fix: skip empty functions, relax jump-threading to handle multi-instr jmp stubs

cfg/builder.cpp

@@ -458,12 +458,19 @@ CFG CFGBuilder::build()
     set<addr_t> built;
     queue<addr_t> pending;
 
+    auto isEmpty = [](const Function& f) -> bool {
+        for (const auto& b : f.blocks)
+            if (!b.instructions.empty()) return false;
+        return true;
+    };
+
     auto process = [&](addr_t addr, const string& name)
     {
         if (built.count(addr)) return;
         built.insert(addr);
 
         auto func = buildFunction(addr, name);
+        if (isEmpty(func)) return;
         cfg.functions.push_back(func);
 
         for (const auto& b : func.blocks)
@@ -513,6 +520,7 @@ CFG CFGBuilder::build()
 
         built.insert(a);
         auto func = buildFunction(a, name);
+        if (isEmpty(func)) continue;
         cfg.functions.push_back(func);
 
         for (const auto& b : func.blocks)
@@ -616,8 +624,8 @@ static void jumpThread(CFG& cfg)
                 if (addr_to_func[t] != &func) continue;
 
                 BasicBlock* target = it->second;
-                if (target->instructions.size() == 1 &&
-                    target->instructions[0].mnemonic == "jmp" &&
+                if (!target->instructions.empty() &&
+                    target->instructions.back().mnemonic == "jmp" &&
                     target->successors.size() == 1)
                 {
                     addr_t redirect = target->successors[0];