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llvm-project/llvm/utils/TableGen/DecoderEmitter.cpp

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//===---------------- 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.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// It contains the tablegen backend that emits the decoder functions for
// targets with fixed/variable length instruction set.
//
//===----------------------------------------------------------------------===//
#include "Common/CodeGenHwModes.h"
#include "Common/CodeGenInstruction.h"
#include "Common/CodeGenTarget.h"
#include "Common/InfoByHwMode.h"
#include "Common/VarLenCodeEmitterGen.h"
#include "TableGenBackends.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/CachedHashString.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallBitVector.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/MC/MCDecoderOps.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/FormatVariadic.h"
#include "llvm/Support/FormattedStream.h"
#include "llvm/Support/KnownBits.h"
#include "llvm/Support/LEB128.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/TableGen/Error.h"
#include "llvm/TableGen/Record.h"
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <map>
#include <memory>
#include <set>
#include <string>
#include <utility>
#include <vector>
using namespace llvm;
#define DEBUG_TYPE "decoder-emitter"
extern cl::OptionCategory DisassemblerEmitterCat;
enum SuppressLevel {
SUPPRESSION_DISABLE,
SUPPRESSION_LEVEL1,
SUPPRESSION_LEVEL2
};
static cl::opt<SuppressLevel> DecoderEmitterSuppressDuplicates(
"suppress-per-hwmode-duplicates",
cl::desc("Suppress duplication of instrs into per-HwMode decoder tables"),
cl::values(
clEnumValN(
SUPPRESSION_DISABLE, "O0",
"Do not prevent DecoderTable duplications caused by HwModes"),
clEnumValN(
SUPPRESSION_LEVEL1, "O1",
"Remove duplicate DecoderTable entries generated due to HwModes"),
clEnumValN(
SUPPRESSION_LEVEL2, "O2",
"Extract HwModes-specific instructions into new DecoderTables, "
"significantly reducing Table Duplications")),
cl::init(SUPPRESSION_DISABLE), cl::cat(DisassemblerEmitterCat));
static cl::opt<bool> LargeTable(
"large-decoder-table",
cl::desc("Use large decoder table format. This uses 24 bits for offset\n"
"in the table instead of the default 16 bits."),
cl::init(false), cl::cat(DisassemblerEmitterCat));
static cl::opt<bool> UseFnTableInDecodeToMCInst(
"use-fn-table-in-decode-to-mcinst",
cl::desc(
"Use a table of function pointers instead of a switch case in the\n"
"generated `decodeToMCInst` function. Helps improve compile time\n"
"of the generated code."),
cl::init(false), cl::cat(DisassemblerEmitterCat));
// Enabling this option requires use of different `InsnType` for different
// bitwidths and defining `InsnBitWidth` template specialization for the
// `InsnType` types used. Some common specializations are already defined in
// MCDecoder.h.
static cl::opt<bool> SpecializeDecodersPerBitwidth(
"specialize-decoders-per-bitwidth",
cl::desc("Specialize the generated `decodeToMCInst` function per bitwidth. "
"Helps reduce the code size."),
cl::init(false), cl::cat(DisassemblerEmitterCat));
static cl::opt<bool> IgnoreNonDecodableOperands(
"ignore-non-decodable-operands",
cl::desc(
"Do not issue an error if an operand cannot be decoded automatically."),
cl::init(false), cl::cat(DisassemblerEmitterCat));
static cl::opt<bool> IgnoreFullyDefinedOperands(
"ignore-fully-defined-operands",
cl::desc(
"Do not automatically decode operands with no '?' in their encoding."),
cl::init(false), cl::cat(DisassemblerEmitterCat));
STATISTIC(NumEncodings, "Number of encodings considered");
STATISTIC(NumEncodingsLackingDisasm,
"Number of encodings without disassembler info");
STATISTIC(NumInstructions, "Number of instructions considered");
STATISTIC(NumEncodingsSupported, "Number of encodings supported");
STATISTIC(NumEncodingsOmitted, "Number of encodings omitted");
static unsigned getNumToSkipInBytes() { return LargeTable ? 3 : 2; }
/// Similar to KnownBits::print(), but allows you to specify a character to use
/// to print unknown bits.
static void printKnownBits(raw_ostream &OS, const KnownBits &Bits,
char Unknown) {
for (unsigned I = Bits.getBitWidth(); I--;) {
if (Bits.Zero[I] && Bits.One[I])
OS << '!';
else if (Bits.Zero[I])
OS << '0';
else if (Bits.One[I])
OS << '1';
else
OS << Unknown;
}
}
namespace {
// Represents a span of bits in the instruction encoding that's based on a span
// of bits in an operand's encoding.
