[ArgPromo] Preserve FunctionAnalysisManagerCGSCCProxy

We already make sure to properly clear analyses for deleted functions.

This makes investigating some future potential compile time improvements easier.

Reviewed By: asbirlea

Differential Revision: https://reviews.llvm.org/D113032

Author: aeubanks

llvm/lib/Transforms/IPO/ArgumentPromotion.cpp

@@ -1051,7 +1051,10 @@ PreservedAnalyses ArgumentPromotionPass::run(LazyCallGraph::SCC &C,
   if (!Changed)
     return PreservedAnalyses::all();
 
-  return PreservedAnalyses::none();
+  PreservedAnalyses PA;
+  // We've cleared out analyses for deleted functions.
+  PA.preserve<FunctionAnalysisManagerCGSCCProxy>();
+  return PA;
 }
 
 namespace {