[midend-SCCP]bug修复，增加不可达指令（理论来说后端不会出现这条指令，只是为了IR完整性添加），添加相关方法，phi指令方法修复；目前能够跑完所有优化，但是User的析构函数重定义导致全局析构不能正确完成，需要修复

src/include/midend/IR.h

@@ -710,7 +710,7 @@ class Instruction : public User {
     kCondBr = 0x1UL << 30,
     kBr = 0x1UL << 31,
     kReturn = 0x1UL << 32,
-    kUnreachable = 0x1UL << 32,  ///< Unreachable instruction, used for optimization purposes
+    kUnreachable = 0x1UL << 33,
     // mem op
     kAlloca = 0x1UL << 34,
     kLoad = 0x1UL << 35,
@@ -845,7 +845,7 @@ public:
     return kind & MemoryOpMask;
   }
   bool isTerminator() const {
-    static constexpr uint64_t TerminatorOpMask = kCondBr | kBr | kReturn;
+    static constexpr uint64_t TerminatorOpMask = kCondBr | kBr | kReturn | kUnreachable;
     return kind & TerminatorOpMask;
   }
   bool isCmp() const {
@@ -874,6 +874,7 @@ public:
   bool isMemset() const { return kind == kMemset; }
   bool isCall() const { return kind == kCall; }
   bool isReturn() const { return kind == kReturn; }
+  bool isUnreachable() const { return kind == kUnreachable; }
   bool isDefine() const {
     static constexpr uint64_t DefineOpMask = kAlloca | kStore | kPhi;
     return (kind & DefineOpMask) != 0U;