ARM64: Add NEON support

src/arm64/instructions-arm64.h

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_ARM64_INSTRUCTIONS_ARM64_H_
 #define V8_ARM64_INSTRUCTIONS_ARM64_H_
 
 #include "src/arm64/constants-arm64.h"
 #include "src/arm64/utils-arm64.h"
 #include "src/globals.h"
 #include "src/utils.h"
 
 namespace v8 {
 namespace internal {
 
 
 // ISA constants. --------------------------------------------------------------
 
 typedef uint32_t Instr;
 
 // The following macros initialize a float/double variable with a bit pattern
 // without using static initializers: If ARM64_DEFINE_FP_STATICS is defined, the
 // symbol is defined as uint32_t/uint64_t initialized with the desired bit
 // pattern. Otherwise, the same symbol is declared as an external float/double.
 #if defined(ARM64_DEFINE_FP_STATICS)
+#define DEFINE_FLOAT16(name, value) extern const uint16_t name = value
 #define DEFINE_FLOAT(name, value) extern const uint32_t name = value
 #define DEFINE_DOUBLE(name, value) extern const uint64_t name = value
 #else
+#define DEFINE_FLOAT16(name, value) extern const float16 name
 #define DEFINE_FLOAT(name, value) extern const float name
 #define DEFINE_DOUBLE(name, value) extern const double name
 #endif  // defined(ARM64_DEFINE_FP_STATICS)
 
+DEFINE_FLOAT16(kFP16PositiveInfinity, 0x7c00);
+DEFINE_FLOAT16(kFP16NegativeInfinity, 0xfc00);
 DEFINE_FLOAT(kFP32PositiveInfinity, 0x7f800000);
 DEFINE_FLOAT(kFP32NegativeInfinity, 0xff800000);
 DEFINE_DOUBLE(kFP64PositiveInfinity, 0x7ff0000000000000UL);
 DEFINE_DOUBLE(kFP64NegativeInfinity, 0xfff0000000000000UL);
 
 // This value is a signalling NaN as both a double and as a float (taking the
 // least-significant word).
 DEFINE_DOUBLE(kFP64SignallingNaN, 0x7ff000007f800001);
 DEFINE_FLOAT(kFP32SignallingNaN, 0x7f800001);
 
 // A similar value, but as a quiet NaN.
 DEFINE_DOUBLE(kFP64QuietNaN, 0x7ff800007fc00001);
 DEFINE_FLOAT(kFP32QuietNaN, 0x7fc00001);
 
 // The default NaN values (for FPCR.DN=1).
 DEFINE_DOUBLE(kFP64DefaultNaN, 0x7ff8000000000000UL);
 DEFINE_FLOAT(kFP32DefaultNaN, 0x7fc00000);
+DEFINE_FLOAT16(kFP16DefaultNaN, 0x7e00);
 
+#undef DEFINE_FLOAT16
 #undef DEFINE_FLOAT
 #undef DEFINE_DOUBLE
 
-
-enum LSDataSize {
-  LSByte        = 0,
-  LSHalfword    = 1,
-  LSWord        = 2,
-  LSDoubleWord  = 3
-};
-
-LSDataSize CalcLSPairDataSize(LoadStorePairOp op);
+unsigned CalcLSDataSize(LoadStoreOp op);
+unsigned CalcLSPairDataSize(LoadStorePairOp op);
 
 enum ImmBranchType {
   UnknownBranchType = 0,
   CondBranchType    = 1,
   UncondBranchType  = 2,
   CompareBranchType = 3,
   TestBranchType    = 4
 };
 
 enum AddrMode {
   Offset,
   PreIndex,
   PostIndex
 };
 
 enum FPRounding {
   // The first four values are encodable directly by FPCR<RMode>.
   FPTieEven = 0x0,
   FPPositiveInfinity = 0x1,
   FPNegativeInfinity = 0x2,
   FPZero = 0x3,
 
-  // The final rounding mode is only available when explicitly specified by the
-  // instruction (such as with fcvta). It cannot be set in FPCR.
-  FPTieAway
+  // The final rounding modes are only available when explicitly specified by
+  // the instruction (such as with fcvta). They cannot be set in FPCR.
+  FPTieAway,
+  FPRoundOdd
 };
 
 enum Reg31Mode {
   Reg31IsStackPointer,
   Reg31IsZeroRegister
 };
 
