Fix memory leaks by avoiding extra manual dynamic allocation
[oota-llvm.git] / utils / TableGen / FixedLenDecoderEmitter.cpp
index 810bd11f60c7803d43480a1c840d4e86e0a54c75..cbf40a90b4d89e9b6850d68e6841ec593e208a12 100644 (file)
@@ -44,9 +44,10 @@ struct EncodingField {
 struct OperandInfo {
   std::vector<EncodingField> Fields;
   std::string Decoder;
+  bool HasCompleteDecoder;
 
-  OperandInfo(std::string D)
-    : Decoder(D) { }
+  OperandInfo(std::string D, bool HCD)
+    : Decoder(D), HasCompleteDecoder(HCD) { }
 
   void addField(unsigned Base, unsigned Width, unsigned Offset) {
     Fields.push_back(EncodingField(Base, Width, Offset));
@@ -85,8 +86,7 @@ public:
   FixedLenDecoderEmitter(RecordKeeper &R,
                          std::string PredicateNamespace,
                          std::string GPrefix  = "if (",
-                         std::string GPostfix = " == MCDisassembler::Fail)"
-                         " return MCDisassembler::Fail;",
+                         std::string GPostfix = " == MCDisassembler::Fail)",
                          std::string ROK      = "MCDisassembler::Success",
                          std::string RFail    = "MCDisassembler::Fail",
                          std::string L        = "") :
@@ -208,7 +208,7 @@ typedef std::vector<bit_value_t> insn_t;
 ///
 /// The Debug output shows the path that the decoding tree follows to reach the
 /// the conclusion that there is a conflict.  VST4q8a is a vst4 to double-spaced
-/// even registers, while VST4q8b is a vst4 to double-spaced odd regsisters.
+/// even registers, while VST4q8b is a vst4 to double-spaced odd registers.
 ///
 /// The encoding info in the .td files does not specify this meta information,
 /// which could have been used by the decoder to resolve the conflict.  The
@@ -333,8 +333,8 @@ protected:
   // Parent emitter
   const FixedLenDecoderEmitter *Emitter;
 
-  FilterChooser(const FilterChooser &) LLVM_DELETED_FUNCTION;
-  void operator=(const FilterChooser &) LLVM_DELETED_FUNCTION;
+  FilterChooser(const FilterChooser &) = delete;
+  void operator=(const FilterChooser &) = delete;
 public:
 
   FilterChooser(const std::vector<const CodeGenInstruction*> &Insts,
@@ -448,10 +448,13 @@ protected:
                                const Filter &Best) const;
 
   void emitBinaryParser(raw_ostream &o, unsigned &Indentation,
-                        const OperandInfo &OpInfo) const;
+                        const OperandInfo &OpInfo,
+                        bool &OpHasCompleteDecoder) const;
 
-  void emitDecoder(raw_ostream &OS, unsigned Indentation, unsigned Opc) const;
-  unsigned getDecoderIndex(DecoderSet &Decoders, unsigned Opc) const;
+  void emitDecoder(raw_ostream &OS, unsigned Indentation, unsigned Opc,
+                   bool &HasCompleteDecoder) const;
+  unsigned getDecoderIndex(DecoderSet &Decoders, unsigned Opc,
+                           bool &HasCompleteDecoder) const;
 
   // Assign a single filter and run with it.
   void runSingleFilter(unsigned startBit, unsigned numBit, bool mixed);
@@ -537,12 +540,10 @@ Filter::~Filter() {
 // instructions.  In order to unambiguously decode the singleton, we need to
 // match the remaining undecoded encoding bits against the singleton.
 void Filter::recurse() {
-  std::map<uint64_t, std::vector<unsigned> >::const_iterator mapIterator;
-
   // Starts by inheriting our parent filter chooser's filter bit values.
   std::vector<bit_value_t> BitValueArray(Owner->FilterBitValues);
 
-  if (VariableInstructions.size()) {
+  if (!VariableInstructions.empty()) {
     // Conservatively marks each segment position as BIT_UNSET.
     for (unsigned bitIndex = 0; bitIndex < NumBits; ++bitIndex)
       BitValueArray[StartBit + bitIndex] = BIT_UNSET;
@@ -564,13 +565,11 @@ void Filter::recurse() {
   }
 
   // Otherwise, create sub choosers.
-  for (mapIterator = FilteredInstructions.begin();
-       mapIterator != FilteredInstructions.end();
-       mapIterator++) {
+  for (const auto &Inst : FilteredInstructions) {
 
