diff --git a/src/bin/jbc2mpl b/src/bin/jbc2mpl
index cda7ba6d4877991ece9166593edc8e5aaeafbf5e..ed11e3a0b6ea16dcd537ab18b3256e8ef71fdda8 100755
Binary files a/src/bin/jbc2mpl and b/src/bin/jbc2mpl differ
diff --git a/src/bin/maple b/src/bin/maple
index 7c64c05eacea21dce23efacac0cfb0482a9afc63..146010e30c1c80f697f8c7ad8c5797742d7b2e55 100755
Binary files a/src/bin/maple and b/src/bin/maple differ
diff --git a/src/maple_driver/defs/supported_compilers.def b/src/maple_driver/defs/supported_compilers.def
deleted file mode 100644
index a224fe6500dde8884a05e592ab013a7aef805299..0000000000000000000000000000000000000000
--- a/src/maple_driver/defs/supported_compilers.def
+++ /dev/null
@@ -1,18 +0,0 @@
-/*
- * Copyright (c) [2019] Huawei Technologies Co.,Ltd.All rights reserved.
- *
- * OpenArkCompiler is licensed under the Mulan PSL v1.
- * You can use this software according to the terms and conditions of the Mulan PSL v1.
- * You may obtain a copy of Mulan PSL v1 at:
- *
- *     http://license.coscl.org.cn/MulanPSL
- *
- * THIS SOFTWARE IS PROVIDED ON AN "AS IS" BASIS, WITHOUT WARRANTIES OF ANY KIND, EITHER
- * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO NON-INFRINGEMENT, MERCHANTABILITY OR
- * FIT FOR A PARTICULAR PURPOSE.
- * See the Mulan PSL v1 for more details.
- */
-ADD_COMPILER("jbc2mpl" ,Jbc2MplCompiler)
-ADD_COMPILER("me" ,MapleCombCompiler)
-ADD_COMPILER("mpl2mpl" ,MapleCombCompiler)
-ADD_COMPILER("mplcg" ,MplcgCompiler)
diff --git a/src/maple_driver/include/compiler.h b/src/maple_driver/include/compiler.h
index e2cefeafe3c2a4042db181f630c041ac43df81eb..3e392f5587112a9d0867f42e73aa5a0f7ad7de2c 100644
--- a/src/maple_driver/include/compiler.h
+++ b/src/maple_driver/include/compiler.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) [2019] Huawei Technologies Co.,Ltd.All rights reserved.
+ * Copyright (c) [2019-2020] Huawei Technologies Co.,Ltd.All rights reserved.
  *
  * OpenArkCompiler is licensed under the Mulan PSL v1.
  * You can use this software according to the terms and conditions of the Mulan PSL v1.
@@ -24,11 +24,12 @@
 #include "mir_parser.h"
 
 namespace maple {
-extern const std::string kBinNameJbc2mpl;
-extern const std::string kBinNameMe;
-extern const std::string kBinNameMpl2mpl;
-extern const std::string kBinNameMplcg;
-extern const std::string kBinNameMapleComb;
+const std::string kBinNameNone = "";
+const std::string kBinNameJbc2mpl = "jbc2mpl";
+const std::string kBinNameMe = "me";
+const std::string kBinNameMpl2mpl = "mpl2mpl";
+const std::string kBinNameMplcg = "mplcg";
+const std::string kBinNameMapleComb = "maplecomb";
 
 class Compiler {
  public:
@@ -48,8 +49,8 @@ class Compiler {
 
  protected:
   virtual std::string GetBinPath(const MplOptions &mplOptions) const;
-  virtual std::string GetBinName() const {
-    return "";
+  virtual const std::string &GetBinName() const {
+    return kBinNameNone;
   }
 
   virtual std::string GetInputFileName(const MplOptions &options) const {
@@ -70,10 +71,6 @@ class Compiler {
 
   virtual std::string AppendOptimization(const MplOptions &options, const std::string &optionStr) const;
 
