fix(mir)修复Ret返回void问题

src/mir/AsmPrinter.cpp

@@ -314,7 +314,6 @@ void PrintAsm(const MachineFunction& function, std::ostream& os) {
 void PrintAsm(const MachineModule& module, std::ostream& os) {
   // 输出文件头
   os << ".arch armv8-a\n";
-  os << ".text\n";
   
   DEBUG_MSG("module");
   // 遍历所有函数，输出汇编

src/mir/FrameLowering.cpp

@@ -5,7 +5,7 @@
 
 #include "utils/Log.h"
 
-#define DEBUG_Frame
+//#define DEBUG_Frame
 
 #ifdef DEBUG_Frame
 #include <iostream>

src/mir/Lowering.cpp

@@ -7,7 +7,7 @@
 #include "ir/IR.h"
 #include "utils/Log.h"
 
-#define DEBUG_Lower
+//#define DEBUG_Lower
 
 #ifdef DEBUG_Lower
 #include <iostream>
@@ -125,6 +125,9 @@ void EmitValueToReg(const ir::Value* value, PhysReg target,
                     const ValueSlotMap& slots, MachineBasicBlock& block,
                     MachineFunction& function) {
   // 处理整数常量
+  if (value == nullptr) {
+    DEBUG_MSG( "EmitValueToReg called with null value\n");
+  }
   if (auto* constant = dynamic_cast<const ir::ConstantInt*>(value)) {
     block.Append(Opcode::MovImm,
                  {Operand::Reg(target), Operand::Imm(constant->GetValue())});
@@ -219,7 +222,6 @@ void LowerInstruction(const ir::Instruction& inst, MachineFunction& function,
   //auto& block = function.GetEntry();
   DEBUG_MSG("Processing instruction: " << inst.GetName() 
               << " (opcode: " << static_cast<int>(inst.GetOpcode()) << ")");
-
   switch (inst.GetOpcode()) {
     case ir::Opcode::Alloca: {
       slots.emplace(&inst, function.CreateFrameIndex(GetTypeSize(inst.GetType().get())));
@@ -326,7 +328,10 @@ void LowerInstruction(const ir::Instruction& inst, MachineFunction& function,
     }
     case ir::Opcode::Ret: {
       auto& ret = static_cast<const ir::ReturnInst&>(inst);
-      EmitValueToReg(ret.GetValue(), PhysReg::W0, slots, block, function);
+      const ir::Value* retVal = ret.GetValue();
+      if (retVal != nullptr) {
+          EmitValueToReg(retVal, PhysReg::W0, slots, block, function);
+      }
       block.Append(Opcode::Ret);
       return;
     }