     // Marks all the segment positions with either BIT_TRUE or BIT_FALSE.
     for (unsigned bitIndex = 0; bitIndex < NumBits; ++bitIndex) {
-      if (mapIterator->first & (1ULL << bitIndex))
+      if (Inst.first & (1ULL << bitIndex))
         BitValueArray[StartBit + bitIndex] = BIT_TRUE;
       else
         BitValueArray[StartBit + bitIndex] = BIT_FALSE;
@@ -579,8 +578,8 @@ void Filter::recurse() {
     // Delegates to an inferior filter chooser for further processing on this
     // category of instructions.
     FilterChooserMap.insert(std::make_pair(
-        mapIterator->first, llvm::make_unique<FilterChooser>(
-                                Owner->AllInstructions, mapIterator->second,
+        Inst.first, llvm::make_unique<FilterChooser>(
+                                Owner->AllInstructions, Inst.second,
                                 Owner->Operands, BitValueArray, *Owner)));
   }
 }
@@ -614,21 +613,16 @@ void Filter::emitTableEntry(DecoderTableInfo &TableInfo) const {
   TableInfo.Table.push_back(NumBits);
 
   // A new filter entry begins a new scope for fixup resolution.
-  TableInfo.FixupStack.push_back(FixupList());
-
-  std::map<unsigned,
-           std::unique_ptr<const FilterChooser>>::const_iterator filterIterator;
+  TableInfo.FixupStack.emplace_back();
 
   DecoderTable &Table = TableInfo.Table;
 
   size_t PrevFilter = 0;
   bool HasFallthrough = false;
-  for (filterIterator = FilterChooserMap.begin();
-       filterIterator != FilterChooserMap.end();
-       filterIterator++) {
+  for (auto &Filter : FilterChooserMap) {
     // Field value -1 implies a non-empty set of variable instructions.
     // See also recurse().
-    if (filterIterator->first == (unsigned)-1) {
+    if (Filter.first == (unsigned)-1) {
       HasFallthrough = true;
 
       // Each scope should always have at least one filter value to check
@@ -643,7 +637,7 @@ void Filter::emitTableEntry(DecoderTableInfo &TableInfo) const {
       Table.push_back(MCD::OPC_FilterValue);
       // Encode and emit the value to filter against.
       uint8_t Buffer[8];
-      unsigned Len = encodeULEB128(filterIterator->first, Buffer);
+      unsigned Len = encodeULEB128(Filter.first, Buffer);
       Table.insert(Table.end(), Buffer, Buffer + Len);
       // Reserve space for the NumToSkip entry. We'll backpatch the value
       // later.
@@ -656,7 +650,7 @@ void Filter::emitTableEntry(DecoderTableInfo &TableInfo) const {
     // Now delegate to the sub filter chooser for further decodings.
     // The case may fallthrough, which happens if the remaining well-known
     // encoding bits do not match exactly.
-    filterIterator->second->emitTableEntries(TableInfo);
+    Filter.second->emitTableEntries(TableInfo);
 
     // Now that we've emitted the body of the handler, update the NumToSkip
     // of the filter itself to be able to skip forward when false. Subtract
@@ -685,7 +679,7 @@ void Filter::emitTableEntry(DecoderTableInfo &TableInfo) const {
 // Returns the number of fanout produced by the filter.  More fanout implies
 // the filter distinguishes more categories of instructions.
 unsigned Filter::usefulness() const {
-  if (VariableInstructions.size())
+  if (!VariableInstructions.empty())
     return FilteredInstructions.size();
   else
     return FilteredInstructions.size() + 1;
@@ -788,7 +782,9 @@ void FixedLenDecoderEmitter::emitTable(formatted_raw_ostream &OS,
       OS << "// Skip to: " << ((I - Table.begin()) + NumToSkip) << "\n";
       break;
     }
-    case MCD::OPC_Decode: {
+    case MCD::OPC_Decode:
+    case MCD::OPC_TryDecode: {
+      bool IsTry = *I == MCD::OPC_TryDecode;
       ++I;
       // Extract the ULEB128 encoded Opcode to a buffer.
       uint8_t Buffer[8], *p = Buffer;
@@ -797,7 +793,8 @@ void FixedLenDecoderEmitter::emitTable(formatted_raw_ostream &OS,
                && "ULEB128 value too large!");
       // Decode the Opcode value.
       unsigned Opc = decodeULEB128(Buffer);
-      OS.indent(Indentation) << "MCD::OPC_Decode, ";
+      OS.indent(Indentation) << "MCD::OPC_" << (IsTry ? "Try" : "")
+        << "Decode, ";
       for (p = Buffer; *p >= 128; ++p)
         OS << utostr(*p) << ", ";
       OS << utostr(*p) << ", ";
@@ -807,8 +804,25 @@ void FixedLenDecoderEmitter::emitTable(formatted_raw_ostream &OS,
         OS << utostr(*I) << ", ";
       OS << utostr(*I++) << ", ";
 