-  virtual std::vector<std::string> GetBinNames() const {
-    return std::vector<std::string>();
-  }
-
   bool CanAppendOptimization() const;
 
  private:
@@ -101,11 +98,10 @@ class Jbc2MplCompiler : public Compiler {
   ~Jbc2MplCompiler() = default;
 
  private:
-  std::string GetBinName() const override;
+  const std::string &GetBinName() const override;
   DefaultOption GetDefaultOptions(const MplOptions &options) const override;
   void GetTmpFilesToDelete(const MplOptions &mplOptions, std::vector<std::string> &tempFiles) const override;
   std::unordered_set<std::string> GetFinalOutputs(const MplOptions &mplOptions) const override;
-  std::vector<std::string> GetBinNames() const override;
 };
 
 class MapleCombCompiler : public Compiler {
@@ -133,8 +129,7 @@ class MplcgCompiler : public Compiler {
  private:
   std::string GetInputFileName(const MplOptions &options) const override;
   DefaultOption GetDefaultOptions(const MplOptions &options) const override;
-  std::string GetBinName() const override;
-  std::vector<std::string> GetBinNames() const override;
+  const std::string &GetBinName() const override;
 };
 }  // namespace maple
 #endif  // MAPLE_DRIVER_INCLUDE_COMPILER_H
diff --git a/src/maple_driver/include/option_parser.h b/src/maple_driver/include/option_parser.h
index f228412da855bbb834ab01fe295a6a52b567ccfe..03dece32e57e03317a018073140b6d8bd08e9f5f 100644
--- a/src/maple_driver/include/option_parser.h
+++ b/src/maple_driver/include/option_parser.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) [2019-2020] Huawei Technologies Co.,Ltd.All rights reserved.
+ * Copyright (c) [2020] Huawei Technologies Co.,Ltd.All rights reserved.
  *
  * OpenArkCompiler is licensed under the Mulan PSL v1.
  * You can use this software according to the terms and conditions of the Mulan PSL v1.
@@ -228,6 +228,11 @@ class OptionParser {
   std::vector<Option> options;
   std::vector<std::string> nonOptionsArgs;
 };
+enum MatchedIndex {
+  kMatchNone,
+  kMatchShortOpt,
+  kMatchLongOpt
+};
 }  // namespace mapleOption
 
 #endif  // MAPLE_UTIL_INCLUDE_OPTION_PARSER_H
diff --git a/src/maple_driver/include/safe_exe.h b/src/maple_driver/include/safe_exe.h
index 0f0532e2139240bcbe0e33c228d8466abdb1e3ab..bc512341fd409c8b15a92e9d69c901a997c8f403 100644
--- a/src/maple_driver/include/safe_exe.h
+++ b/src/maple_driver/include/safe_exe.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) [2019] Huawei Technologies Co.,Ltd.All rights reserved.
+ * Copyright (c) [2019-2020] Huawei Technologies Co.,Ltd.All rights reserved.
  *
  * OpenArkCompiler is licensed under the Mulan PSL v1.
  * You can use this software according to the terms and conditions of the Mulan PSL v1.
diff --git a/src/maple_driver/include/usages.h b/src/maple_driver/include/usages.h
index 2f2dbccfd794cfaac4cd68dc963c9f80c6b33acb..85da21f5f7b2467be4ecaf87a8a5f40ee39448a3 100644
--- a/src/maple_driver/include/usages.h
+++ b/src/maple_driver/include/usages.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) [2019] Huawei Technologies Co.,Ltd.All rights reserved.
+ * Copyright (c) [2019-2020] Huawei Technologies Co.,Ltd.All rights reserved.
  *
  * OpenArkCompiler is licensed under the Mulan PSL v1.
  * You can use this software according to the terms and conditions of the Mulan PSL v1.
@@ -32,8 +32,7 @@ enum OptionIndex : uint64 {
   // ----------jbc2mpl begin-------
   kUseStringFactory,
   kJbc2mplOutMpl,
-  // -------- comb begin-------- --
-  kCombTimePhases,
+  kTimePhases,
   kGenMeMpl,
   kGenVtableImpl,
   kVerify,
diff --git a/src/maple_driver/src/compiler.cpp b/src/maple_driver/src/compiler.cpp
index 3ea6b5d93b628e87d978ff604e6a7d763fa5be95..72d09f00ddd5ce9fff11ae52db9f9d94a97e3aac 100644
--- a/src/maple_driver/src/compiler.cpp
+++ b/src/maple_driver/src/compiler.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) [2019] Huawei Technologies Co.,Ltd.All rights reserved.
+ * Copyright (c) [2019-2020] Huawei Technologies Co.,Ltd.All rights reserved.
  *
  * OpenArkCompiler is licensed under the Mulan PSL v1.
  * You can use this software according to the terms and conditions of the Mulan PSL v1.
@@ -21,12 +21,6 @@
 namespace maple {
 using namespace mapleOption;
 
