Sometimes the debug scope already attached to a SILFunction before

deserialization contains AST information which is needed in certain
cases. Do not overwrite the debug scope in that case

Author: usama54321

lib/Serialization/DeserializeSIL.cpp

@@ -1131,7 +1131,8 @@ llvm::Expected<SILFunction *> SILDeserializer::readSILFunctionChecked(
 
       auto Scope = maybeScope.get();
       if (isFirstScope) {
-        fn->setDebugScope(Scope);
+        if (!fn->getDebugScope() || fn->getDebugScope()->getLoc().isAutoGenerated())
+          fn->setDebugScope(Scope);
         isFirstScope = false;
       }
       Builder.setCurrentDebugScope(Scope);

test/Serialization/debug-value.swift

@@ -50,3 +50,4 @@ func test() {
 // CHECK: debug_value {{.*}} : $Builtin.Int64, var, (name "temp", loc "{{.*}}MyModule.swift":3:9, scope {{.*}}), type $Int64, expr op_fragment:#Int64._value, loc "{{.*}}MyModule.swift":5:14, scope
 
 test()
+// CHECK-NOT: UnknownCode