+      if (!IsTry) {
+        OS << "// Opcode: "
+           << NumberedInstructions->at(Opc)->TheDef->getName() << "\n";
+        break;
+      }
+
+      // Fallthrough for OPC_TryDecode.
+
+      // 16-bit numtoskip value.
+      uint8_t Byte = *I++;
+      uint32_t NumToSkip = Byte;
+      OS << utostr(Byte) << ", ";
+      Byte = *I++;
+      OS << utostr(Byte) << ", ";
+      NumToSkip |= Byte << 8;
+
       OS << "// Opcode: "
-         << NumberedInstructions->at(Opc)->TheDef->getName() << "\n";
+         << NumberedInstructions->at(Opc)->TheDef->getName()
+         << ", skip to: " << ((I - Table.begin()) + NumToSkip) << "\n";
       break;
     }
     case MCD::OPC_SoftFail: {
@@ -857,16 +871,15 @@ emitPredicateFunction(formatted_raw_ostream &OS, PredicateSet &Predicates,
   // The predicate function is just a big switch statement based on the
   // input predicate index.
   OS.indent(Indentation) << "static bool checkDecoderPredicate(unsigned Idx, "
-    << "uint64_t Bits) {\n";
+    << "const FeatureBitset& Bits) {\n";
   Indentation += 2;
   if (!Predicates.empty()) {
     OS.indent(Indentation) << "switch (Idx) {\n";
     OS.indent(Indentation) << "default: llvm_unreachable(\"Invalid index!\");\n";
     unsigned Index = 0;
-    for (PredicateSet::const_iterator I = Predicates.begin(), E = Predicates.end();
-         I != E; ++I, ++Index) {
-      OS.indent(Indentation) << "case " << Index << ":\n";
-      OS.indent(Indentation+2) << "return (" << *I << ");\n";
+    for (const auto &Predicate : Predicates) {
+      OS.indent(Indentation) << "case " << Index++ << ":\n";
+      OS.indent(Indentation+2) << "return (" << Predicate << ");\n";
     }
     OS.indent(Indentation) << "}\n";
   } else {
@@ -886,16 +899,16 @@ emitDecoderFunction(formatted_raw_ostream &OS, DecoderSet &Decoders,
   OS.indent(Indentation) << "static DecodeStatus decodeToMCInst(DecodeStatus S,"
     << " unsigned Idx, InsnType insn, MCInst &MI,\n";
   OS.indent(Indentation) << "                                   uint64_t "
-    << "Address, const void *Decoder) {\n";
+    << "Address, const void *Decoder, bool &DecodeComplete) {\n";
   Indentation += 2;
+  OS.indent(Indentation) << "DecodeComplete = true;\n";
   OS.indent(Indentation) << "InsnType tmp;\n";
   OS.indent(Indentation) << "switch (Idx) {\n";
   OS.indent(Indentation) << "default: llvm_unreachable(\"Invalid index!\");\n";
   unsigned Index = 0;
-  for (DecoderSet::const_iterator I = Decoders.begin(), E = Decoders.end();
-       I != E; ++I, ++Index) {
-    OS.indent(Indentation) << "case " << Index << ":\n";
-    OS << *I;
+  for (const auto &Decoder : Decoders) {
+    OS.indent(Indentation) << "case " << Index++ << ":\n";
+    OS << Decoder;
     OS.indent(Indentation+2) << "return S;\n";
   }
   OS.indent(Indentation) << "}\n";
@@ -1044,65 +1057,69 @@ unsigned FilterChooser::getIslands(std::vector<unsigned> &StartBits,
 }
 
 void FilterChooser::emitBinaryParser(raw_ostream &o, unsigned &Indentation,
-                                     const OperandInfo &OpInfo) const {
+                                     const OperandInfo &OpInfo,
+                                     bool &OpHasCompleteDecoder) const {
   const std::string &Decoder = OpInfo.Decoder;
 
