diff --git a/llvm/utils/TableGen/CMakeLists.txt b/llvm/utils/TableGen/CMakeLists.txt
--- a/llvm/utils/TableGen/CMakeLists.txt
+++ b/llvm/utils/TableGen/CMakeLists.txt
@@ -22,13 +22,13 @@
   DAGISelMatcherGen.cpp
   DAGISelMatcherOpt.cpp
   DAGISelMatcher.cpp
+  DecoderEmitter.cpp
   DFAEmitter.cpp
   DFAPacketizerEmitter.cpp
   DirectiveEmitter.cpp
   DisassemblerEmitter.cpp
   ExegesisEmitter.cpp
   FastISelEmitter.cpp
-  FixedLenDecoderEmitter.cpp
   GICombinerEmitter.cpp
   GlobalISelEmitter.cpp
   InfoByHwMode.cpp
diff --git a/llvm/utils/TableGen/FixedLenDecoderEmitter.cpp b/llvm/utils/TableGen/DecoderEmitter.cpp
rename from llvm/utils/TableGen/FixedLenDecoderEmitter.cpp
rename to llvm/utils/TableGen/DecoderEmitter.cpp
--- a/llvm/utils/TableGen/FixedLenDecoderEmitter.cpp
+++ b/llvm/utils/TableGen/DecoderEmitter.cpp
@@ -1,4 +1,4 @@
-//===------------ FixedLenDecoderEmitter.cpp - Decoder Generator ----------===//
+//===------------ DecoderEmitter.cpp - Decoder Generator ----------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 //
 // It contains the tablegen backend that emits the decoder functions for
-// targets with fixed length instruction set.
+// targets with fixed/variable length instruction set.
 //
 //===----------------------------------------------------------------------===//
 
@@ -122,14 +122,14 @@
   return OS;
 }
 
-class FixedLenDecoderEmitter {
+class DecoderEmitter {
   RecordKeeper &RK;
   std::vector<EncodingAndInst> NumberedEncodings;
 
 public:
   // Defaults preserved here for documentation, even though they aren't
   // strictly necessary given the way that this is currently being called.
-  FixedLenDecoderEmitter(RecordKeeper &R, std::string PredicateNamespace,
+  DecoderEmitter(RecordKeeper &R, std::string PredicateNamespace,
                          std::string GPrefix = "if (",
                          std::string GPostfix = " == MCDisassembler::Fail)",
                          std::string ROK = "MCDisassembler::Success",
@@ -411,13 +411,13 @@
   unsigned BitWidth;
 
   // Parent emitter
-  const FixedLenDecoderEmitter *Emitter;
+  const DecoderEmitter *Emitter;
 
 public:
   FilterChooser(ArrayRef<EncodingAndInst> Insts,
                 const std::vector<EncodingIDAndOpcode> &IDs,
                 const std::map<unsigned, std::vector<OperandInfo>> &Ops,
-                unsigned BW, const FixedLenDecoderEmitter *E)
+                unsigned BW, const DecoderEmitter *E)
       : AllInstructions(Insts), Opcodes(IDs), Operands(Ops),
         FilterBitValues(BW, BIT_UNFILTERED), Parent(nullptr), BestIndex(-1),
         BitWidth(BW), Emitter(E) {
@@ -771,7 +771,7 @@
 //////////////////////////////////
 
 // Emit the decoder state machine table.
-void FixedLenDecoderEmitter::emitTable(formatted_raw_ostream &OS,
+void DecoderEmitter::emitTable(formatted_raw_ostream &OS,
                                        DecoderTable &Table,
                                        unsigned Indentation,
                                        unsigned BitWidth,
@@ -960,7 +960,7 @@
   OS.indent(Indentation) << "};\n\n";
 }
 
-void FixedLenDecoderEmitter::emitInstrLenTable(
+void DecoderEmitter::emitInstrLenTable(
     formatted_raw_ostream &OS, std::vector<unsigned> &InstrLen) const {
   OS << "static const uint8_t InstrLenTable[] = {\n";
   for (unsigned &Len : InstrLen) {
@@ -969,7 +969,7 @@
   OS << "};\n\n";
 }
 
-void FixedLenDecoderEmitter::
+void DecoderEmitter::
 emitPredicateFunction(formatted_raw_ostream &OS, PredicateSet &Predicates,
                       unsigned Indentation) const {
   // The predicate function is just a big switch statement based on the
@@ -994,7 +994,7 @@
   OS.indent(Indentation) << "}\n\n";
 }
 
