diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/Compiler.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/Compiler.java
index 41cc9a5..ab216e8 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/Compiler.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/Compiler.java
@@ -48,8 +48,11 @@ public static void main(String[] args) throws IOException {
         var irBuilder = new CymbolIRBuilder();
 
         astRoot.accept(irBuilder);
-        for(var block : irBuilder.prog.blockList) {
-            var cfg = irBuilder.getCFG(List.of(block));
+
+        irBuilder.prog.optimizeBasicBlock();
+
+        for(var funBlock : irBuilder.prog.blockList) {
+            var cfg = irBuilder.getCFG(funBlock);
             logger.info("CFG:\n" + cfg.toString());
         }
 
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/Prog.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/Prog.java
index 130a540..46e4fd2 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/Prog.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/Prog.java
@@ -9,10 +9,7 @@
 import org.teachfx.antlr4.ep20.ir.stmt.Label;
 import org.teachfx.antlr4.ep20.pass.cfg.LinearIRBlock;
 
-import java.util.ArrayList;
-import java.util.LinkedList;
-import java.util.List;
-import java.util.Objects;
+import java.util.*;
 
 
 public class Prog extends IRNode {
@@ -33,14 +30,14 @@ public <S,E> S accept(IRVisitor<S,E> visitor){
     public void addBlock(LinearIRBlock linearIRBlock) {
         blockList.add(linearIRBlock);
     }
+    protected TreeSet<LinearIRBlock> needRemovedBlocks = new TreeSet<>();
 
-    private void linearInstrsImpl(@NotNull LinearIRBlock linearIRBlock) {
-        // Add all instr from non-empty block
-        if (!linearIRBlock.getStmts().isEmpty()) {
-            instrs.addAll(linearIRBlock.getStmts());
-        } else {
+    private void optimizeEmptyBlock(@NotNull LinearIRBlock linearIRBlock) {
+        // replace empty block within non-empty first successor
+        if (linearIRBlock.getStmts().isEmpty()){
             // Drop empty block
             if (linearIRBlock.getSuccessors().isEmpty()) {
+                needRemovedBlocks.add(linearIRBlock);
                 return;
             }
             // Auto-fill next block for jmp/cjmp
@@ -48,16 +45,60 @@ private void linearInstrsImpl(@NotNull LinearIRBlock linearIRBlock) {
             for (var ref : linearIRBlock.getJmpRefMap()){
                 if (ref instanceof JMP jmp) {
                     jmp.setNext(nextBlock);
+
                 } else if (ref instanceof CJMP cjmp) {
                     cjmp.setElseBlock(nextBlock);
                 }
             }
 
+            linearIRBlock.getPredecessors().forEach(prev -> {
+                prev.removeSuccessor(linearIRBlock);
+                prev.getSuccessors().add(nextBlock);
+            });
+
+            needRemovedBlocks.add(linearIRBlock);
         }
 
         // recursive call
         for(var successor : linearIRBlock.getSuccessors()){
-            linearInstrsImpl(successor);
+            optimizeEmptyBlock(successor);
+        }
+    }
+
+    private void insertLabelForBlock(LinearIRBlock startBlock) {
+        for (var stmt : startBlock.getStmts()) {
+            if (stmt instanceof Label) {
+                break;
+            }
+
+            startBlock.insertStmt(new Label(startBlock.getScope(), startBlock.getOrd()),0);
+            break; // only insert one label for each block which is not func-entry block.
+        }
+
+        for (var successor : startBlock.getSuccessors()) {
+            insertLabelForBlock(successor);
+        }
+    }
+    protected void buildInstrs(LinearIRBlock block) {
+        instrs.addAll(block.getStmts());
+
+        for (var successor : block.getSuccessors()) {
+            buildInstrs(successor);
+        }
+
+    }
+
+    public void optimizeBasicBlock() {
+        for(var func : blockList) {
+            optimizeEmptyBlock(func);
+        }
+
+        for( var emptyBlock : needRemovedBlocks) {
+            emptyBlock.getPredecessors().forEach(p -> p.removeSuccessor(emptyBlock));
+        }
+
+        for(var func : blockList) {
+            insertLabelForBlock(func);
         }
     }
 
@@ -67,8 +108,8 @@ public List<IRNode> linearInstrs() {
             return truncateInstrList;
         }
 
-        for(var block : blockList) {
-            linearInstrsImpl(block);
+        for(var func : blockList) {
+            buildInstrs(func);
         }
 
