[Prototype] Mark main entry function as preserved

Author: kateinoigakukun

lib/Serialization/ModuleSummaryIndexer.cpp

@@ -302,6 +302,10 @@ void FunctionSummaryIndexer::visitKeyPathInst(KeyPathInst *KPI) {
 }
 
 bool shouldPreserveFunction(const SILFunction &F) {
+  if (F.getName().equals(SWIFT_ENTRY_POINT_FUNCTION)) {
+    return true;
+  }
+
   if (F.getRepresentation() == SILFunctionTypeRepresentation::ObjCMethod) {
     return true;
   }

tools/driver/cross_module_opt_main.cpp

@@ -37,7 +37,6 @@ static llvm::cl::opt<std::string>
 
 static llvm::DenseSet<GUID> computePreservedGUIDs(ModuleSummaryIndex *summary) {
   llvm::DenseSet<GUID> Set(1);
-  Set.insert(getGUIDFromUniqueName("main"));
   for (auto FI = summary->functions_begin(), FE = summary->functions_end();
        FI != FE; ++FI) {
     auto summary = FI->second.get();