-void FixedLenDecoderEmitter::
+void DecoderEmitter::
 emitDecoderFunction(formatted_raw_ostream &OS, DecoderSet &Decoders,
                     unsigned Indentation) const {
   // The decoder function is just a big switch statement based on the
@@ -2518,7 +2518,7 @@
 }
 
 // Emits disassembler code for instruction decoding.
-void FixedLenDecoderEmitter::run(raw_ostream &o) {
+void DecoderEmitter::run(raw_ostream &o) {
   formatted_raw_ostream OS(o);
   OS << "#include \"llvm/MC/MCInst.h\"\n";
   OS << "#include \"llvm/MC/MCSubtargetInfo.h\"\n";
@@ -2690,12 +2690,12 @@
 
 namespace llvm {
 
-void EmitFixedLenDecoder(RecordKeeper &RK, raw_ostream &OS,
+void EmitDecoder(RecordKeeper &RK, raw_ostream &OS,
                          const std::string &PredicateNamespace,
                          const std::string &GPrefix,
                          const std::string &GPostfix, const std::string &ROK,
                          const std::string &RFail, const std::string &L) {
-  FixedLenDecoderEmitter(RK, PredicateNamespace, GPrefix, GPostfix,
+  DecoderEmitter(RK, PredicateNamespace, GPrefix, GPostfix,
                          ROK, RFail, L).run(OS);
 }
 
diff --git a/llvm/utils/TableGen/DisassemblerEmitter.cpp b/llvm/utils/TableGen/DisassemblerEmitter.cpp
--- a/llvm/utils/TableGen/DisassemblerEmitter.cpp
+++ b/llvm/utils/TableGen/DisassemblerEmitter.cpp
@@ -95,7 +95,7 @@
 
 namespace llvm {
 
-extern void EmitFixedLenDecoder(RecordKeeper &RK, raw_ostream &OS,
+extern void EmitDecoder(RecordKeeper &RK, raw_ostream &OS,
                                 const std::string &PredicateNamespace,
                                 const std::string &GPrefix,
                                 const std::string &GPostfix,
@@ -125,9 +125,9 @@
     return;
   }
 
-  // WebAssembly has variable length opcodes, so can't use EmitFixedLenDecoder
-  // below (which depends on a Size table-gen Record), and also uses a custom
-  // disassembler.
+  // TODO: Since now the original decoder emitter is able to emit decoder for
+  //       variable length opcode, we might have to migrate webassembly to use
+  //       that.
   if (Target.getName() == "WebAssembly") {
     emitWebAssemblyDisassemblerTables(OS, Target.getInstructionsByEnumValue());
     return;
@@ -140,7 +140,7 @@
     if (PredicateNamespace == "Thumb")
       PredicateNamespace = "ARM";
 
-    EmitFixedLenDecoder(Records, OS, PredicateNamespace,
+    EmitDecoder(Records, OS, PredicateNamespace,
                         "if (!Check(S, ", "))",
                         "S", "MCDisassembler::Fail",
                         "  MCDisassembler::DecodeStatus S = "
@@ -148,7 +148,7 @@
     return;
   }
 
-  EmitFixedLenDecoder(Records, OS, std::string(Target.getName()), "if (",
+  EmitDecoder(Records, OS, std::string(Target.getName()), "if (",
                       " == MCDisassembler::Fail)", "MCDisassembler::Success",
                       "MCDisassembler::Fail", "");
 }
diff --git a/llvm/utils/gn/secondary/llvm/utils/TableGen/BUILD.gn b/llvm/utils/gn/secondary/llvm/utils/TableGen/BUILD.gn
--- a/llvm/utils/gn/secondary/llvm/utils/TableGen/BUILD.gn
+++ b/llvm/utils/gn/secondary/llvm/utils/TableGen/BUILD.gn
@@ -27,13 +27,13 @@
     "DAGISelMatcherEmitter.cpp",
     "DAGISelMatcherGen.cpp",
     "DAGISelMatcherOpt.cpp",
+    "DecoderEmitter.cpp",
     "DFAEmitter.cpp",
     "DFAPacketizerEmitter.cpp",
     "DirectiveEmitter.cpp",
     "DisassemblerEmitter.cpp",
     "ExegesisEmitter.cpp",
     "FastISelEmitter.cpp",
-    "FixedLenDecoderEmitter.cpp",
     "GICombinerEmitter.cpp",
     "GlobalISelEmitter.cpp",
     "InfoByHwMode.cpp",