-  if (OpInfo.numFields() == 1) {
-    OperandInfo::const_iterator OI = OpInfo.begin();
-    o.indent(Indentation) << "tmp = fieldFromInstruction"
-                          << "(insn, " << OI->Base << ", " << OI->Width
-                          << ")";
-    if (OI->Offset)
-      o << " << " << OI->Offset;
-    o << ";\n";
-
-  } else {
+  if (OpInfo.numFields() != 1)
     o.indent(Indentation) << "tmp = 0;\n";
-    for (OperandInfo::const_iterator OI = OpInfo.begin(), OE = OpInfo.end();
-         OI != OE; ++OI) {
-      o.indent(Indentation) << "tmp |= (fieldFromInstruction"
-                            << "(insn, " << OI->Base << ", " << OI->Width
-                            << ") << " << OI->Offset << ");\n";
-    }
+
+  for (const EncodingField &EF : OpInfo) {
+    o.indent(Indentation) << "tmp ";
+    if (OpInfo.numFields() != 1) o << '|';
+    o << "= fieldFromInstruction"
+      << "(insn, " << EF.Base << ", " << EF.Width << ')';
+    if (OpInfo.numFields() != 1 || EF.Offset != 0)
+      o << " << " << EF.Offset;
+    o << ";\n";
   }
 
-  if (Decoder != "")
+  if (Decoder != "") {
+    OpHasCompleteDecoder = OpInfo.HasCompleteDecoder;
     o.indent(Indentation) << Emitter->GuardPrefix << Decoder
-                          << "(MI, tmp, Address, Decoder)"
-                          << Emitter->GuardPostfix << "\n";
-  else
-    o.indent(Indentation) << "MI.addOperand(MCOperand::CreateImm(tmp));\n";
-
+      << "(MI, tmp, Address, Decoder)"
+      << Emitter->GuardPostfix
+      << " { " << (OpHasCompleteDecoder ? "" : "DecodeComplete = false; ")
+      << "return MCDisassembler::Fail; }\n";
+  } else {
+    OpHasCompleteDecoder = true;
+    o.indent(Indentation) << "MI.addOperand(MCOperand::createImm(tmp));\n";
+  }
 }
 
 void FilterChooser::emitDecoder(raw_ostream &OS, unsigned Indentation,
-                                unsigned Opc) const {
-  std::map<unsigned, std::vector<OperandInfo> >::const_iterator OpIter =
-    Operands.find(Opc);
-  const std::vector<OperandInfo>& InsnOperands = OpIter->second;
-  for (std::vector<OperandInfo>::const_iterator
-       I = InsnOperands.begin(), E = InsnOperands.end(); I != E; ++I) {
+                                unsigned Opc, bool &HasCompleteDecoder) const {
+  HasCompleteDecoder = true;
+
+  for (const auto &Op : Operands.find(Opc)->second) {
     // If a custom instruction decoder was specified, use that.
-    if (I->numFields() == 0 && I->Decoder.size()) {
-      OS.indent(Indentation) << Emitter->GuardPrefix << I->Decoder
+    if (Op.numFields() == 0 && Op.Decoder.size()) {
+      HasCompleteDecoder = Op.HasCompleteDecoder;
+      OS.indent(Indentation) << Emitter->GuardPrefix << Op.Decoder
         << "(MI, insn, Address, Decoder)"
-        << Emitter->GuardPostfix << "\n";
+        << Emitter->GuardPostfix
+        << " { " << (HasCompleteDecoder ? "" : "DecodeComplete = false; ")
+        << "return MCDisassembler::Fail; }\n";
       break;
     }
 
-    emitBinaryParser(OS, Indentation, *I);
+    bool OpHasCompleteDecoder;
+    emitBinaryParser(OS, Indentation, Op, OpHasCompleteDecoder);
+    if (!OpHasCompleteDecoder)
+      HasCompleteDecoder = false;
   }
 }
 
 unsigned FilterChooser::getDecoderIndex(DecoderSet &Decoders,
-                                        unsigned Opc) const {
+                                        unsigned Opc,
+                                        bool &HasCompleteDecoder) const {
   // Build up the predicate string.
   SmallString<256> Decoder;
   // FIXME: emitDecoder() function can take a buffer directly rather than
   // a stream.
   raw_svector_ostream S(Decoder);
   unsigned I = 4;
-  emitDecoder(S, I, Opc);
+  emitDecoder(S, I, Opc, HasCompleteDecoder);
   S.flush();
 
   // Using the full decoder string as the key value here is a bit
@@ -1112,7 +1129,7 @@ unsigned FilterChooser::getDecoderIndex(DecoderSet &Decoders,
   // overkill for now, though.
 
