diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/IRVisitor.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/IRVisitor.java
index 2bcccea..2cb389e 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/IRVisitor.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/IRVisitor.java
@@ -2,7 +2,7 @@
 
 import org.teachfx.antlr4.ep20.ir.expr.CallFunc;
 import org.teachfx.antlr4.ep20.ir.expr.addr.FrameSlot;
-import org.teachfx.antlr4.ep20.ir.expr.addr.StackSlot;
+import org.teachfx.antlr4.ep20.ir.expr.addr.OperandSlot;
 import org.teachfx.antlr4.ep20.ir.expr.arith.BinExpr;
 import org.teachfx.antlr4.ep20.ir.expr.arith.UnaryExpr;
 import org.teachfx.antlr4.ep20.ir.expr.val.ConstVal;
@@ -28,7 +28,7 @@ public interface IRVisitor<S,E> {
 
     S visit(Prog prog);
 
-    E visit(StackSlot stackSlot);
+    E visit(OperandSlot operandSlot);
 
     E visit(FrameSlot frameSlot);
 
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/expr/CallFunc.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/expr/CallFunc.java
index e9fd6a7..2d8ebc8 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/expr/CallFunc.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/expr/CallFunc.java
@@ -2,11 +2,8 @@
 
 
 import org.teachfx.antlr4.ep20.ir.IRVisitor;
-import org.teachfx.antlr4.ep20.ir.expr.addr.StackSlot;
 import org.teachfx.antlr4.ep20.symtab.symbol.MethodSymbol;
 
-import java.util.List;
-
 public class CallFunc extends Expr {
     protected MethodSymbol funcType;
     protected String funcName;
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/expr/addr/StackSlot.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/expr/addr/OperandSlot.java
similarity index 68%
rename from ep20/src/main/java/org/teachfx/antlr4/ep20/ir/expr/addr/StackSlot.java
rename to ep20/src/main/java/org/teachfx/antlr4/ep20/ir/expr/addr/OperandSlot.java
index e0de618..94109c2 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/expr/addr/StackSlot.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/expr/addr/OperandSlot.java
@@ -3,16 +3,16 @@
 import org.teachfx.antlr4.ep20.ir.IRVisitor;
 import org.teachfx.antlr4.ep20.ir.expr.VarSlot;
 
-public class StackSlot extends VarSlot {
+public class OperandSlot extends VarSlot {
     private static int ordSeq = 0;
 
-    public static StackSlot genTemp() {
-        return new StackSlot();
+    public static OperandSlot genTemp() {
+        return new OperandSlot();
     }
 
     private int ord = 0;
-    private StackSlot() {
-        this.ord = StackSlot.ordSeq++;
+    private OperandSlot() {
+        this.ord = OperandSlot.ordSeq++;
     }
     public int getOrd() {
         return ord;
@@ -29,7 +29,7 @@ public <S, E> E accept(IRVisitor<S, E> visitor) {
     }
 
 
-    public static StackSlot pushStack() { return StackSlot.genTemp(); }
+    public static OperandSlot pushStack() { return OperandSlot.genTemp(); }
     public static void popStack() { ordSeq--;}
 
     public static int getOrdSeq() {
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/expr/arith/UnaryExpr.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/expr/arith/UnaryExpr.java
index 40a30d5..8a59bd8 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/expr/arith/UnaryExpr.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/expr/arith/UnaryExpr.java
@@ -3,7 +3,6 @@
 import org.teachfx.antlr4.ep20.ir.IRVisitor;
 import org.teachfx.antlr4.ep20.ir.expr.Expr;
 import org.teachfx.antlr4.ep20.ir.expr.VarSlot;
-import org.teachfx.antlr4.ep20.ir.expr.addr.StackSlot;
 import org.teachfx.antlr4.ep20.symtab.type.OperatorType;
 import org.teachfx.antlr4.ep20.symtab.type.OperatorType.UnaryOpType;
 
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/BasicBlock.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/BasicBlock.java
index f1f16bf..1fc3687 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/BasicBlock.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/BasicBlock.java
@@ -2,7 +2,6 @@
 
 import org.teachfx.antlr4.ep20.ir.IRNode;
 import org.teachfx.antlr4.ep20.ir.stmt.CJMP;
-import org.teachfx.antlr4.ep20.ir.stmt.FuncEntryLabel;
 import org.teachfx.antlr4.ep20.ir.stmt.JMP;
 import org.teachfx.antlr4.ep20.ir.stmt.Stmt;
 import org.teachfx.antlr4.ep20.symtab.scope.Scope;
@@ -93,6 +92,11 @@ public void setJmpRefMap(List<IRNode> jmpRefMap) {
         this.jmpRefMap = jmpRefMap;
     }
 
