[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/midend/IR.cpp

@@ -569,7 +569,7 @@ void User::replaceOperand(unsigned index, Value *value) {
  * phi相关函数
  */
 
- Value* PhiInst::getvalfromBlk(BasicBlock* blk){
+Value* PhiInst::getvalfromBlk(BasicBlock* blk){
   refreshB2VMap();
   if( blk2val.find(blk) != blk2val.end()) {
     return blk2val.at(blk);
@@ -619,11 +619,13 @@ void PhiInst::delBlk(BasicBlock* blk){
 
 void PhiInst::replaceBlk(BasicBlock* newBlk, unsigned k){
   refreshB2VMap();
-  Value* val = blk2val.at(getBlock(k));
+  BasicBlock* oldBlk = getBlock(k);
+  Value* val = blk2val.at(oldBlk);
+  // Value* val = blk2val.at(getBlock(k));
   // 替换基本块
   setOperand(2 * k + 1, newBlk);
   // 替换blk2val映射
-  blk2val.erase(getBlock(k));
+  blk2val.erase(oldBlk);
   blk2val.emplace(newBlk, val);
 }