   // Make sure the predicate is in the table.
-  Decoders.insert(Decoder.str());
+  Decoders.insert(StringRef(Decoder));
   // Now figure out the index for when we write out the table.
   DecoderSet::const_iterator P = std::find(Decoders.begin(),
                                            Decoders.end(),
@@ -1123,17 +1140,18 @@ unsigned FilterChooser::getDecoderIndex(DecoderSet &Decoders,
 static void emitSinglePredicateMatch(raw_ostream &o, StringRef str,
                                      const std::string &PredicateNamespace) {
   if (str[0] == '!')
-    o << "!(Bits & " << PredicateNamespace << "::"
-      << str.slice(1,str.size()) << ")";
+    o << "!Bits[" << PredicateNamespace << "::"
+      << str.slice(1,str.size()) << "]";
   else
-    o << "(Bits & " << PredicateNamespace << "::" << str << ")";
+    o << "Bits[" << PredicateNamespace << "::" << str << "]";
 }
 
 bool FilterChooser::emitPredicateMatch(raw_ostream &o, unsigned &Indentation,
                                        unsigned Opc) const {
   ListInit *Predicates =
     AllInstructions[Opc]->TheDef->getValueAsListInit("Predicates");
-  for (unsigned i = 0; i < Predicates->getSize(); ++i) {
+  bool IsFirstEmission = true;
+  for (unsigned i = 0; i < Predicates->size(); ++i) {
     Record *Pred = Predicates->getElementAsRecord(i);
     if (!Pred->getValue("AssemblerMatcherPredicate"))
       continue;
@@ -1143,7 +1161,7 @@ bool FilterChooser::emitPredicateMatch(raw_ostream &o, unsigned &Indentation,
     if (!P.length())
       continue;
 
-    if (i != 0)
+    if (!IsFirstEmission)
       o << " && ";
 
     StringRef SR(P);
@@ -1154,14 +1172,15 @@ bool FilterChooser::emitPredicateMatch(raw_ostream &o, unsigned &Indentation,
       pairs = pairs.second.split(',');
     }
     emitSinglePredicateMatch(o, pairs.first, Emitter->PredicateNamespace);
+    IsFirstEmission = false;
   }
-  return Predicates->getSize() > 0;
+  return !Predicates->empty();
 }
 
 bool FilterChooser::doesOpcodeNeedPredicate(unsigned Opc) const {
   ListInit *Predicates =
     AllInstructions[Opc]->TheDef->getValueAsListInit("Predicates");
-  for (unsigned i = 0; i < Predicates->getSize(); ++i) {
+  for (unsigned i = 0; i < Predicates->size(); ++i) {
     Record *Pred = Predicates->getElementAsRecord(i);
     if (!Pred->getValue("AssemblerMatcherPredicate"))
       continue;
@@ -1327,14 +1346,26 @@ void FilterChooser::emitSingletonTableEntry(DecoderTableInfo &TableInfo,
   // Check for soft failure of the match.
   emitSoftFailTableEntry(TableInfo, Opc);
 
-  TableInfo.Table.push_back(MCD::OPC_Decode);
+  bool HasCompleteDecoder;
+  unsigned DIdx = getDecoderIndex(TableInfo.Decoders, Opc, HasCompleteDecoder);
+
+  // Produce OPC_Decode or OPC_TryDecode opcode based on the information
+  // whether the instruction decoder is complete or not. If it is complete
+  // then it handles all possible values of remaining variable/unfiltered bits
+  // and for any value can determine if the bitpattern is a valid instruction
+  // or not. This means OPC_Decode will be the final step in the decoding
+  // process. If it is not complete, then the Fail return code from the
+  // decoder method indicates that additional processing should be done to see
+  // if there is any other instruction that also matches the bitpattern and
+  // can decode it.
+  TableInfo.Table.push_back(HasCompleteDecoder ? MCD::OPC_Decode :
+      MCD::OPC_TryDecode);
   uint8_t Buffer[8], *p;
   encodeULEB128(Opc, Buffer);
   for (p = Buffer; *p >= 128 ; ++p)
     TableInfo.Table.push_back(*p);
   TableInfo.Table.push_back(*p);
 
-  unsigned DIdx = getDecoderIndex(TableInfo.Decoders, Opc);
   SmallString<16> Bytes;
   raw_svector_ostream S(Bytes);
   encodeULEB128(DIdx, S);
@@ -1343,6 +1374,14 @@ void FilterChooser::emitSingletonTableEntry(DecoderTableInfo &TableInfo,
   // Decoder index
   for (unsigned i = 0, e = Bytes.size(); i != e; ++i)
     TableInfo.Table.push_back(Bytes[i]);
+
+  if (!HasCompleteDecoder) {
+    // Push location for NumToSkip backpatching.
+    TableInfo.FixupStack.back().push_back(TableInfo.Table.size());
+    // Allocate the space for the fixup.
+    TableInfo.Table.push_back(0);
+    TableInfo.Table.push_back(0);
+  }
 }
 