//
// Width is the width of the span.
// Base is the starting position of that span in the instruction encoding.
// Offset if the starting position of that span in the operand's encoding.
// That is, bits {Base + Width - 1, Base} in the instruction encoding form
// bits {Offset + Width - 1, Offset} in the operands encoding.
struct EncodingField {
unsigned Base, Width, Offset;
EncodingField(unsigned B, unsigned W, unsigned O)
: Base(B), Width(W), Offset(O) {}
};
struct OperandInfo {
std::vector<EncodingField> Fields;
std::string Decoder;
bool HasCompleteDecoder;
std::optional<uint64_t> InitValue;
OperandInfo(std::string D, bool HCD) : Decoder(D), HasCompleteDecoder(HCD) {}
void addField(unsigned Base, unsigned Width, unsigned Offset) {
Fields.emplace_back(Base, Width, Offset);
}
unsigned numFields() const { return Fields.size(); }
ArrayRef<EncodingField> fields() const { return Fields; }
};
/// Represents a parsed InstructionEncoding record or a record derived from it.
class InstructionEncoding {
/// The Record this encoding originates from.
const Record *EncodingDef;
/// The instruction this encoding is for.
const CodeGenInstruction *Inst;
/// The name of this encoding (for debugging purposes).
std::string Name;
/// The namespace in which this encoding exists.
StringRef DecoderNamespace;
/// Known bits of this encoding. This is the value of the `Inst` field
/// with any variable references replaced with '?'.
KnownBits InstBits;
/// Mask of bits that should be considered unknown during decoding.
/// This is the value of the `SoftFail` field.
APInt SoftFailMask;
/// The name of the function to use for decoding. May be an empty string,
/// meaning the decoder is generated.
StringRef DecoderMethod;
/// Whether the custom decoding function always succeeds. If a custom decoder
/// function is specified, the value is taken from the target description,
/// otherwise it is inferred.
bool HasCompleteDecoder;
/// Information about the operands' contribution to this encoding.
SmallVector<OperandInfo, 16> Operands;
public:
InstructionEncoding(const Record *EncodingDef,
const CodeGenInstruction *Inst);
/// Returns the Record this encoding originates from.
const Record *getRecord() const { return EncodingDef; }
/// Returns the instruction this encoding is for.
const CodeGenInstruction *getInstruction() const { return Inst; }
/// Returns the name of this encoding, for debugging purposes.
StringRef getName() const { return Name; }
/// Returns the namespace in which this encoding exists.
StringRef getDecoderNamespace() const { return DecoderNamespace; }
/// Returns the size of this encoding, in bits.
unsigned getBitWidth() const { return InstBits.getBitWidth(); }
/// Returns the known bits of this encoding.
const KnownBits &getInstBits() const { return InstBits; }
/// Returns a mask of bits that should be considered unknown during decoding.
const APInt &getSoftFailMask() const { return SoftFailMask; }
/// Returns the known bits of this encoding that must match for
/// successful decoding.
KnownBits getMandatoryBits() const {
KnownBits EncodingBits = InstBits;
// Mark all bits that are allowed to change according to SoftFail mask
// as unknown.
EncodingBits.Zero &= ~SoftFailMask;
EncodingBits.One &= ~SoftFailMask;
return EncodingBits;
}
/// Returns the name of the function to use for decoding, or an empty string
/// if the decoder is generated.
StringRef getDecoderMethod() const { return DecoderMethod; }
/// Returns whether the decoder (either generated or specified by the user)
/// always succeeds.
bool hasCompleteDecoder() const { return HasCompleteDecoder; }
/// Returns information about the operands' contribution to this encoding.
