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 fd7944c..84de4a6 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
@@ -1,13 +1,16 @@
 package org.teachfx.antlr4.ep20.pass.cfg;
 
 import org.jetbrains.annotations.NotNull;
+
 import org.teachfx.antlr4.ep20.ir.IRNode;
+import org.teachfx.antlr4.ep20.ir.expr.Operand;
 import org.teachfx.antlr4.ep20.ir.stmt.Label;
 import org.teachfx.antlr4.ep20.utils.Kind;
 
 import java.util.Iterator;
 import java.util.List;
 import java.util.Optional;
+import java.util.Set;
 
 public class BasicBlock<I extends IRNode> implements Iterable<Loc<I>> {
 
@@ -57,6 +60,23 @@ public int getId() {
     public boolean isEmpty() {
         return codes.isEmpty();
     }
+    public List<Loc<I>> allSeq() {
+        if (kind.equals(Kind.CONTINUOUS)){
+            return codes;
+        }
+        return codes.subList(0, codes.size() - 1);
+    }
+
+    public I getLastInstr() {
+        return codes.get(codes.size() - 1).instr;
+    }
+
+    // For data flow analysis
+    public Set<Operand> def;
+
+    public Set<Operand> liveUse;
 
+    public Set<Operand> liveIn;
 
+    public Set<Operand> liveOut;
 }
\ No newline at end of file
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/CFG.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/CFG.java
index b276dd0..8847590 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/CFG.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/CFG.java
@@ -1,21 +1,19 @@
 package org.teachfx.antlr4.ep20.pass.cfg;
 
 import org.apache.commons.lang3.tuple.Pair;
+import org.jetbrains.annotations.NotNull;
 import org.teachfx.antlr4.ep20.ir.IRNode;
 
-import java.util.ArrayList;
-import java.util.List;
-import java.util.Set;
-import java.util.TreeSet;
+import java.util.*;
 
-public class CFG {
-    public final List<IRNode> nodes;
+public class CFG<I extends IRNode> implements Iterable<BasicBlock<I>> {
+    public final List<BasicBlock<I>> nodes;
 
     public final List<Pair<Integer,Integer>> edges;
 
     private List<Pair<Set<Integer>, Set<Integer>>> links;
 
-    public CFG(List<IRNode> nodes, List<Pair<Integer, Integer>> edges) {
+    public CFG(List<BasicBlock<I>> nodes, List<Pair<Integer, Integer>> edges) {
         // Generate init
         this.nodes = nodes;
         this.edges = edges;
@@ -33,4 +31,30 @@ public CFG(List<IRNode> nodes, List<Pair<Integer, Integer>> edges) {
 
         }
     }
+
+    public BasicBlock<I> getBlock(int id) {
+        return nodes.get(id);
+    }
+
+    public Set<Integer> getPrev(int id) {
+        return links.get(id).getLeft();
+    }
+
+    public Set<Integer> getSucceed(int id) {
+        return links.get(id).getRight();
+    }
+
+    public int getInDegree(int id) {
+        return links.get(id).getLeft().size();
+    }
+
+    public int getOutDegree(int id) {
+        return links.get(id).getRight().size();
+    }
+
+    @NotNull
+    @Override
+    public Iterator<BasicBlock<I>> iterator() {
+        return nodes.iterator();
+    }
 }
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/CFGBuilder.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/CFGBuilder.java
index e9494bb..8082445 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/CFGBuilder.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/CFGBuilder.java
@@ -1,2 +1,11 @@
-package org.teachfx.antlr4.ep20.pass.cfg;public class CFGBuilder {
+package org.teachfx.antlr4.ep20.pass.cfg;
+
+import org.teachfx.antlr4.ep20.ir.IRNode;
+
+import java.util.List;
+
+public class CFGBuilder<I extends IRNode> {
+    public CFGBuilder(List<I> instrs){
+
+    }
 }
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/LinearIRBlock.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/LinearIRBlock.java
index 4a035c6..f07d74b 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/LinearIRBlock.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/pass/cfg/LinearIRBlock.java
@@ -1,10 +1,7 @@
 package org.teachfx.antlr4.ep20.pass.cfg;
 
 import org.teachfx.antlr4.ep20.ir.IRNode;
-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 org.teachfx.antlr4.ep20.ir.stmt.Stmt;
+import org.teachfx.antlr4.ep20.ir.stmt.*;
 import org.teachfx.antlr4.ep20.symtab.scope.Scope;
 import org.teachfx.antlr4.ep20.utils.Kind;
 
@@ -99,6 +96,12 @@ public void setScope(Scope scope) {
 
     @Override
     public String toString() {
+        var firstInstr = stmts.get(0);
+
+        if (firstInstr instanceof Label){
+            return firstInstr.toString();
+        }
+
         return "L"+ord;
     }