         IRNode prev;
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/stmt/Label.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/stmt/Label.java
index 423a513..bcfbc84 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/stmt/Label.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/stmt/Label.java
@@ -31,9 +31,7 @@ public Label(Scope scope,Integer ord) {
     }
 
     public Label(Scope scope) {
-        this.scope = scope;
-        this.seq = scope.getLabelSeq();
-        this.rawLabel = null;
+        this(scope, scope.getLabelSeq());
     }
 
     public void setRawLabel(String rawLabel) {
diff --git a/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/stmt/Stmt.java b/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/stmt/Stmt.java
index e3f31e5..e60e12a 100644
--- a/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/stmt/Stmt.java
+++ b/ep20/src/main/java/org/teachfx/antlr4/ep20/ir/stmt/Stmt.java
@@ -15,4 +15,5 @@ public enum StmtType {
     public abstract <S,E> S accept(IRVisitor<S,E> visitor);
 
     public abstract StmtType getStmtType();
+
 }
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 4447db3..df1f689 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
@@ -4,6 +4,9 @@
 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.CJMP;
+import org.teachfx.antlr4.ep20.ir.stmt.FuncEntryLabel;
+import org.teachfx.antlr4.ep20.ir.stmt.JMP;
 import org.teachfx.antlr4.ep20.ir.stmt.Label;
 import org.teachfx.antlr4.ep20.utils.Kind;
 
@@ -25,17 +28,17 @@ public class BasicBlock<I extends IRNode> implements Comparable<BasicBlock<I>>,
     public Set<Operand> liveOut;
     protected Label label;
 
-    public BasicBlock(Kind kind, List<Loc<I>> codes, Label label) {
+    public BasicBlock(Kind kind, List<Loc<I>> codes,Label label,int ord) {
         this.codes = codes;
         this.label = label;
-        this.id = label.getSeq();
+        this.id = ord;
         this.kind = kind;
     }
 
     @NotNull
     @Contract("_ -> new")
-    public static BasicBlock<IRNode> buildFromLinearBlock(@NotNull LinearIRBlock block) {
-        return new BasicBlock<IRNode>(block.getKind(), block.getStmts().stream().map(Loc::new).toList(), block.getLabel());
+    public static BasicBlock<IRNode> buildFromLinearBlock(@NotNull LinearIRBlock block,List<BasicBlock<IRNode>> cachedNodes) {
+        return new BasicBlock<IRNode>(block.getKind(), block.getStmts().stream().map(Loc::new).toList(),block.getLabel(),block.getOrd());
     }
 
     @Override
@@ -93,6 +96,11 @@ public List<Loc<I>> allSeq() {
 
     public List<Loc<I>> dropLabelSeq() {
         if (codes.size() <= 1) return codes;
+
+        if (codes.get(0).instr instanceof FuncEntryLabel) {
+            return codes.subList(0, codes.size());
+        }
+
         return codes.subList(1, codes.size());
     }
 
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 fa1269c..5ad8437 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
@@ -22,15 +22,14 @@ public class CFG<I extends IRNode> implements Iterable<BasicBlock<I>> {
     // index: 第几号节点 ->   <prev,successors> : <前驱节点的集合，后继节点的集合>
     private final List<Pair<Set<Integer>, Set<Integer>>> links;
 
-    public CFG(Map<Integer, BasicBlock<I>> nodes, List<Pair<Integer, Integer>> edges) {
+    public CFG(List<BasicBlock<I>> nodes, List<Pair<Integer, Integer>> edges) {
         // Generate init
-        var lastOrd = Integer.max(nodes.keySet().stream().max(Integer::compareTo).get(), nodes.size()) + 1;
-
-        this.nodes = new LinkedList<>(nodes.values());
+        var maxOrd = nodes.stream().max(BasicBlock::compareTo).map(BasicBlock::getId).get() + 1;
+        this.nodes = nodes;
         this.edges = edges;
 
         links = new ArrayList<>();
-        for (var i = 0; i < lastOrd; i++) {
+        for (var i = 0; i < maxOrd; i++) {
             links.add(Pair.of(new TreeSet<>(), new TreeSet<>()));
         }
 
@@ -78,7 +77,7 @@ public String toString() {
         var graphRenderBuffer = new StringBuilder("graph TD\n");
         AtomicInteger i = new AtomicInteger();
 
