Index: lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
===================================================================
--- lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
+++ lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
@@ -1972,7 +1972,8 @@
 
     bool Valid;
     auto Mapper = AArch64PRFM::PRFMMapper();
-    StringRef Name = Mapper.toString(MCE->getValue(), Valid);
+    StringRef Name = 
+        Mapper.toString(MCE->getValue(), STI.getFeatureBits(), Valid);
     Operands.push_back(AArch64Operand::CreatePrefetch(prfop, Name,
                                                       S, getContext()));
     return MatchOperand_Success;
@@ -1985,7 +1986,8 @@
 
   bool Valid;
   auto Mapper = AArch64PRFM::PRFMMapper();
-  unsigned prfop = Mapper.fromString(Tok.getString(), Valid);
+  unsigned prfop = 
+      Mapper.fromString(Tok.getString(), STI.getFeatureBits(), Valid);
   if (!Valid) {
     TokError("pre-fetch hint expected");
     return MatchOperand_ParseFail;
@@ -2597,7 +2599,8 @@
     }
     bool Valid;
     auto Mapper = AArch64DB::DBarrierMapper();
-    StringRef Name = Mapper.toString(MCE->getValue(), Valid);
+    StringRef Name = 
+        Mapper.toString(MCE->getValue(), STI.getFeatureBits(), Valid);
     Operands.push_back( AArch64Operand::CreateBarrier(MCE->getValue(), Name,
                                                       ExprLoc, getContext()));
     return MatchOperand_Success;
@@ -2610,7 +2613,8 @@
 
   bool Valid;
   auto Mapper = AArch64DB::DBarrierMapper();
-  unsigned Opt = Mapper.fromString(Tok.getString(), Valid);
+  unsigned Opt = 
+      Mapper.fromString(Tok.getString(), STI.getFeatureBits(), Valid);
   if (!Valid) {
     TokError("invalid barrier option name");
     return MatchOperand_ParseFail;
@@ -2651,7 +2655,8 @@
          "register should be -1 if and only if it's unknown");
 
   auto PStateMapper = AArch64PState::PStateMapper();
-  uint32_t PStateField = PStateMapper.fromString(Tok.getString(), IsKnown);
+  uint32_t PStateField = 
+      PStateMapper.fromString(Tok.getString(), STI.getFeatureBits(), IsKnown);
   assert(IsKnown == (PStateField != -1U) &&
          "register should be -1 if and only if it's unknown");
 
Index: lib/Target/AArch64/Disassembler/AArch64Disassembler.cpp
===================================================================
--- lib/Target/AArch64/Disassembler/AArch64Disassembler.cpp
+++ lib/Target/AArch64/Disassembler/AArch64Disassembler.cpp
@@ -1504,7 +1504,10 @@
   Inst.addOperand(MCOperand::CreateImm(crm));
 
   bool ValidNamed;
-  (void)AArch64PState::PStateMapper().toString(pstate_field, ValidNamed);
+  const AArch64Disassembler *Dis = 
+      static_cast<const AArch64Disassembler *>(Decoder);
+  (void)AArch64PState::PStateMapper().toString(pstate_field, 
+      Dis->getSubtargetInfo().getFeatureBits(), ValidNamed);
 
   return ValidNamed ? Success : Fail;
 }
Index: lib/Target/AArch64/InstPrinter/AArch64InstPrinter.cpp
===================================================================
--- lib/Target/AArch64/InstPrinter/AArch64InstPrinter.cpp
+++ lib/Target/AArch64/InstPrinter/AArch64InstPrinter.cpp
@@ -1088,7 +1088,8 @@
                                          raw_ostream &O) {
   unsigned prfop = MI->getOperand(OpNum).getImm();
   bool Valid;
-  StringRef Name = AArch64PRFM::PRFMMapper().toString(prfop, Valid);
+  StringRef Name = 
+      AArch64PRFM::PRFMMapper().toString(prfop, getAvailableFeatures(), Valid);
   if (Valid)
     O << Name;
   else
@@ -1263,9 +1264,11 @@
   bool Valid;
   StringRef Name;
   if (Opcode == AArch64::ISB)
-    Name = AArch64ISB::ISBMapper().toString(Val, Valid);
+    Name = AArch64ISB::ISBMapper().toString(Val, getAvailableFeatures(), 
+                                            Valid);
   else
-    Name = AArch64DB::DBarrierMapper().toString(Val, Valid);
+    Name = AArch64DB::DBarrierMapper().toString(Val, getAvailableFeatures(), 
+                                                Valid);
   if (Valid)
     O << Name;
   else
@@ -1297,7 +1300,8 @@
   unsigned Val = MI->getOperand(OpNo).getImm();
 
