[llvm] [CodeGen] Expose the extensibility of PassConfig to plugins (PR #139059)

[Matt Arsenault via llvm-commits]

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@@ -119,6 +119,9 @@ addPassesToGenerateCode(CodeGenTargetMachineImpl &TM, PassManagerBase &PM,
   PM.add(PassConfig);
   PM.add(&MMIWP);
 
+  for (auto& C : *TargetMachine::TargetPassConfigCallbacks)
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arsenm wrote:

LLVM style is supposed to be almost never auto, and I don't think the type here is that obvious 

https://github.com/llvm/llvm-project/pull/139059