-        for (var node : nodes.stream().sorted((b1,b2)-> b2.id - b1.id).toList()) {
+        for (var node : nodes.stream().sorted((b1,b2) -> b2.id - b1.id).toList()) {
 
             graphRenderBuffer.append("subgraph ").append(node.getOrdLabel()).append("\n");
             node.dropLabelSeq().stream().map(x -> x.instr.toString()).map(x -> "Q" + (i.getAndIncrement()) + "[\"" + x + ";\"]\n").forEach(graphRenderBuffer::append);
@@ -87,7 +86,6 @@ public String toString() {
         }
 
         for (var edge : edges) {
-
             graphRenderBuffer.append("L").append(edge.getLeft()).append(" --> ").append("L").append(edge.getRight()).append("\n");
         }
 
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 00d8848..f949619 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
@@ -2,29 +2,62 @@
 
 import org.apache.commons.lang3.tuple.Pair;
 import org.teachfx.antlr4.ep20.ir.IRNode;
+import org.teachfx.antlr4.ep20.ir.JMPInstr;
+import org.teachfx.antlr4.ep20.ir.stmt.CJMP;
+import org.teachfx.antlr4.ep20.ir.stmt.JMP;
 
 import java.util.*;
 
 public class CFGBuilder {
     private static final Set<String> cachedEdgeLinks = new HashSet<>();
     private final CFG<IRNode> cfg;
-    private final Map<Integer, BasicBlock<IRNode>> basicBlocks;
+    private final List<BasicBlock<IRNode>> basicBlocks;
     private final List<Pair<Integer, Integer>> edges;
 
-    public CFGBuilder(List<LinearIRBlock> blockList) {
-        basicBlocks = new HashMap<>();
+    public CFGBuilder(LinearIRBlock startBlock) {
+        basicBlocks = new ArrayList<>();
         edges = new ArrayList<>();
-        for (var funcLabelBlock : blockList) {
-            build(funcLabelBlock);
-        }
+
+        var cachedEdgeLink = new HashSet<String>();
+
+        build(startBlock,cachedEdgeLink);
+
         cfg = new CFG<>(basicBlocks, edges);
     }
 
-    private void build(LinearIRBlock block) {
-        basicBlocks.put(block.getLabel().getSeq(), BasicBlock.buildFromLinearBlock(block));
+    private void build(LinearIRBlock block,Set<String> cachedEdgeLinks) {
+        var currentBlock = BasicBlock.buildFromLinearBlock(block,basicBlocks);
+        basicBlocks.add(currentBlock);
+        var lastInstr = block.getStmts().get(block.getStmts().size() - 1);
+        var currentOrd = block.getOrd();
 
+        if (lastInstr instanceof JMP jmp) {
+            var destOrd = jmp.getNext().getOrd();
+            var key = currentOrd + "-" + destOrd;
+            if (!cachedEdgeLinks.contains(key)) {
+                cachedEdgeLinks.add(key);
+                edges.add(Pair.of(currentOrd, destOrd));
+            }
+        } else if (lastInstr instanceof CJMP cjmp) {
+            var elseOrd = cjmp.getElseBlock().getOrd();
+            var key = currentOrd + "-" + elseOrd;
+            if (!cachedEdgeLinks.contains(key)) {
+                cachedEdgeLinks.add(key);
+                edges.add(Pair.of(currentOrd, elseOrd));
+            }
+        }
+
+        for (var successor : block.getSuccessors()){
+            var key = currentOrd + "-" + successor.getOrd();
+            if (!cachedEdgeLinks.contains(key)) {
+                cachedEdgeLinks.add(key);
+                edges.add(Pair.of(currentOrd, successor.getOrd()));
+            }
+            build(successor,cachedEdgeLinks);
+        }
     }
 
+
     public CFG<IRNode> getCFG() {
         return cfg;
     }
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 e019544..db0b52d 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
@@ -26,14 +26,23 @@ public class LinearIRBlock implements Comparable<LinearIRBlock> {
     private List<JMPInstr> jmpRefMap = new ArrayList<>();
 
     // Constructor
-    public LinearIRBlock() {
+    public LinearIRBlock(Scope scope) {
         stmts = new ArrayList<>();
         successors = new ArrayList<>();
         predecessors = new ArrayList<>();
         ord = LABEL_SEQ++;
+        this.scope = scope;
         logger.info(ord);
     }
 
+    public LinearIRBlock() {
+        stmts = new ArrayList<>();
+        successors = new ArrayList<>();
+        predecessors = new ArrayList<>();
+        ord = LABEL_SEQ++;
+        this.scope = null;
+        logger.info(ord);
+    }
     public static boolean isBasicBlock(Stmt stmt) {
         return !(stmt instanceof CJMP) && !(stmt instanceof JMP);
     }
@@ -51,6 +60,10 @@ public void addStmt(IRNode stmt) {
         updateKindByLastInstr(stmt);
     }
 
