[llvm] [CodeGen] Port GlobalMerge to new pass manager (PR #77474)

[Matt Arsenault via llvm-commits]

================
@@ -290,6 +291,9 @@ template <typename DerivedT> class CodeGenPassBuilder {
                                    inconvertibleErrorCode());
   }
 
+  /// Target can override this to add GlobalMergePass before all IR passes.
+  void addGlobalMergePass(AddIRPass &) const {}
----------------
arsenm wrote:

Why is this here? Is there an analogous hook in the old PM?

https://github.com/llvm/llvm-project/pull/77474