+    public int getOrd() {
+        return ord;
+    }
+
+
     public void refJMP(IRNode node) {
         jmpRefMap.add(node);
     }
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/ControlFlowAnalysis.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/ControlFlowAnalysis.java
index dfb993d..83fd763 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/ControlFlowAnalysis.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/ControlFlowAnalysis.java
@@ -4,7 +4,7 @@
 import org.teachfx.antlr4.ep20.ir.Prog;
 import org.teachfx.antlr4.ep20.ir.expr.CallFunc;
 import org.teachfx.antlr4.ep20.ir.expr.addr.FrameSlot;
-import org.teachfx.antlr4.ep20.ir.expr.addr.StackSlot;
+import org.teachfx.antlr4.ep20.ir.expr.addr.OperandSlot;
 import org.teachfx.antlr4.ep20.ir.expr.arith.BinExpr;
 import org.teachfx.antlr4.ep20.ir.expr.arith.UnaryExpr;
 import org.teachfx.antlr4.ep20.ir.expr.val.ConstVal;
@@ -68,7 +68,7 @@ public Void visit(Prog prog) {
     }
 
     @Override
-    public Void visit(StackSlot stackSlot) {
+    public Void visit(OperandSlot operandSlot) {
         return null;
     }
 
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/LivenessAnalysis.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/LivenessAnalysis.java
index d9a1b8b..4c35569 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/LivenessAnalysis.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/LivenessAnalysis.java
@@ -4,7 +4,7 @@
 import org.teachfx.antlr4.ep20.ir.Prog;
 import org.teachfx.antlr4.ep20.ir.expr.CallFunc;
 import org.teachfx.antlr4.ep20.ir.expr.addr.FrameSlot;
-import org.teachfx.antlr4.ep20.ir.expr.addr.StackSlot;
+import org.teachfx.antlr4.ep20.ir.expr.addr.OperandSlot;
 import org.teachfx.antlr4.ep20.ir.expr.arith.BinExpr;
 import org.teachfx.antlr4.ep20.ir.expr.arith.UnaryExpr;
 import org.teachfx.antlr4.ep20.ir.expr.val.ConstVal;
@@ -58,7 +58,7 @@ public Void visit(Prog prog) {
     }
 
     @Override
-    public Void visit(StackSlot stackSlot) {
+    public Void visit(OperandSlot operandSlot) {
         return null;
     }
 
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/codegen/CymbolAssembler.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/codegen/CymbolAssembler.java
index dfe9149..05f7f85 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/codegen/CymbolAssembler.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/codegen/CymbolAssembler.java
@@ -5,7 +5,7 @@
 import org.teachfx.antlr4.ep20.ir.expr.CallFunc;
 import org.teachfx.antlr4.ep20.ir.expr.Expr;
 import org.teachfx.antlr4.ep20.ir.expr.addr.FrameSlot;
-import org.teachfx.antlr4.ep20.ir.expr.addr.StackSlot;
+import org.teachfx.antlr4.ep20.ir.expr.addr.OperandSlot;
 import org.teachfx.antlr4.ep20.ir.expr.arith.BinExpr;
 import org.teachfx.antlr4.ep20.ir.expr.arith.UnaryExpr;
 import org.teachfx.antlr4.ep20.ir.expr.val.ConstVal;
@@ -119,7 +119,7 @@ public Void visit(ReturnVal returnVal) {
     }
 
     @Override
-    public Void visit(StackSlot stackSlot) {
+    public Void visit(OperandSlot operandSlot) {
         return null;
     }
 
