[Transforms] Use LLVMContext::MD_loop (NFC)

Author: kazutakahirata

llvm/lib/Transforms/Utils/BasicBlockUtils.cpp

@@ -1405,13 +1405,13 @@ SplitBlockPredecessorsImpl(BasicBlock *BB, ArrayRef<BasicBlock *> Preds,
   if (OldLatch) {
     BasicBlock *NewLatch = L->getLoopLatch();
     if (NewLatch != OldLatch) {
-      MDNode *MD = OldLatch->getTerminator()->getMetadata("llvm.loop");
-      NewLatch->getTerminator()->setMetadata("llvm.loop", MD);
+      MDNode *MD = OldLatch->getTerminator()->getMetadata(LLVMContext::MD_loop);
+      NewLatch->getTerminator()->setMetadata(LLVMContext::MD_loop, MD);
       // It's still possible that OldLatch is the latch of another inner loop,
       // in which case we do not remove the metadata.
       Loop *IL = LI->getLoopFor(OldLatch);
       if (IL && IL->getLoopLatch() != OldLatch)
-        OldLatch->getTerminator()->setMetadata("llvm.loop", nullptr);
+        OldLatch->getTerminator()->setMetadata(LLVMContext::MD_loop, nullptr);
     }
   }