   bool Valid;
-  StringRef Name = AArch64PState::PStateMapper().toString(Val, Valid);
+  StringRef Name = 
+      AArch64PState::PStateMapper().toString(Val, getAvailableFeatures(), Valid);
   if (Valid)
     O << StringRef(Name.str()).upper();
   else
Index: lib/Target/AArch64/Utils/AArch64BaseInfo.h
===================================================================
--- lib/Target/AArch64/Utils/AArch64BaseInfo.h
+++ lib/Target/AArch64/Utils/AArch64BaseInfo.h
@@ -280,14 +280,22 @@
   struct Mapping {
     const char *Name;
     uint32_t Value;
+    uint64_t AvailableForFeatures;
+    // empty AvailableForFeatures means "always-on"
+    template <typename T> bool isEqual(T Other) const;
+    template <typename T> bool isEqual(T Other, uint64_t FeatureBits) const {
+      if (AvailableForFeatures && !(AvailableForFeatures & FeatureBits))
+        return false;
+      return isEqual<T>(Other);
+    }
   };
 
   template<int N>
   AArch64NamedImmMapper(const Mapping (&Mappings)[N], uint32_t TooBigImm)
     : Mappings(&Mappings[0]), NumMappings(N), TooBigImm(TooBigImm) {}
 
-  StringRef toString(uint32_t Value, bool &Valid) const;
-  uint32_t fromString(StringRef Name, bool &Valid) const;
+  StringRef toString(uint32_t Value, uint64_t FeatureBits, bool &Valid) const;
+  uint32_t fromString(StringRef Name, uint64_t FeatureBits, bool &Valid) const;
 
   /// Many of the instructions allow an alternative assembly form consisting of
   /// a simple immediate. Currently the only valid forms are ranges [0, N) where
@@ -299,6 +307,15 @@
   uint32_t TooBigImm;
 };
 
+template <>
+inline bool AArch64NamedImmMapper::Mapping::isEqual(std::string Other) const {
+  return Name == Other; 
+}
+template <>
+inline bool AArch64NamedImmMapper::Mapping::isEqual(uint32_t Other) const {
+  return Value == Other; 
+}
+
 namespace AArch64AT {
   enum ATValues {
     Invalid = -1,    // Op0 Op1  CRn   CRm   Op2
Index: lib/Target/AArch64/Utils/AArch64BaseInfo.cpp
===================================================================
--- lib/Target/AArch64/Utils/AArch64BaseInfo.cpp
+++ lib/Target/AArch64/Utils/AArch64BaseInfo.cpp
@@ -18,9 +18,10 @@
 
 using namespace llvm;
 
-StringRef AArch64NamedImmMapper::toString(uint32_t Value, bool &Valid) const {
+StringRef AArch64NamedImmMapper::toString(uint32_t Value, uint64_t FeatureBits,
+                                          bool &Valid) const {
   for (unsigned i = 0; i < NumMappings; ++i) {
-    if (Mappings[i].Value == Value) {
+    if (Mappings[i].isEqual(Value, FeatureBits)) {
       Valid = true;
       return Mappings[i].Name;
     }
@@ -30,10 +31,11 @@
   return StringRef();
 }
 
-uint32_t AArch64NamedImmMapper::fromString(StringRef Name, bool &Valid) const {
+uint32_t AArch64NamedImmMapper::fromString(StringRef Name, uint64_t FeatureBits,
+                                           bool &Valid) const {
   std::string LowerCaseName = Name.lower();
   for (unsigned i = 0; i < NumMappings; ++i) {
-    if (Mappings[i].Name == LowerCaseName) {
+    if (Mappings[i].isEqual(LowerCaseName, FeatureBits)) {
       Valid = true;
       return Mappings[i].Value;
     }
@@ -765,7 +767,7 @@
 
   // First search the registers shared by all
   for (unsigned i = 0; i < array_lengthof(SysRegMappings); ++i) {
-    if (SysRegMappings[i].Name == NameLower) {
+    if (SysRegMappings[i].isEqual(NameLower, FeatureBits)) {
       Valid = true;
       return SysRegMappings[i].Value;
     }
@@ -784,7 +786,7 @@
   // Now try the instruction-specific registers (either read-only or
   // write-only).
   for (unsigned i = 0; i < NumInstMappings; ++i) {
-    if (InstMappings[i].Name == NameLower) {
+    if (InstMappings[i].isEqual(NameLower, FeatureBits)) {
       Valid = true;
       return InstMappings[i].Value;
     }
@@ -816,7 +818,7 @@
 AArch64SysReg::SysRegMapper::toString(uint32_t Bits, uint64_t FeatureBits) const {
   // First search the registers shared by all
   for (unsigned i = 0; i < array_lengthof(SysRegMappings); ++i) {
-    if (SysRegMappings[i].Value == Bits) {
+    if (SysRegMappings[i].isEqual(Bits, FeatureBits)) {
       return SysRegMappings[i].Name;
     }
   }
@@ -833,7 +835,7 @@
   // Now try the instruction-specific registers (either read-only or
   // write-only).
   for (unsigned i = 0; i < NumInstMappings; ++i) {
-    if (InstMappings[i].Value == Bits) {
+    if (InstMappings[i].isEqual(Bits, FeatureBits)) {
       return InstMappings[i].Name;
     }
   }