 // Emits table entries to decode the singleton, and then to decode the rest.
@@ -1352,7 +1391,7 @@ void FilterChooser::emitSingletonTableEntry(DecoderTableInfo &TableInfo,
 
   // complex singletons need predicate checks from the first singleton
   // to refer forward to the variable filterchooser that follows.
-  TableInfo.FixupStack.push_back(FixupList());
+  TableInfo.FixupStack.emplace_back();
 
   emitSingletonTableEntry(TableInfo, Opc);
 
@@ -1369,7 +1408,7 @@ void FilterChooser::emitSingletonTableEntry(DecoderTableInfo &TableInfo,
 void FilterChooser::runSingleFilter(unsigned startBit, unsigned numBit,
                                     bool mixed) {
   Filters.clear();
-  Filters.push_back(Filter(*this, startBit, numBit, true));
+  Filters.emplace_back(*this, startBit, numBit, true);
   BestIndex = 0; // Sole Filter instance to choose from.
   bestFilter().recurse();
 }
@@ -1379,9 +1418,9 @@ void FilterChooser::runSingleFilter(unsigned startBit, unsigned numBit,
 void FilterChooser::reportRegion(bitAttr_t RA, unsigned StartBit,
                                  unsigned BitIndex, bool AllowMixed) {
   if (RA == ATTR_MIXED && AllowMixed)
-    Filters.push_back(Filter(*this, StartBit, BitIndex - StartBit, true));
+    Filters.emplace_back(*this, StartBit, BitIndex - StartBit, true);
   else if (RA == ATTR_ALL_SET && !AllowMixed)
-    Filters.push_back(Filter(*this, StartBit, BitIndex - StartBit, false));
+    Filters.emplace_back(*this, StartBit, BitIndex - StartBit, false);
 }
 
 // FilterProcessor scans the well-known encoding bits of the instructions and
@@ -1698,7 +1737,8 @@ static bool populateInstruction(CodeGenTarget &Target,
   // of trying to auto-generate the decoder.
   std::string InstDecoder = Def.getValueAsString("DecoderMethod");
   if (InstDecoder != "") {
-    InsnOperands.push_back(OperandInfo(InstDecoder));
+    bool HasCompleteInstDecoder = Def.getValueAsBit("hasCompleteDecoder");
+    InsnOperands.push_back(OperandInfo(InstDecoder, HasCompleteInstDecoder));
     Operands[Opc] = InsnOperands;
     return true;
   }
@@ -1801,7 +1841,7 @@ static bool populateInstruction(CodeGenTarget &Target,
       unsigned NumberOps = CGI.Operands.size();
       while (NumberedOp < NumberOps &&
              (CGI.Operands.isFlatOperandNotEmitted(NumberedOp) ||
-              (NamedOpIndices.size() && NamedOpIndices.count(
+              (!NamedOpIndices.empty() && NamedOpIndices.count(
                 CGI.Operands.getSubOperandNumber(NumberedOp).first))))
         ++NumberedOp;
 
@@ -1854,7 +1894,14 @@ static bool populateInstruction(CodeGenTarget &Target,
       if (!isReg && String && String->getValue() != "")
         Decoder = String->getValue();
 
-      OperandInfo OpInfo(Decoder);
+      RecordVal *HasCompleteDecoderVal =
+        TypeRecord->getValue("hasCompleteDecoder");
+      BitInit *HasCompleteDecoderBit = HasCompleteDecoderVal ?
+        dyn_cast<BitInit>(HasCompleteDecoderVal->getValue()) : nullptr;
+      bool HasCompleteDecoder = HasCompleteDecoderBit ?
+        HasCompleteDecoderBit->getValue() : true;
+
+      OperandInfo OpInfo(Decoder, HasCompleteDecoder);
       OpInfo.addField(bitStart, bitWidth, 0);
 
       NumberedInsnOperands[Name].push_back(OpInfo);
@@ -1870,20 +1917,20 @@ static bool populateInstruction(CodeGenTarget &Target,
   }
 
