[backend] debugging segmentation fault caused by branch instr

src/RISCv32Backend.h

@@ -7,6 +7,7 @@
 #include <map>
 #include <set>
 #include <memory>
+#include <iostream>
 
 namespace sysy {
 
@@ -19,7 +20,7 @@ public:
 
     // Move DAGNode and RegAllocResult to public section
     struct DAGNode {
-        enum NodeKind { CONSTANT, LOAD, STORE, BINARY, CALL, RETURN };
+        enum NodeKind { CONSTANT, LOAD, STORE, BINARY, CALL, RETURN, BRANCH };
         NodeKind kind;
         Value* value = nullptr;
         std::string inst;
@@ -52,6 +53,7 @@ public:
     RegAllocResult register_allocation(Function* func);
     void eliminate_phi(Function* func);
     std::string reg_to_string(PhysicalReg reg);
+    void print_dag(const std::vector<std::unique_ptr<DAGNode>>& dag, const std::string& bb_name);
 
 private:
     static const std::vector<PhysicalReg> allocable_regs;