[midend]将alloca声明统一到entry块，增加mem2reg的机会，TODO：不是很明白为什么开了优化过不了一些样例正在排查原因

src/midend/Pass/Pass.cpp

@@ -108,6 +108,10 @@ void PassManager::runOptimizationPipeline(Module* moduleIR, IRBuilder* builderIR
         printPasses();
       }
 
+      this->clearPasses();
+      this->addPass(&DCE::ID); 
+      this->run();
+
       if (DEBUG) std::cout << "--- Custom optimization sequence finished ---\n";
     }
 

src/midend/SysYIRGenerator.cpp

@@ -586,7 +586,18 @@ std::any SysYIRGenerator::visitConstDecl(SysYParser::ConstDeclContext *ctx) {
 
     // 显式地为局部常量在栈上分配空间
     // alloca 的类型将是指针指向常量类型，例如 `int*` 或 `int[2][3]*`
+    // 将 alloca 全部集中到entry函数中
+    // 记录当前位置
+    BasicBlock *curBB = builder.getBasicBlock();
+    auto curPos =builder.getPosition();
+    Function *currentFunction = builder.getBasicBlock()->getParent();
+    BasicBlock *entryBB = currentFunction->getEntryBlock();
+    // 在terminator前插入
+    auto entryPos = entryBB->terminator();
+    builder.setPosition(entryBB, entryPos);
     AllocaInst *alloca = builder.createAllocaInst(Type::getPointerType(variableType), name);
+    // 恢复当前位置
+    builder.setPosition(curBB, curPos);
 
     ArrayValueTree *root = std::any_cast<ArrayValueTree *>(constDef->constInitVal()->accept(this));
     ValueCounter values;
@@ -743,8 +754,20 @@ std::any SysYIRGenerator::visitVarDecl(SysYParser::VarDeclContext *ctx) {
 
     // 对于数组，alloca 的类型将是指针指向数组类型，例如 `int[2][3]*`
     // 对于标量，alloca 的类型将是指针指向标量类型，例如 `int*`
-    AllocaInst* alloca =
-        builder.createAllocaInst(Type::getPointerType(variableType), name);
+
+    BasicBlock *curBB = builder.getBasicBlock();
+    auto curPos =builder.getPosition();
+    Function *currentFunction = builder.getBasicBlock()->getParent();
+    BasicBlock *entryBB = currentFunction->getEntryBlock();
+    // 在terminator前插入
+    auto entryPos = entryBB->terminator();
+    builder.setPosition(entryBB, entryPos);
+    AllocaInst *alloca = builder.createAllocaInst(Type::getPointerType(variableType), name);
+    // 恢复当前位置
+    builder.setPosition(curBB, curPos);
+
+    // AllocaInst* alloca =
+    //     builder.createAllocaInst(Type::getPointerType(variableType), name);
 
     if (varDef->initVal() != nullptr) {
       ValueCounter values;