-const std::string kBinNameJbc2mpl = "jbc2mpl";
-const std::string kBinNameMe = "me";
-const std::string kBinNameMpl2mpl = "mpl2mpl";
-const std::string kBinNameMplcg = "mplcg";
-const std::string kBinNameMapleComb = "maplecomb";
-
 int Compiler::Exe(const MplOptions &mplOptions, const std::string &options) const {
   std::ostringstream ostrStream;
   ostrStream << GetBinPath(mplOptions) << GetBinName();
@@ -68,11 +62,9 @@ std::string Compiler::MakeOption(const MplOptions &options) const {
   std::map<std::string, MplOption> finalOptions;
   std::map<std::string, MplOption> defaultOptions = MakeDefaultOptions(options);
   AppendDefaultOptions(finalOptions, defaultOptions);
-  for (const auto &binName : GetBinNames()) {
-    auto userOption = options.GetOptions().find(binName);
-    if (userOption != options.GetOptions().end()) {
-      AppendUserOptions(finalOptions, userOption->second);
-    }
+  auto userOption = options.GetOptions().find(GetBinName());
+  if (userOption != options.GetOptions().end()) {
+    AppendUserOptions(finalOptions, userOption->second);
   }
   AppendExtraOptions(finalOptions, options.GetExtras());
   std::ostringstream strOption;
@@ -99,27 +91,24 @@ void Compiler::AppendDefaultOptions(std::map<std::string, MplOption> &finalOptio
 
 void Compiler::AppendUserOptions(std::map<std::string, MplOption> &finalOptions,
                                  const std::vector<Option> &userOptions) const {
-  for (const auto &binName : GetBinNames()) {
-    for (const auto &userOption : userOptions) {
-      auto extra = userOption.FindExtra(binName);
-      if (extra != nullptr) {
-        AppendOptions(finalOptions, extra->optionKey, userOption.Args(), userOption.ConnectSymbol(binName));
-      }
+  const std::string &binName = GetBinName();
+  for (const auto &userOption : userOptions) {
+    auto extra = userOption.FindExtra(binName);
+    if (extra != nullptr) {
+      AppendOptions(finalOptions, extra->optionKey, userOption.Args(), userOption.ConnectSymbol(binName));
     }
   }
 }
 
 void Compiler::AppendExtraOptions(std::map<std::string, MplOption> &finalOptions,
                                   const std::map<std::string, std::vector<MplOption>> &extraOptions) const {
-  auto binNames = GetBinNames();
-  for (const auto &binNamesIt : binNames) {
-    auto extras = extraOptions.find(binNamesIt);
-    if (extras == extraOptions.end()) {
-      continue;
-    }
-    for (const auto &secondExtras : extras->second) {
-      AppendOptions(finalOptions, secondExtras.GetKey(), secondExtras.GetValue(), secondExtras.GetconnectSymbol());
-    }
+  const std::string &binName = GetBinName();
+  auto extras = extraOptions.find(binName);
+  if (extras == extraOptions.end()) {
+    return;
+  }
+  for (const auto &secondExtras : extras->second) {
+    AppendOptions(finalOptions, secondExtras.GetKey(), secondExtras.GetValue(), secondExtras.GetconnectSymbol());
   }
 }
 