 // Instructions. ---------------------------------------------------------------
 
 class Instruction {
@@ skipping 47 matching lines @@
   // ImmPCRel is a compound field (not present in INSTRUCTION_FIELDS_LIST),
   // formed from ImmPCRelLo and ImmPCRelHi.
   int ImmPCRel() const {
     DCHECK(IsPCRelAddressing());
     int offset = ((ImmPCRelHi() << ImmPCRelLo_width) | ImmPCRelLo());
     int width = ImmPCRelLo_width + ImmPCRelHi_width;
     return signed_bitextract_32(width - 1, 0, offset);
   }
 
   uint64_t ImmLogical();
+  unsigned ImmNEONabcdefgh() const;
   float ImmFP32();
   double ImmFP64();
+  float ImmNEONFP32() const;
+  double ImmNEONFP64() const;
 
-  LSDataSize SizeLSPair() const {
+  unsigned SizeLS() const {
+    return CalcLSDataSize(static_cast<LoadStoreOp>(Mask(LoadStoreMask)));
+  }
+
+  unsigned SizeLSPair() const {
     return CalcLSPairDataSize(
         static_cast<LoadStorePairOp>(Mask(LoadStorePairMask)));
   }
 
+  int NEONLSIndex(int access_size_shift) const {
+    int q = NEONQ();
+    int s = NEONS();
+    int size = NEONLSSize();
+    int index = (q << 3) | (s << 2) | size;
+    return index >> access_size_shift;
+  }
+
   // Helpers.
   bool IsCondBranchImm() const {
     return Mask(ConditionalBranchFMask) == ConditionalBranchFixed;
   }
 
   bool IsUncondBranchImm() const {
     return Mask(UnconditionalBranchFMask) == UnconditionalBranchFixed;
   }
 
   bool IsCompareBranch() const {
     return Mask(CompareBranchFMask) == CompareBranchFixed;
   }
 
   bool IsTestBranch() const {
     return Mask(TestBranchFMask) == TestBranchFixed;
   }
 
   bool IsImmBranch() const {
     return BranchType() != UnknownBranchType;
   }
 
+  static float Imm8ToFP32(uint32_t imm8) {
+    //   Imm8: abcdefgh (8 bits)
+    // Single: aBbb.bbbc.defg.h000.0000.0000.0000.0000 (32 bits)
+    // where B is b ^ 1
+    uint32_t bits = imm8;
+    uint32_t bit7 = (bits >> 7) & 0x1;
+    uint32_t bit6 = (bits >> 6) & 0x1;
+    uint32_t bit5_to_0 = bits & 0x3f;
+    uint32_t result = (bit7 << 31) | ((32 - bit6) << 25) | (bit5_to_0 << 19);
+
+    return bit_cast<float>(result);
+  }
+
+  static double Imm8ToFP64(uint32_t imm8) {
+    //   Imm8: abcdefgh (8 bits)
+    // Double: aBbb.bbbb.bbcd.efgh.0000.0000.0000.0000
+    //         0000.0000.0000.0000.0000.0000.0000.0000 (64 bits)
+    // where B is b ^ 1
+    uint32_t bits = imm8;
+    uint64_t bit7 = (bits >> 7) & 0x1;
+    uint64_t bit6 = (bits >> 6) & 0x1;
+    uint64_t bit5_to_0 = bits & 0x3f;
+    uint64_t result = (bit7 << 63) | ((256 - bit6) << 54) | (bit5_to_0 << 48);
+
+    return bit_cast<double>(result);
+  }
+
   bool IsLdrLiteral() const {
     return Mask(LoadLiteralFMask) == LoadLiteralFixed;
   }
 
   bool IsLdrLiteralX() const {
     return Mask(LoadLiteralMask) == LDR_x_lit;
   }
 
   bool IsPCRelAddressing() const {
     return Mask(PCRelAddressingFMask) == PCRelAddressingFixed;
@@ skipping 214 matching lines @@
     return reinterpret_cast<Address>(target) - reinterpret_cast<Address>(this);
   }
 
 
   static const int ImmPCRelRangeBitwidth = 21;
   static bool IsValidPCRelOffset(ptrdiff_t offset) { return is_int21(offset); }
   void SetPCRelImmTarget(Isolate* isolate, Instruction* target);
   void SetBranchImmTarget(Instruction* target);
 };
 
