Invalid func fix pt2 (#409)

* return decl instead of nullptr

* return error/null instead of decl

lib/Lifters/FunctionLifter.cpp

@@ -409,13 +409,6 @@ llvm::Function *FunctionLifter::LiftFunction(const FunctionDecl &decl) {
     return nullptr;
   }
 
-  // Function has no valid instructions.
-  auto &cfg = decl.cfg;
-  if (cfg.find(decl.entry_uid) == cfg.end()) {
-    LOG(ERROR) << "Function missing entry block " << std::hex << decl.address;
-    return nullptr;
-  }
-
   // This is our higher-level function, i.e. it presents itself more like
   // a function compiled from C/C++, rather than being a three-argument Remill
   // function. In this function, we will stack-allocate a `State` structure,
@@ -440,6 +433,14 @@ llvm::Function *FunctionLifter::LiftFunction(const FunctionDecl &decl) {
     return native_func;
   }
 
+  // Function has no valid instructions.
+  auto &cfg = decl.cfg;
+  if (cfg.find(decl.entry_uid) == cfg.end()) {
+    LOG(ERROR) << "Function missing entry block " << std::hex << decl.address;
+    return nullptr;
+  }
+
+
   // Every lifted function starts as a clone of __remill_basic_block. That
   // prototype has multiple arguments (memory pointer, state pointer, program
   // counter). This extracts the state pointer.