diff --git a/src/maple_driver/src/driver_runner.cpp b/src/maple_driver/src/driver_runner.cpp
index 4fe26232cef31ab21ebea03f311e83925a28f83a..0f82d396a34f18aaf4392095f56bfd413f324399 100644
--- a/src/maple_driver/src/driver_runner.cpp
+++ b/src/maple_driver/src/driver_runner.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) [2019] Huawei Technologies Co.,Ltd.All rights reserved.
+ * Copyright (c) [2019-2020] Huawei Technologies Co.,Ltd.All rights reserved.
  *
  * OpenArkCompiler is licensed under the Mulan PSL v1.
  * You can use this software according to the terms and conditions of the Mulan PSL v1.
@@ -52,8 +52,8 @@
   }
 
 namespace maple {
-const std::string mpl2Mpl = "mpl2mpl";
-const std::string mplME = "me";
+const std::string kMpl2mpl = "mpl2mpl";
+const std::string kMplMe = "me";
 
 enum OptLevel {
   kLevelO0,
@@ -99,10 +99,10 @@ bool DriverRunner::IsFramework() const {
 }
 
 std::string DriverRunner::GetPostfix() const {
-  if (printOutExe == mplME) {
+  if (printOutExe == kMplMe) {
     return ".me.mpl";
   }
-  if (printOutExe == mpl2Mpl) {
+  if (printOutExe == kMpl2mpl) {
     return ".VtableImpl.mpl";
   }
   return "";
@@ -143,7 +143,7 @@ void DriverRunner::ProcessMpl2mplAndMePhases(const std::string &outputFile, cons
     mgr.Run();
 
     // emit after module phase
-    if (printOutExe == mpl2Mpl || printOutExe == mplME) {
+    if (printOutExe == kMpl2mpl || printOutExe == kMplMe) {
       theModule->Emit(outputFile);
     } else if (genVtableImpl || Options::emitVtableImpl) {
       theModule->Emit(vtableImplFile);
diff --git a/src/maple_driver/src/jbc2mpl_compiler.cpp b/src/maple_driver/src/jbc2mpl_compiler.cpp
index 6117688bd50b1a64ccf225f25432369db481996f..ddb9488f50ba883456e8fb03ce82b409d3c091e9 100644
--- a/src/maple_driver/src/jbc2mpl_compiler.cpp
+++ b/src/maple_driver/src/jbc2mpl_compiler.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) [2019] Huawei Technologies Co.,Ltd.All rights reserved.
+ * Copyright (c) [2019-2020] Huawei Technologies Co.,Ltd.All rights reserved.
  *
  * OpenArkCompiler is licensed under the Mulan PSL v1.
  * You can use this software according to the terms and conditions of the Mulan PSL v1.
@@ -17,14 +17,10 @@
 #include "default_options.def"
 
 namespace maple {
-std::string Jbc2MplCompiler::GetBinName() const {
+const std::string &Jbc2MplCompiler::GetBinName() const {
   return kBinNameJbc2mpl;
 }
 