+// Functions for handling NEON vector format information.
+enum VectorFormat {
+  kFormatUndefined = 0xffffffff,
+  kFormat8B = NEON_8B,
+  kFormat16B = NEON_16B,
+  kFormat4H = NEON_4H,
+  kFormat8H = NEON_8H,
+  kFormat2S = NEON_2S,
+  kFormat4S = NEON_4S,
+  kFormat1D = NEON_1D,
+  kFormat2D = NEON_2D,
+
+  // Scalar formats. We add the scalar bit to distinguish between scalar and
+  // vector enumerations; the bit is always set in the encoding of scalar ops
+  // and always clear for vector ops. Although kFormatD and kFormat1D appear
+  // to be the same, their meaning is subtly different. The first is a scalar
+  // operation, the second a vector operation that only affects one lane.
+  kFormatB = NEON_B | NEONScalar,
+  kFormatH = NEON_H | NEONScalar,
+  kFormatS = NEON_S | NEONScalar,
+  kFormatD = NEON_D | NEONScalar
+};
+
+const int kMaxLanesPerVector = 16;

[bbudge, 2017/01/31 01:41:31]

It seems kind of random to have this here. Could this be moved to
constants-arm64.h or logic-arm64.cc?

[martyn.capewell, 2017/02/03 11:01:31]

Done.

+
+VectorFormat VectorFormatHalfWidth(VectorFormat vform);
+VectorFormat VectorFormatDoubleWidth(VectorFormat vform);
+VectorFormat VectorFormatDoubleLanes(VectorFormat vform);
+VectorFormat VectorFormatHalfLanes(VectorFormat vform);
+VectorFormat ScalarFormatFromLaneSize(int lanesize);
+VectorFormat VectorFormatHalfWidthDoubleLanes(VectorFormat vform);
+VectorFormat VectorFormatFillQ(VectorFormat vform);
+VectorFormat ScalarFormatFromFormat(VectorFormat vform);
+unsigned RegisterSizeInBitsFromFormat(VectorFormat vform);
+unsigned RegisterSizeInBytesFromFormat(VectorFormat vform);
+int LaneSizeInBytesFromFormat(VectorFormat vform);
+unsigned LaneSizeInBitsFromFormat(VectorFormat vform);
+int LaneSizeInBytesLog2FromFormat(VectorFormat vform);
+int LaneCountFromFormat(VectorFormat vform);
+int MaxLaneCountFromFormat(VectorFormat vform);
+bool IsVectorFormat(VectorFormat vform);
+int64_t MaxIntFromFormat(VectorFormat vform);
+int64_t MinIntFromFormat(VectorFormat vform);
+uint64_t MaxUintFromFormat(VectorFormat vform);
 
 // Where Instruction looks at instructions generated by the Assembler,
 // InstructionSequence looks at instructions sequences generated by the
 // MacroAssembler.
 class InstructionSequence : public Instruction {
  public:
   static InstructionSequence* At(Address address) {
     return reinterpret_cast<InstructionSequence*>(address);
   }
 
@@ skipping 67 matching lines @@
 // Debug parameters.
 // Used without a TRACE_ option, the Debugger will print the arguments only
 // once. Otherwise TRACE_ENABLE and TRACE_DISABLE will enable or disable tracing
 // before every instruction for the specified LOG_ parameters.
 //
 // TRACE_OVERRIDE enables the specified LOG_ parameters, and disabled any
 // others that were not specified.
 //
 // For example:
 //
-// __ debug("print registers and fp registers", 0, LOG_REGS | LOG_FP_REGS);
+// __ debug("print registers and fp registers", 0, LOG_REGS | LOG_VREGS);
 // will print the registers and fp registers only once.
 //
 // __ debug("trace disasm", 1, TRACE_ENABLE | LOG_DISASM);
 // starts disassembling the code.
 //
 // __ debug("trace rets", 2, TRACE_ENABLE | LOG_REGS);
 // adds the general purpose registers to the trace.
 //
 // __ debug("stop regs", 3, TRACE_DISABLE | LOG_REGS);
 // stops tracing the registers.
 const unsigned kDebuggerTracingDirectivesMask = 3 << 6;
 enum DebugParameters {
-  NO_PARAM       = 0,
-  BREAK          = 1 << 0,
-  LOG_DISASM     = 1 << 1,  // Use only with TRACE. Disassemble the code.
-  LOG_REGS       = 1 << 2,  // Log general purpose registers.
-  LOG_FP_REGS    = 1 << 3,  // Log floating-point registers.
-  LOG_SYS_REGS   = 1 << 4,  // Log the status flags.
-  LOG_WRITE      = 1 << 5,  // Log any memory write.
-
-  LOG_STATE      = LOG_REGS | LOG_FP_REGS | LOG_SYS_REGS,
-  LOG_ALL        = LOG_DISASM | LOG_STATE | LOG_WRITE,
+  NO_PARAM = 0,
+  BREAK = 1 << 0,
+  LOG_DISASM = 1 << 1,    // Use only with TRACE. Disassemble the code.
+  LOG_REGS = 1 << 2,      // Log general purpose registers.
+  LOG_VREGS = 1 << 3,     // Log NEON and floating-point registers.
+  LOG_SYS_REGS = 1 << 4,  // Log the status flags.
+  LOG_WRITE = 1 << 5,     // Log any memory write.
+
+  LOG_NONE = 0,
+  LOG_STATE = LOG_REGS | LOG_VREGS | LOG_SYS_REGS,
+  LOG_ALL = LOG_DISASM | LOG_STATE | LOG_WRITE,
 