+    public void insertStmt(IRNode stmt,int idx) {
+        stmts.add(idx, stmt);
+    }
+
     private void updateKindByLastInstr(IRNode stmt) {
         if (stmt instanceof CJMP) {
             kind = Kind.END_BY_CJMP;
@@ -152,14 +165,10 @@ public Label getLabel() {
 
         var firstInstr = stmts.get(0);
         if (firstInstr instanceof Label label) {
-
             return label;
-        } else {
-            stmts.add(0, new Label(scope, getOrd()));
-            firstInstr = stmts.get(0);
         }
 
-        return (Label) firstInstr;
+        return null;
     }
 
     public Optional<TreeSet<LinearIRBlock>> getJumpEntries() {
@@ -201,12 +210,16 @@ public int hashCode() {
      */
     public void mergeBlock(LinearIRBlock otherBlock) {
         stmts.addAll(otherBlock.getStmts());
+
         updateKindByLastInstr(stmts.get(stmts.size() - 1));
+
         setSuccessors(otherBlock.getSuccessors());
+
         for(var s : otherBlock.getSuccessors()) {
             s.predecessors.remove(otherBlock);
             s.predecessors.add(this);
         }
+
         for (var jmp : otherBlock.getJmpRefMap()) {
             if (jmp instanceof JMP jmpInstr) {
                 jmpInstr.setNext(this);
@@ -217,4 +230,8 @@ public void mergeBlock(LinearIRBlock otherBlock) {
             }
         }
     }
+
+    public void removeSuccessor(LinearIRBlock block) {
+        successors.remove(block);
+    }
 }
\ No newline at end of file
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 0b655ff..d95c7e7 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
@@ -75,6 +75,8 @@ public Void visit(Label label) {
         if (indents > 0) { indents--; }
 
         if (label instanceof FuncEntryLabel){
+            // reset indent
+            indents = 0;
             emit("%s".formatted(label.toSource()));
         } else {
             emit("%s:".formatted(label.toSource()));
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 7d13b1d..cf6f4fb 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
@@ -230,9 +230,9 @@ public Void visit(ReturnStmtNode returnStmtNode) {
     @Override
     public Void visit(WhileStmtNode whileStmtNode) {
         curNode = whileStmtNode;
-        var condBlock = new LinearIRBlock();
-        var doBlock = new LinearIRBlock();
-        var endBlock = new LinearIRBlock();
+        var condBlock = new LinearIRBlock(currentBlock.getScope());
+        var doBlock = new LinearIRBlock(currentBlock.getScope());
+        var endBlock = new LinearIRBlock(currentBlock.getScope());
 
         jump(condBlock);
 
@@ -263,15 +263,15 @@ public Void visit(IfStmtNode ifStmtNode) {
 
         ifStmtNode.getCondExpr().accept(this);
         var cond = peekEvalOperand();
-        var thenBlock = new LinearIRBlock();
-        var endBlock = new LinearIRBlock();
+        var thenBlock = new LinearIRBlock(currentBlock.getScope());
+        var endBlock = new LinearIRBlock(currentBlock.getScope());
 
         if (ifStmtNode.getElseBlock().isEmpty()) {
             jumpIf(cond,thenBlock,endBlock);
             setCurrentBlock(thenBlock);
             ifStmtNode.getThenBlock().accept(this);
         }else {
-            var elseBlock = new LinearIRBlock();
+            var elseBlock = new LinearIRBlock(currentBlock.getScope());
             jumpIf(cond,thenBlock,elseBlock);
             setCurrentBlock(thenBlock);
             ifStmtNode.getThenBlock().accept(this);
@@ -426,20 +426,8 @@ protected VarSlot peekEvalOperand() {
         return evalExprStack.peek();
     }
 
-    public CFG<IRNode> getCFG(List<LinearIRBlock> blocks) {
-        for (var func : blocks){
-            insertBlockLabel(func);
-        }
-
-        var cfgBuilder = new CFGBuilder(blocks);
+    public CFG<IRNode> getCFG(LinearIRBlock startBlocks) {
+        var cfgBuilder = new CFGBuilder(startBlocks);
         return cfgBuilder.getCFG();
     }
-
-    public void insertBlockLabel(LinearIRBlock startBlock) {
-        startBlock.getLabel();
-
-        for (var successor : startBlock.getSuccessors()) {
-            insertBlockLabel(successor);
-        }
-    }
 }