-std::vector<std::string> Jbc2MplCompiler::GetBinNames() const {
-  return std::vector<std::string> { kBinNameJbc2mpl };
-}
-
 DefaultOption Jbc2MplCompiler::GetDefaultOptions(const MplOptions &options) const {
   DefaultOption defaultOptions = { nullptr, 0 };
   return defaultOptions;
diff --git a/src/maple_driver/src/maple_comb_compiler.cpp b/src/maple_driver/src/maple_comb_compiler.cpp
index 4814de4aa4922f72e67ad220cb0b4672043b0ec0..04ceb8c8d153e84b4b54b17aa0db8248297e4d36 100644
--- a/src/maple_driver/src/maple_comb_compiler.cpp
+++ b/src/maple_driver/src/maple_comb_compiler.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) [2019] Huawei Technologies Co.,Ltd.All rights reserved.
+ * Copyright (c) [2019-2020] Huawei Technologies Co.,Ltd.All rights reserved.
  *
  * OpenArkCompiler is licensed under the Mulan PSL v1.
  * You can use this software according to the terms and conditions of the Mulan PSL v1.
diff --git a/src/maple_driver/src/mpl_options.cpp b/src/maple_driver/src/mpl_options.cpp
index d00d5959f09b9cdcdb845378a7c6790ab17cb8e4..c9f3e9434c8b2cf4437ae475c9a5977b909448ae 100644
--- a/src/maple_driver/src/mpl_options.cpp
+++ b/src/maple_driver/src/mpl_options.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) [2019] Huawei Technologies Co.,Ltd.All rights reserved.
+ * Copyright (c) [2019-2020] Huawei Technologies Co.,Ltd.All rights reserved.
  *
  * OpenArkCompiler is licensed under the Mulan PSL v1.
  * You can use this software according to the terms and conditions of the Mulan PSL v1.
@@ -175,7 +175,7 @@ const mapleOption::Descriptor USAGES[] = {
     "                              \t--run.\n",
     "all",
     { { nullptr } } },
-  { kCombTimePhases,
+  { kTimePhases,
     0,
     "time-phases",
     nullptr,
@@ -1074,7 +1074,7 @@ ErrorCode MplOptions::HandleGeneralOptions() {
       case kMpl2MplHelp:
         optionParser->PrintUsage(kBinNameMpl2mpl);
         return kErrorExitHelp;
-      case kCombTimePhases:
+      case kTimePhases:
         timePhases = true;
         printCommandStr += " -time-phases";
         break;
diff --git a/src/maple_driver/src/mplcg_compiler.cpp b/src/maple_driver/src/mplcg_compiler.cpp
index 497a34eacb18f4d26384fa4639dfc66c11e99994..09b63d2b6bfaf35c1415a26ca45ec22722b1d90f 100644
--- a/src/maple_driver/src/mplcg_compiler.cpp
+++ b/src/maple_driver/src/mplcg_compiler.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) [2019] Huawei Technologies Co.,Ltd.All rights reserved.
+ * Copyright (c) [2019-2020] Huawei Technologies Co.,Ltd.All rights reserved.
  *
  * OpenArkCompiler is licensed under the Mulan PSL v1.
  * You can use this software according to the terms and conditions of the Mulan PSL v1.
@@ -31,15 +31,10 @@ DefaultOption MplcgCompiler::GetDefaultOptions(const MplOptions &options) const
   return defaultOptions;
 }
 
-std::string MplcgCompiler::GetBinName() const {
+const std::string &MplcgCompiler::GetBinName() const {
   return kBinNameMplcg;
 }
 