   // Trace control.
-  TRACE_ENABLE   = 1 << 6,
-  TRACE_DISABLE  = 2 << 6,
+  TRACE_ENABLE = 1 << 6,
+  TRACE_DISABLE = 2 << 6,
   TRACE_OVERRIDE = 3 << 6
 };
 
+enum NEONFormat {
+  NF_UNDEF = 0,
+  NF_8B = 1,
+  NF_16B = 2,
+  NF_4H = 3,
+  NF_8H = 4,
+  NF_2S = 5,
+  NF_4S = 6,
+  NF_1D = 7,
+  NF_2D = 8,
+  NF_B = 9,
+  NF_H = 10,
+  NF_S = 11,
+  NF_D = 12
+};
+
+static const unsigned kNEONFormatMaxBits = 6;
+
+struct NEONFormatMap {
+  // The bit positions in the instruction to consider.
+  uint8_t bits[kNEONFormatMaxBits];
+
+  // Mapping from concatenated bits to format.
+  NEONFormat map[1 << kNEONFormatMaxBits];
+};
+
+class NEONFormatDecoder {

[bbudge, 2017/01/31 01:41:31]

Is there a reason so much of this class is defined in the header?

[martyn.capewell, 2017/02/03 11:01:31]

I've moved all but the default format maps out of the header.

