[llvm] [SelectionDAG] Split sd_use_iterator into sd_user_iterator and sd_use_iterator. (PR #120531)

[Jay Foad via llvm-commits]

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@@ -837,29 +835,72 @@ END_TWO_BYTE_PACK()
     }
   };
 
+  class user_iterator {
+    friend class SDNode;
+    use_iterator UI;
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jayfoad wrote:

This might be a silly question but can you implement this as `class user_iterator : use_iterator` and just override `value_type` and `operator*`?

https://github.com/llvm/llvm-project/pull/120531