ArrayRef<OperandInfo> getOperands() const { return Operands; }
private:
void parseVarLenEncoding(const VarLenInst &VLI);
void parseFixedLenEncoding(const BitsInit &RecordInstBits);
void parseVarLenOperands(const VarLenInst &VLI);
void parseFixedLenOperands(const BitsInit &Bits);
};
/// Sorting predicate to sort encoding IDs by encoding width.
class LessEncodingIDByWidth {
ArrayRef<InstructionEncoding> Encodings;
public:
explicit LessEncodingIDByWidth(ArrayRef<InstructionEncoding> Encodings)
: Encodings(Encodings) {}
bool operator()(unsigned ID1, unsigned ID2) const {
return Encodings[ID1].getBitWidth() < Encodings[ID2].getBitWidth();
}
};
typedef SmallSetVector<CachedHashString, 16> PredicateSet;
typedef SmallSetVector<CachedHashString, 16> DecoderSet;
class DecoderTable {
public:
DecoderTable() { Data.reserve(16384); }
void clear() { Data.clear(); }
size_t size() const { return Data.size(); }
const uint8_t *data() const { return Data.data(); }
using const_iterator = std::vector<uint8_t>::const_iterator;
const_iterator begin() const { return Data.begin(); }
const_iterator end() const { return Data.end(); }
/// Inserts a state machine opcode into the table.
void insertOpcode(MCD::DecoderOps Opcode) { Data.push_back(Opcode); }
/// Inserts a uint8 encoded value into the table.
void insertUInt8(unsigned Value) {
assert(isUInt<8>(Value));
Data.push_back(Value);
}
/// Inserts a ULEB128 encoded value into the table.
void insertULEB128(uint64_t Value) {
// Encode and emit the value to filter against.
uint8_t Buffer[16];
unsigned Len = encodeULEB128(Value, Buffer);
Data.insert(Data.end(), Buffer, Buffer + Len);
}
// Insert space for `NumToSkip` and return the position
// in the table for patching.
size_t insertNumToSkip() {
size_t Size = Data.size();
Data.insert(Data.end(), getNumToSkipInBytes(), 0);
return Size;
}
void patchNumToSkip(size_t FixupIdx, uint32_t DestIdx) {
// Calculate the distance from the byte following the fixup entry byte
// to the destination. The Target is calculated from after the
// `getNumToSkipInBytes()`-byte NumToSkip entry itself, so subtract
// `getNumToSkipInBytes()` from the displacement here to account for that.
assert(DestIdx >= FixupIdx + getNumToSkipInBytes() &&
"Expecting a forward jump in the decoding table");
uint32_t Delta = DestIdx - FixupIdx - getNumToSkipInBytes();
if (!isUIntN(8 * getNumToSkipInBytes(), Delta))
PrintFatalError(
"disassembler decoding table too large, try --large-decoder-table");
Data[FixupIdx] = static_cast<uint8_t>(Delta);
Data[FixupIdx + 1] = static_cast<uint8_t>(Delta >> 8);
if (getNumToSkipInBytes() == 3)
Data[FixupIdx + 2] = static_cast<uint8_t>(Delta >> 16);
}
private:
std::vector<uint8_t> Data;
};
struct DecoderTableInfo {
DecoderTable Table;
PredicateSet Predicates;
DecoderSet Decoders;
};
using NamespacesHwModesMap = std::map<StringRef, std::set<unsigned>>;
class DecoderEmitter {
const RecordKeeper &RK;
CodeGenTarget Target;
const CodeGenHwModes &CGH;
/// All parsed encodings.
std::vector<InstructionEncoding> Encodings;
/// Encodings IDs for each HwMode. An ID is an index into Encodings.