-std::vector<std::string> MplcgCompiler::GetBinNames() const {
-  std::vector<std::string> binNames{ kBinNameMplcg };
-  return binNames;
-}
-
 std::string MplcgCompiler::GetInputFileName(const MplOptions &options) const {
   if (!options.GetRunningExes().empty()) {
     if (options.GetRunningExes()[0] == kBinNameMplcg) {
diff --git a/src/maple_driver/src/option_parser.cpp b/src/maple_driver/src/option_parser.cpp
index b639a8f6a72b4d1d57cb40ec7092cb7debb33333..735ca4de2117746dea08d60c5a9980e2e7854076 100644
--- a/src/maple_driver/src/option_parser.cpp
+++ b/src/maple_driver/src/option_parser.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) [2019-2020] Huawei Technologies Co.,Ltd.All rights reserved.
+ * Copyright (c) [2020] Huawei Technologies Co.,Ltd.All rights reserved.
  *
  * OpenArkCompiler is licensed under the Mulan PSL v1.
  * You can use this software according to the terms and conditions of the Mulan PSL v1.
@@ -62,7 +62,7 @@ bool OptionParser::HandleKeyValue(const std::string &key, const std::string &val
     nonOptionsArgs.push_back(value);
     return true;
   }
-  int count = usages.count(key);
+  size_t count = usages.count(key);
   auto item = usages.find(key);
 #ifdef OPTION_PARSER_EXTRAOPT
   while (count > 0 && item->second.exeName != exeName) {
@@ -191,16 +191,16 @@ ErrorCode OptionParser::HandleInputArgs(const std::vector<std::string> &inputArg
     }
     bool isMatchLongOpt = false;
     bool isMatchShortOpt = false;
-    int index = 0;
+    MatchedIndex index = kMatchNone;
     if (inputArgs[i][0] == '-') {
-      index = 1;
+      index = kMatchShortOpt;
       if (inputArgs[i][1] == '-') {
-        index = 2;
+        index = kMatchLongOpt;
       }
     }
-    if (index == 1) {
+    if (index == kMatchShortOpt) {
       isMatchShortOpt = true;
-    } else if (index == 2) {
+    } else if (index == kMatchLongOpt) {
       isMatchLongOpt = true;
     }
     std::string arg = inputArgs[i].substr(index);
diff --git a/src/maple_me/include/irmap.h b/src/maple_me/include/irmap.h
index 49da7f158c75cc8b2ca08f757b7e5269a90904b9..c47e3a95042b79fcc0aec1efe25f5c7933b10a27 100644
--- a/src/maple_me/include/irmap.h
+++ b/src/maple_me/include/irmap.h
@@ -186,7 +186,7 @@ class IRMap : public AnalysisResult {
   uint32 mapHashLength;                            // size of hashTable
   MapleVector<MeExpr*> hashTable;                  // the value number hash table
   MapleVector<MeExpr*> vst2MeExprTable;            // map versionst to MeExpr.
-  MapleVector<RegMeExpr*> regMeExprTable;          // record all the regmeexpr created by ssapre
+  MapleVector<RegMeExpr*> regMeExprTable;          // record all the regmeexpr created by ssa_pre
   bool needAnotherPass = false;                    // set to true if CFG has changed
   bool dumpStmtNum = false;
   BB *curBB = nullptr;  // current maple_me::BB being visited
diff --git a/src/maple_me/include/me_bb_layout.h b/src/maple_me/include/me_bb_layout.h
index 9bff241ca47c92ce8f55ec78ed3c7fa1eeb77bed..8ec4d491c70d4962c7b3aabef870e9f250d982f6 100644
--- a/src/maple_me/include/me_bb_layout.h
+++ b/src/maple_me/include/me_bb_layout.h
@@ -55,6 +55,7 @@ class BBLayout : public AnalysisResult {
   BB *GetFallThruBBSkippingEmpty(BB &bb);
   void ResolveUnconditionalFallThru(BB &bb, BB &nextBB);
   void ChangeToFallthruFromGoto(BB &bb);
+  void RemoveUnreachable(BB &bb);
   const MapleVector<BB*> &GetBBs() const {
     return layoutBBs;
   }
diff --git a/src/maple_me/src/me_bb_layout.cpp b/src/maple_me/src/me_bb_layout.cpp
index 55160612bc9e679df04f8d24a589bec5e41408db..bc219fb99eed975c1c63106f7b2d4f61bf55a7cf 100644
--- a/src/maple_me/src/me_bb_layout.cpp
+++ b/src/maple_me/src/me_bb_layout.cpp
@@ -276,10 +276,9 @@ void BBLayout::OptimizeBranchTarget(BB &bb) {
     // update CFG
     bb.ReplaceSucc(brTargetBB, newTargetBB);
     bb.RemoveBBFromVector(brTargetBB->GetPred());
-    if (brTargetBB->GetPred().empty() && !laidOut[brTargetBB->GetBBId()]) {
+    if (brTargetBB->GetPred().empty()) {
       laidOut[brTargetBB->GetBBId()] = true;
-      brTargetBB->RemoveBBFromVector(newTargetBB->GetPred());
-      func.NullifyBBByID(brTargetBB->GetBBId());
+      RemoveUnreachable(*brTargetBB);
     }
   } while (true);
 }
@@ -334,11 +333,13 @@ BB *BBLayout::GetFallThruBBSkippingEmpty(BB &bb) {
       }
     }
     laidOut[fallthru->GetBBId()] = true;
-    fallthru->RemoveBBFromPred(&bb);
-    BB *oldFallthru = fallthru;
-    fallthru = oldFallthru->GetSucc().front();
-    bb.ReplaceSucc(oldFallthru, fallthru);
-    oldFallthru->RemoveBBFromSucc(fallthru);
+    BB *oldFallThru = fallthru;
+    fallthru = fallthru->GetSucc().front();
+    bb.ReplaceSucc(oldFallThru, fallthru);
+    oldFallThru->RemoveBBFromPred(&bb);
+    if (oldFallThru->GetPred().empty()) {
+      RemoveUnreachable(*oldFallThru);
+    }
   } while (true);
 }
 