+ public:
+  enum SubstitutionMode { kPlaceholder, kFormat };
+
+  // Construct a format decoder with increasingly specific format maps for each
+  // subsitution. If no format map is specified, the default is the integer
+  // format map.
+  explicit NEONFormatDecoder(const Instruction* instr) {
+    instrbits_ = instr->InstructionBits();
+    SetFormatMaps(IntegerFormatMap());
+  }
+  NEONFormatDecoder(const Instruction* instr, const NEONFormatMap* format) {
+    instrbits_ = instr->InstructionBits();
+    SetFormatMaps(format);
+  }
+  NEONFormatDecoder(const Instruction* instr, const NEONFormatMap* format0,
+                    const NEONFormatMap* format1) {
+    instrbits_ = instr->InstructionBits();
+    SetFormatMaps(format0, format1);
+  }
+  NEONFormatDecoder(const Instruction* instr, const NEONFormatMap* format0,
+                    const NEONFormatMap* format1,
+                    const NEONFormatMap* format2) {
+    instrbits_ = instr->InstructionBits();
+    SetFormatMaps(format0, format1, format2);
+  }
+
+  // Set the format mapping for all or individual substitutions.
+  void SetFormatMaps(const NEONFormatMap* format0,
+                     const NEONFormatMap* format1 = NULL,
+                     const NEONFormatMap* format2 = NULL) {
+    DCHECK_NOT_NULL(format0);
+    formats_[0] = format0;
+    formats_[1] = (format1 == NULL) ? formats_[0] : format1;
+    formats_[2] = (format2 == NULL) ? formats_[1] : format2;
+  }
+  void SetFormatMap(unsigned index, const NEONFormatMap* format) {
+    DCHECK_LT(index, arraysize(formats_));
+    DCHECK_NOT_NULL(format);
+    formats_[index] = format;
+  }
+
+  // Substitute %s in the input string with the placeholder string for each
+  // register, ie. "'B", "'H", etc.
+  const char* SubstitutePlaceholders(const char* string) {
+    return Substitute(string, kPlaceholder, kPlaceholder, kPlaceholder);
+  }
+
+  // Substitute %s in the input string with a new string based on the
+  // substitution mode.
+  const char* Substitute(const char* string, SubstitutionMode mode0 = kFormat,
+                         SubstitutionMode mode1 = kFormat,
+                         SubstitutionMode mode2 = kFormat) {
+    snprintf(form_buffer_, sizeof(form_buffer_), string,
+             GetSubstitute(0, mode0), GetSubstitute(1, mode1),
+             GetSubstitute(2, mode2));
+    return form_buffer_;
+  }
+
+  // Append a "2" to a mnemonic string based of the state of the Q bit.
+  const char* Mnemonic(const char* mnemonic) {
+    if ((instrbits_ & NEON_Q) != 0) {
+      snprintf(mne_buffer_, sizeof(mne_buffer_), "%s2", mnemonic);
+      return mne_buffer_;
+    }
+    return mnemonic;
+  }
+
+  VectorFormat GetVectorFormat(int format_index = 0) {
+    return GetVectorFormat(formats_[format_index]);
+  }
+
+  VectorFormat GetVectorFormat(const NEONFormatMap* format_map) {
+    static const VectorFormat vform[] = {
+        kFormatUndefined, kFormat8B, kFormat16B, kFormat4H, kFormat8H,
+        kFormat2S,        kFormat4S, kFormat1D,  kFormat2D, kFormatB,
+        kFormatH,         kFormatS,  kFormatD};
+    DCHECK_LT(GetNEONFormat(format_map), arraysize(vform));
+    return vform[GetNEONFormat(format_map)];
+  }
+
+  // Built in mappings for common cases.
+
+  // The integer format map uses three bits (Q, size<1:0>) to encode the
+  // "standard" set of NEON integer vector formats.
+  static const NEONFormatMap* IntegerFormatMap() {
+    static const NEONFormatMap map = {
+        {23, 22, 30},
+        {NF_8B, NF_16B, NF_4H, NF_8H, NF_2S, NF_4S, NF_UNDEF, NF_2D}};
+    return &map;
+  }
+
+  // The long integer format map uses two bits (size<1:0>) to encode the
+  // long set of NEON integer vector formats. These are used in narrow, wide
+  // and long operations.
+  static const NEONFormatMap* LongIntegerFormatMap() {
+    static const NEONFormatMap map = {{23, 22}, {NF_8H, NF_4S, NF_2D}};
+    return &map;
+  }
+
+  // The FP format map uses two bits (Q, size<0>) to encode the NEON FP vector
+  // formats: NF_2S, NF_4S, NF_2D.
+  static const NEONFormatMap* FPFormatMap() {
+    // The FP format map assumes two bits (Q, size<0>) are used to encode the
+    // NEON FP vector formats: NF_2S, NF_4S, NF_2D.
+    static const NEONFormatMap map = {{22, 30},
+                                      {NF_2S, NF_4S, NF_UNDEF, NF_2D}};
+    return &map;
+  }
+
+  // The load/store format map uses three bits (Q, 11, 10) to encode the
+  // set of NEON vector formats.
+  static const NEONFormatMap* LoadStoreFormatMap() {