   // For each operand, see if we can figure out where it is encoded.
-  for (std::vector<std::pair<Init*, std::string> >::const_iterator
-       NI = InOutOperands.begin(), NE = InOutOperands.end(); NI != NE; ++NI) {
-    if (!NumberedInsnOperands[NI->second].empty()) {
+  for (const auto &Op : InOutOperands) {
+    if (!NumberedInsnOperands[Op.second].empty()) {
       InsnOperands.insert(InsnOperands.end(),
-                          NumberedInsnOperands[NI->second].begin(),
-                          NumberedInsnOperands[NI->second].end());
+                          NumberedInsnOperands[Op.second].begin(),
+                          NumberedInsnOperands[Op.second].end());
       continue;
-    } else if (!NumberedInsnOperands[TiedNames[NI->second]].empty()) {
-      if (!NumberedInsnOperandsNoTie.count(TiedNames[NI->second])) {
+    }
+    if (!NumberedInsnOperands[TiedNames[Op.second]].empty()) {
+      if (!NumberedInsnOperandsNoTie.count(TiedNames[Op.second])) {
         // Figure out to which (sub)operand we're tied.
-        unsigned i = CGI.Operands.getOperandNamed(TiedNames[NI->second]);
+        unsigned i = CGI.Operands.getOperandNamed(TiedNames[Op.second]);
         int tiedTo = CGI.Operands[i].getTiedRegister();
         if (tiedTo == -1) {
-          i = CGI.Operands.getOperandNamed(NI->second);
+          i = CGI.Operands.getOperandNamed(Op.second);
           tiedTo = CGI.Operands[i].getTiedRegister();
         }
 
@@ -1891,7 +1938,7 @@ static bool populateInstruction(CodeGenTarget &Target,
           std::pair<unsigned, unsigned> SO =
             CGI.Operands.getSubOperandNumber(tiedTo);
 
-          InsnOperands.push_back(NumberedInsnOperands[TiedNames[NI->second]]
+          InsnOperands.push_back(NumberedInsnOperands[TiedNames[Op.second]]
                                    [SO.second]);
         }
       }
@@ -1905,7 +1952,7 @@ static bool populateInstruction(CodeGenTarget &Target,
     // for decoding register classes.
     // FIXME: This need to be extended to handle instructions with custom
     // decoder methods, and operands with (simple) MIOperandInfo's.
-    TypedInit *TI = cast<TypedInit>(NI->first);
+    TypedInit *TI = cast<TypedInit>(Op.first);
     RecordRecTy *Type = cast<RecordRecTy>(TI->getType());
     Record *TypeRecord = Type->getRecord();
     bool isReg = false;
@@ -1926,7 +1973,14 @@ static bool populateInstruction(CodeGenTarget &Target,
     if (!isReg && String && String->getValue() != "")
       Decoder = String->getValue();
 
-    OperandInfo OpInfo(Decoder);
+    RecordVal *HasCompleteDecoderVal =
+      TypeRecord->getValue("hasCompleteDecoder");
+    BitInit *HasCompleteDecoderBit = HasCompleteDecoderVal ?
+      dyn_cast<BitInit>(HasCompleteDecoderVal->getValue()) : nullptr;
+    bool HasCompleteDecoder = HasCompleteDecoderBit ?
+      HasCompleteDecoderBit->getValue() : true;
+
+    OperandInfo OpInfo(Decoder, HasCompleteDecoder);
     unsigned Base = ~0U;
     unsigned Width = 0;
     unsigned Offset = 0;
@@ -1949,8 +2003,8 @@ static bool populateInstruction(CodeGenTarget &Target,
         continue;
       }
 
