Lab4: Implement basic scalar optimizations and lower Phi nodes to assembly

src/ir/passes/DCE.cpp

@@ -1,4 +1,75 @@
-// 死代码删除（DCE）：
-// - 删除无用指令与无用基本块
-// - 通常与 CFG 简化配合使用
+#include "ir/PassManager.h"
+#include <iostream>
+#include <unordered_set>
+#include <queue>
+#include <vector>
 
+namespace ir {
+
+bool RunDCE(Function* func) {
+  std::unordered_set<Instruction*> live_instructions;
+  std::queue<Instruction*> worklist;
+
+  // 1. Mark inherently live instructions
+  for (const auto& bbPtr : func->GetBlocks()) {
+    for (const auto& instPtr : bbPtr->GetInstructions()) {
+      auto* inst = instPtr.get();
+      bool inherently_live = false;
+
+      switch (inst->GetOpcode()) {
+        case Opcode::Ret:
+        case Opcode::Br:
+        case Opcode::Store:
+        case Opcode::Call:
+          inherently_live = true;
+          break;
+        default:
+          break;
+      }
+
+      if (inherently_live) {
+        live_instructions.insert(inst);
+        worklist.push(inst);
+      }
+    }
+  }
+
+  // 2. Propagate liveness along the def-use chains
+  while (!worklist.empty()) {
+    auto* inst = worklist.front();
+    worklist.pop();
+
+    for (size_t i = 0; i < inst->GetNumOperands(); ++i) {
+      auto* operand = inst->GetOperand(i);
+      if (auto* op_inst = dynamic_cast<Instruction*>(operand)) {
+        if (live_instructions.find(op_inst) == live_instructions.end()) {
+          live_instructions.insert(op_inst);
+          worklist.push(op_inst);
+        }
+      }
+    }
+  }
+
+  // 3. Sweep dead instructions
+  bool changed = false;
+  for (const auto& bbPtr : func->GetBlocks()) {
+    std::vector<Instruction*> dead_instructions;
+    for (const auto& instPtr : bbPtr->GetInstructions()) {
+      auto* inst = instPtr.get();
+      if (live_instructions.find(inst) == live_instructions.end()) {
+        dead_instructions.push_back(inst);
+      }
+    }
+
+    if (!dead_instructions.empty()) {
+      changed = true;
+      for (auto* inst : dead_instructions) {
+        bbPtr->EraseInstruction(inst);
+      }
+    }
+  }
+
+  return changed;
+}
+
+} // namespace ir