+    static const NEONFormatMap map = {
+        {11, 10, 30},
+        {NF_8B, NF_16B, NF_4H, NF_8H, NF_2S, NF_4S, NF_1D, NF_2D}};
+    return &map;
+  }
+
+  // The logical format map uses one bit (Q) to encode the NEON vector format:
+  // NF_8B, NF_16B.
+  static const NEONFormatMap* LogicalFormatMap() {
+    static const NEONFormatMap map = {{30}, {NF_8B, NF_16B}};
+    return &map;
+  }
+
+  // The triangular format map uses between two and five bits to encode the NEON
+  // vector format:
+  // xxx10->8B, xxx11->16B, xx100->4H, xx101->8H
+  // x1000->2S, x1001->4S,  10001->2D, all others undefined.
+  static const NEONFormatMap* TriangularFormatMap() {
+    static const NEONFormatMap map = {
+        {19, 18, 17, 16, 30},
+        {NF_UNDEF, NF_UNDEF, NF_8B, NF_16B, NF_4H, NF_8H, NF_8B, NF_16B,
+         NF_2S,    NF_4S,    NF_8B, NF_16B, NF_4H, NF_8H, NF_8B, NF_16B,
+         NF_UNDEF, NF_2D,    NF_8B, NF_16B, NF_4H, NF_8H, NF_8B, NF_16B,
+         NF_2S,    NF_4S,    NF_8B, NF_16B, NF_4H, NF_8H, NF_8B, NF_16B}};
+    return &map;
+  }
+
+  // The scalar format map uses two bits (size<1:0>) to encode the NEON scalar
+  // formats: NF_B, NF_H, NF_S, NF_D.
+  static const NEONFormatMap* ScalarFormatMap() {
+    static const NEONFormatMap map = {{23, 22}, {NF_B, NF_H, NF_S, NF_D}};
+    return &map;
+  }
+
+  // The long scalar format map uses two bits (size<1:0>) to encode the longer
+  // NEON scalar formats: NF_H, NF_S, NF_D.
+  static const NEONFormatMap* LongScalarFormatMap() {
+    static const NEONFormatMap map = {{23, 22}, {NF_H, NF_S, NF_D}};
+    return &map;
+  }
+
+  // The FP scalar format map assumes one bit (size<0>) is used to encode the
+  // NEON FP scalar formats: NF_S, NF_D.
+  static const NEONFormatMap* FPScalarFormatMap() {
+    static const NEONFormatMap map = {{22}, {NF_S, NF_D}};
+    return &map;
+  }
+
+  // The triangular scalar format map uses between one and four bits to encode
+  // the NEON FP scalar formats:
+  // xxx1->B, xx10->H, x100->S, 1000->D, all others undefined.
+  static const NEONFormatMap* TriangularScalarFormatMap() {
+    static const NEONFormatMap map = {
+        {19, 18, 17, 16},
+        {NF_UNDEF, NF_B, NF_H, NF_B, NF_S, NF_B, NF_H, NF_B, NF_D, NF_B, NF_H,
+         NF_B, NF_S, NF_B, NF_H, NF_B}};
+    return &map;
+  }
+
+ private:
+  // Get a pointer to a string that represents the format or placeholder for
+  // the specified substitution index, based on the format map and instruction.
+  const char* GetSubstitute(int index, SubstitutionMode mode) {
+    if (mode == kFormat) {
+      return NEONFormatAsString(GetNEONFormat(formats_[index]));
+    }
+    DCHECK_EQ(mode, kPlaceholder);
+    return NEONFormatAsPlaceholder(GetNEONFormat(formats_[index]));
+  }
+
+  // Get the NEONFormat enumerated value for bits obtained from the
+  // instruction based on the specified format mapping.
+  NEONFormat GetNEONFormat(const NEONFormatMap* format_map) {
+    return format_map->map[PickBits(format_map->bits)];
+  }
+
+  // Convert a NEONFormat into a string.
+  static const char* NEONFormatAsString(NEONFormat format) {
+    static const char* formats[] = {"undefined", "8b", "16b", "4h", "8h",
+                                    "2s",        "4s", "1d",  "2d", "b",
+                                    "h",         "s",  "d"};
+    DCHECK_LT(format, arraysize(formats));
+    return formats[format];
+  }
+
+  // Convert a NEONFormat into a register placeholder string.
+  static const char* NEONFormatAsPlaceholder(NEONFormat format) {
+    DCHECK((format == NF_B) || (format == NF_H) || (format == NF_S) ||
+           (format == NF_D) || (format == NF_UNDEF));
+    static const char* formats[] = {
+        "undefined", "undefined", "undefined", "undefined", "undefined",
+        "undefined", "undefined", "undefined", "undefined", "'B",
+        "'H",        "'S",        "'D"};
+    return formats[format];
+  }
+
+  // Select bits from instrbits_ defined by the bits array, concatenate them,
+  // and return the value.
+  uint8_t PickBits(const uint8_t bits[]) {
+    uint8_t result = 0;
+    for (unsigned b = 0; b < kNEONFormatMaxBits; b++) {
+      if (bits[b] == 0) break;
+      result <<= 1;
+      result |= ((instrbits_ & (1 << bits[b])) == 0) ? 0 : 1;
+    }
+    return result;
+  }
+
+  Instr instrbits_;
+  const NEONFormatMap* formats_[3];
+  char form_buffer_[64];
+  char mne_buffer_[16];
+};
 
 }  // namespace internal
 }  // namespace v8
 
 
 #endif  // V8_ARM64_INSTRUCTIONS_ARM64_H_