-      if (Var->getName() != NI->second &&
-          Var->getName() != TiedNames[NI->second]) {
+      if (Var->getName() != Op.second &&
+          Var->getName() != TiedNames[Op.second]) {
         if (Base != ~0U) {
           OpInfo.addField(Base, Width, Offset);
           Base = ~0U;
@@ -2031,7 +2085,7 @@ static void emitDecodeInstruction(formatted_raw_ostream &OS) {
      << "                                      InsnType insn, uint64_t Address,\n"
      << "                                      const void *DisAsm,\n"
      << "                                      const MCSubtargetInfo &STI) {\n"
-     << "  uint64_t Bits = STI.getFeatureBits();\n"
+     << "  const FeatureBitset& Bits = STI.getFeatureBits();\n"
      << "\n"
      << "  const uint8_t *Ptr = DecodeTable;\n"
      << "  uint32_t CurFieldValue = 0;\n"
@@ -2115,12 +2169,51 @@ static void emitDecodeInstruction(formatted_raw_ostream &OS) {
      << "      Ptr += Len;\n"
      << "      unsigned DecodeIdx = decodeULEB128(Ptr, &Len);\n"
      << "      Ptr += Len;\n"
-     << "      DEBUG(dbgs() << Loc << \": OPC_Decode: opcode \" << Opc\n"
-     << "                   << \", using decoder \" << DecodeIdx << \"\\n\" );\n"
-     << "      DEBUG(dbgs() << \"----- DECODE SUCCESSFUL -----\\n\");\n"
      << "\n"
      << "      MI.setOpcode(Opc);\n"
-     << "      return decodeToMCInst(S, DecodeIdx, insn, MI, Address, DisAsm);\n"
+     << "      bool DecodeComplete;\n"
+     << "      S = decodeToMCInst(S, DecodeIdx, insn, MI, Address, DisAsm, DecodeComplete);\n"
+     << "      assert(DecodeComplete);\n"
+     << "\n"
+     << "      DEBUG(dbgs() << Loc << \": OPC_Decode: opcode \" << Opc\n"
+     << "                   << \", using decoder \" << DecodeIdx << \": \"\n"
+     << "                   << (S != MCDisassembler::Fail ? \"PASS\" : \"FAIL\") << \"\\n\");\n"
+     << "      return S;\n"
+     << "    }\n"
+     << "    case MCD::OPC_TryDecode: {\n"
+     << "      unsigned Len;\n"
+     << "      // Decode the Opcode value.\n"
+     << "      unsigned Opc = decodeULEB128(++Ptr, &Len);\n"
+     << "      Ptr += Len;\n"
+     << "      unsigned DecodeIdx = decodeULEB128(Ptr, &Len);\n"
+     << "      Ptr += Len;\n"
+     << "      // NumToSkip is a plain 16-bit integer.\n"
+     << "      unsigned NumToSkip = *Ptr++;\n"
+     << "      NumToSkip |= (*Ptr++) << 8;\n"
+     << "\n"
+     << "      // Perform the decode operation.\n"
+     << "      MCInst TmpMI;\n"
+     << "      TmpMI.setOpcode(Opc);\n"
+     << "      bool DecodeComplete;\n"
+     << "      S = decodeToMCInst(S, DecodeIdx, insn, TmpMI, Address, DisAsm, DecodeComplete);\n"
+     << "      DEBUG(dbgs() << Loc << \": OPC_TryDecode: opcode \" << Opc\n"
+     << "                   << \", using decoder \" << DecodeIdx << \": \");\n"
+     << "\n"
+     << "      if (DecodeComplete) {\n"
+     << "        // Decoding complete.\n"
+     << "        DEBUG(dbgs() << (S != MCDisassembler::Fail ? \"PASS\" : \"FAIL\") << \"\\n\");\n"
+     << "        MI = TmpMI;\n"
+     << "        return S;\n"
+     << "      } else {\n"
+     << "        assert(S == MCDisassembler::Fail);\n"
+     << "        // If the decoding was incomplete, skip.\n"
+     << "        Ptr += NumToSkip;\n"
+     << "        DEBUG(dbgs() << \"FAIL: continuing at \" << (Ptr - DecodeTable) << \"\\n\");\n"
+     << "        // Reset decode status. This also drops a SoftFail status that could be\n"
+     << "        // set before the decode attempt.\n"
+     << "        S = MCDisassembler::Success;\n"
+     << "      }\n"
+     << "      break;\n"
      << "    }\n"
      << "    case MCD::OPC_SoftFail: {\n"
      << "      // Decode the mask values.\n"
@@ -2187,12 +2280,10 @@ void FixedLenDecoderEmitter::run(raw_ostream &o) {
   }
 
   DecoderTableInfo TableInfo;
-  for (std::map<std::pair<std::string, unsigned>,
-                std::vector<unsigned> >::const_iterator
-       I = OpcMap.begin(), E = OpcMap.end(); I != E; ++I) {
+  for (const auto &Opc : OpcMap) {
     // Emit the decoder for this namespace+width combination.
-    FilterChooser FC(*NumberedInstructions, I->second, Operands,
-                     8*I->first.second, this);
+    FilterChooser FC(*NumberedInstructions, Opc.second, Operands,
+                     8*Opc.first.second, this);
 
     // The decode table is cleared for each top level decoder function. The
     // predicates and decoders themselves, however, are shared across all
@@ -2200,7 +2291,7 @@ void FixedLenDecoderEmitter::run(raw_ostream &o) {
     TableInfo.Table.clear();
     TableInfo.FixupStack.clear();
     TableInfo.Table.reserve(16384);
-    TableInfo.FixupStack.push_back(FixupList());
+    TableInfo.FixupStack.emplace_back();
     FC.emitTableEntries(TableInfo);
     // Any NumToSkip fixups in the top level scope can resolve to the
     // OPC_Fail at the end of the table.
@@ -2213,7 +2304,7 @@ void FixedLenDecoderEmitter::run(raw_ostream &o) {
     TableInfo.Table.push_back(MCD::OPC_Fail);
 
     // Print the table to the output stream.
-    emitTable(OS, TableInfo.Table, 0, FC.getBitWidth(), I->first.first);
+    emitTable(OS, TableInfo.Table, 0, FC.getBitWidth(), Opc.first.first);
     OS.flush();
   }