVec][DAG][NFC] Remove early return in notifyMoveInstr()

It used to early return when destination is same as origin. But it's redundant
because in that case the callback won't get called in the first place.

Author: vporpo

llvm/lib/Transforms/Vectorize/SandboxVectorizer/DependencyGraph.cpp

@@ -368,10 +368,11 @@ void DependencyGraph::notifyCreateInstr(Instruction *I) {
 }
 
 void DependencyGraph::notifyMoveInstr(Instruction *I, const BBIterator &To) {
-  // Early return if `I` doesn't actually move.
+  // NOTE: This function runs before `I` moves to its new destination.
   BasicBlock *BB = To.getNodeParent();
-  if (To != BB->end() && &*To == I->getNextNode())
-    return;
+  assert(!(To != BB->end() && &*To == I->getNextNode()) &&
+         !(To == BB->end() && std::next(I->getIterator()) == BB->end()) &&
+         "Should not have been called if destination is same as origin.");
 
   // Maintain the DAGInterval.
   DAGInterval.notifyMoveInstr(I, To);