[llvm] [SelectionDAG] Fix unsafe cases for loop.dependence.{war/raw}.mask (PR #168565)

[Benjamin Maxwell via llvm-commits]

================
@@ -1692,23 +1699,32 @@ void DAGTypeLegalizer::SplitVecRes_BITCAST(SDNode *N, SDValue &Lo,
   Hi = DAG.getNode(ISD::BITCAST, dl, HiVT, Hi);
 }
 
+/// Split a loop dependence mask.
----------------
MacDue wrote:

Not here, but can you update ISDOpcodes.h to mention the "lane offset":

```
  // The `llvm.loop.dependence.{war, raw}.mask` intrinsics
  // Operands: Load pointer, Store pointer, Element size, Lane offset
  // Output: Mask
  LOOP_DEPENDENCE_WAR_MASK,
  LOOP_DEPENDENCE_RAW_MASK,

```

https://github.com/llvm/llvm-project/pull/168565