@@ -376,6 +377,24 @@ void BBLayout::ResolveUnconditionalFallThru(BB &bb, BB &nextBB) {
   }
 }
 
+// remove unnessary bb whose pred size is zero
+// keep cfg correct to rebuild dominance
+void BBLayout::RemoveUnreachable(BB &bb) {
+  if (bb.GetAttributes(kBBAttrIsEntry)) {
+    return;
+  }
+  MapleVector<BB*> succBBs = bb.GetSucc();
+  for (BB *succ : succBBs) {
+    MapleVector<BB*> preds = succ->GetPred();
+    bb.RemoveBBFromVector(preds);
+    if (preds.empty()) {
+        RemoveUnreachable(*succ);
+    }
+  }
+  succBBs.clear();
+  func.NullifyBBByID(bb.GetBBId());
+}
+
 AnalysisResult *MeDoBBLayout::Run(MeFunction *func, MeFuncResultMgr *funcResMgr, ModuleResultMgr *moduleResMgr) {
   // mempool used in analysisresult
   MemPool *layoutMp = NewMemPool();
@@ -409,9 +428,11 @@ AnalysisResult *MeDoBBLayout::Run(MeFunction *func, MeFuncResultMgr *funcResMgr,
     if (bb->GetKind() == kBBFallthru) {
       bbLayout->ResolveUnconditionalFallThru(*bb, *nextBB);
     } else if (bb->GetKind() == kBBCondGoto) {
+      BB *oldFallThru = bb->GetSucc(0);
       BB *fallthru = bbLayout->GetFallThruBBSkippingEmpty(*bb);
       BB *brTargetBB = bb->GetSucc(1);
-      if (brTargetBB != fallthru && fallthru->GetPred().size() > 1 && bbLayout->BBCanBeMoved(*brTargetBB, *bb)) {
+      if (brTargetBB != fallthru && (oldFallThru != fallthru || fallthru->GetPred().size() > 1) &&
+          bbLayout->BBCanBeMoved(*brTargetBB, *bb)) {
         // flip the sense of the condgoto and lay out brTargetBB right here
         LabelIdx fallthruLabel = func->GetOrCreateBBLabel(*fallthru);
         if (func->GetIRMap() != nullptr) {
@@ -456,8 +477,6 @@ AnalysisResult *MeDoBBLayout::Run(MeFunction *func, MeFuncResultMgr *funcResMgr,
           // replace pred and succ
           bb->ReplaceSucc(fallthru, newFallthru);
           fallthru->ReplacePred(bb, newFallthru);
-          newFallthru->GetPred().push_back(bb);
-          newFallthru->GetSucc().push_back(fallthru);
           newFallthru->SetFrequency(fallthru->GetFrequency());
           if (DEBUGFUNC(func)) {
             LogInfo::MapleLogger() << "Created fallthru and goto original fallthru" << '\n';