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/ir/CymbolIRBuilder.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/ir/CymbolIRBuilder.java
index bba2d60..df202ce 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/ir/CymbolIRBuilder.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/ir/CymbolIRBuilder.java
@@ -17,7 +17,7 @@
 import org.teachfx.antlr4.ep20.ir.expr.CallFunc;
 import org.teachfx.antlr4.ep20.ir.expr.VarSlot;
 import org.teachfx.antlr4.ep20.ir.expr.addr.FrameSlot;
-import org.teachfx.antlr4.ep20.ir.expr.addr.StackSlot;
+import org.teachfx.antlr4.ep20.ir.expr.addr.OperandSlot;
 import org.teachfx.antlr4.ep20.ir.expr.arith.BinExpr;
 import org.teachfx.antlr4.ep20.ir.expr.arith.UnaryExpr;
 import org.teachfx.antlr4.ep20.ir.expr.val.ConstVal;
@@ -330,10 +330,10 @@ public Optional<VarSlot> addInstr(IRNode stmt) {
         if (stmt instanceof BinExpr) {
             popEvalOperand();
             popEvalOperand();
-            return Optional.of(StackSlot.pushStack());
+            return Optional.of(OperandSlot.pushStack());
         } else if (stmt instanceof UnaryExpr) {
             popEvalOperand();
-            return Optional.of(StackSlot.pushStack());
+            return Optional.of(OperandSlot.pushStack());
         } else if(stmt instanceof CJMP) {
             popEvalOperand();
         } else if (stmt instanceof CallFunc callFunc) {
@@ -345,7 +345,7 @@ public Optional<VarSlot> addInstr(IRNode stmt) {
             }
             // 如果存在返回值，则要模拟压入返回值以保证栈平衡
             if(!callFunc.getFuncType().isVoid()) {
-               pushEvalOperand(StackSlot.genTemp());
+               pushEvalOperand(OperandSlot.genTemp());
             }
         }
 
@@ -388,9 +388,9 @@ protected VarSlot pushEvalOperand(Temp temp) {
             logger.info(curNode.toString());
         }
 
-        if (!(temp instanceof StackSlot)){
+        if (!(temp instanceof OperandSlot)){
             cnt++;
-            var assignee = StackSlot.pushStack();
+            var assignee = OperandSlot.pushStack();
             evalExprStack.push(assignee);
             addInstr(Assign.with(assignee, temp));
             logger.info("-> eval stack %s%n", evalExprStack.toString());
@@ -408,8 +408,8 @@ protected VarSlot popEvalOperand() {
         var res = evalExprStack.pop();
         logger.info("pop eval operand %s",res);
         logger.info("pop stack");
-        StackSlot.popStack();
-        if (StackSlot.getOrdSeq() < 0) {
+        OperandSlot.popStack();
+        if (OperandSlot.getOrdSeq() < 0) {
             throw new RuntimeException("un matched pop");
         }
         return res;
diff --git a/ep20/src/test/java/org/teachfx/antlr4/ep20/ast/expr/BoolExprNodeTest.java b/ep20/src/test/java/org/teachfx/antlr4/ep20/ast/expr/BoolExprNodeTest.java
index da72305..c14770a 100644
--- a/ep20/src/test/java/org/teachfx/antlr4/ep20/ast/expr/BoolExprNodeTest.java
+++ b/ep20/src/test/java/org/teachfx/antlr4/ep20/ast/expr/BoolExprNodeTest.java
@@ -1,2 +1,3 @@
-package org.teachfx.antlr4.ep20.ast.expr;public class BoolExprNodeTest {
+package org.teachfx.antlr4.ep20.ast.expr;
+public class BoolExprNodeTest {
 }
diff --git a/ep20/src/test/java/org/teachfx/antlr4/ep20/pass/codegen/CymbolAssemblerTest.java b/ep20/src/test/java/org/teachfx/antlr4/ep20/pass/codegen/CymbolAssemblerTest.java
index 35a1bbb..28f78f2 100644
--- a/ep20/src/test/java/org/teachfx/antlr4/ep20/pass/codegen/CymbolAssemblerTest.java
+++ b/ep20/src/test/java/org/teachfx/antlr4/ep20/pass/codegen/CymbolAssemblerTest.java
@@ -2,13 +2,7 @@
 
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
-import org.teachfx.antlr4.ep20.ir.expr.arith.BinExpr;
-import org.teachfx.antlr4.ep20.ir.expr.arith.UnaryExpr;
-import org.teachfx.antlr4.ep20.ir.expr.val.ConstVal;
-import org.teachfx.antlr4.ep20.ir.stmt.Assign;
-import org.teachfx.antlr4.ep20.ir.stmt.CJMP;
-import org.teachfx.antlr4.ep20.ir.stmt.JMP;
-import org.teachfx.antlr4.ep20.ir.stmt.ReturnVal;
+
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
diff --git a/ep21/TODO.md b/ep21/TODO.md
index f99a0ea..0159477 100644
--- a/ep21/TODO.md
+++ b/ep21/TODO.md
@@ -8,8 +8,8 @@
   - [ ] 线性化MIR输出
 
 - [ ] CFG
-  - [ ] 基本块划分
-  - [ ] 关系生成
+  - [x] 基本块划分
+  - [x] 关系生成
   - [ ] 生成DOT 
 
 ## Todo