SmallDenseMap<unsigned, std::vector<unsigned>> EncodingIDsByHwMode;
public:
explicit DecoderEmitter(const RecordKeeper &RK);
const CodeGenTarget &getTarget() const { return Target; }
// Emit the decoder state machine table. Returns a mask of MCD decoder ops
// that were emitted.
unsigned emitTable(formatted_raw_ostream &OS, DecoderTable &Table,
StringRef Namespace, unsigned HwModeID, unsigned BitWidth,
ArrayRef<unsigned> EncodingIDs) const;
void emitInstrLenTable(formatted_raw_ostream &OS,
ArrayRef<unsigned> InstrLen) const;
void emitPredicateFunction(formatted_raw_ostream &OS,
PredicateSet &Predicates) const;
void emitDecoderFunction(formatted_raw_ostream &OS,
const DecoderSet &Decoders,
unsigned BucketBitWidth) const;
// run - Output the code emitter
void run(raw_ostream &o) const;
private:
void collectHwModesReferencedForEncodings(
std::vector<unsigned> &HwModeIDs,
NamespacesHwModesMap &NamespacesWithHwModes) const;
void
handleHwModesUnrelatedEncodings(unsigned EncodingID,
ArrayRef<unsigned> HwModeIDs,
NamespacesHwModesMap &NamespacesWithHwModes);
void parseInstructionEncodings();
};
} // end anonymous namespace
namespace {
/// Filter - Filter works with FilterChooser to produce the decoding tree for
/// the ISA.
///
/// It is useful to think of a Filter as governing the switch stmts of the
/// decoding tree in a certain level. Each case stmt delegates to an inferior
/// FilterChooser to decide what further decoding logic to employ, or in another
/// words, what other remaining bits to look at. The FilterChooser eventually
/// chooses a best Filter to do its job.
///
/// This recursive scheme ends when the number of Opcodes assigned to the
/// FilterChooser becomes 1 or if there is a conflict. A conflict happens when
/// the Filter/FilterChooser combo does not know how to distinguish among the
/// Opcodes assigned.
///
/// An example of a conflict is
///
/// Decoding Conflict:
/// ................................
/// 1111............................
/// 1111010.........................
/// 1111010...00....................
/// 1111010...00........0001........
/// 111101000.00........0001........
/// 111101000.00........00010000....
/// 111101000_00________00010000____ VST4q8a
/// 111101000_00________00010000____ VST4q8b
///
/// 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 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
/// decoder could try to decode the even/odd register numbering and assign to
/// VST4q8a or VST4q8b, but for the time being, the decoder chooses the "a"
/// version and return the Opcode since the two have the same Asm format string.
struct Filter {
unsigned StartBit; // the starting bit position
unsigned NumBits; // number of bits to filter
// Map of well-known segment value to the set of uid's with that value.
std::map<uint64_t, std::vector<unsigned>> FilteredIDs;
// Set of uid's with non-constant segment values.
std::vector<unsigned> VariableIDs;
Filter(ArrayRef<InstructionEncoding> Encodings,
ArrayRef<unsigned> EncodingIDs, unsigned StartBit, unsigned NumBits);
// Returns the number of fanout produced by the filter. More fanout implies
// the filter distinguishes more categories of instructions.
unsigned usefulness() const;
}; // end class Filter
// These are states of our finite state machines used in FilterChooser's
// filterProcessor() which produces the filter candidates to use.
enum bitAttr_t {
ATTR_NONE,
ATTR_FILTERED,
ATTR_ALL_SET,
ATTR_ALL_UNSET,
ATTR_MIXED
};
/// FilterChooser - FilterChooser chooses the best filter among a set of Filters
/// in order to perform the decoding of instructions at the current level.
///
/// Decoding proceeds from the top down. Based on the well-known encoding bits
/// of instructions available, FilterChooser builds up the possible Filters that
/// can further the task of decoding by distinguishing among the remaining
/// candidate instructions.
///
/// Once a filter has been chosen, it is called upon to divide the decoding task
/// into sub-tasks and delegates them to its inferior FilterChoosers for further
/// processings.
///
/// It is useful to think of a Filter as governing the switch stmts of the
/// decoding tree. And each case is delegated to an inferior FilterChooser to
/// decide what further remaining bits to look at.
class FilterChooser {
// TODO: Unfriend by providing the necessary accessors.
friend class DecoderTableBuilder;
// Vector of encodings to choose our filter.
ArrayRef<InstructionEncoding> Encodings;
/// Encoding IDs for this filter chooser to work on.
/// Sorted by non-decreasing encoding width.
SmallVector<unsigned, 0> EncodingIDs;
// Array of bit values passed down from our parent.
// Set to all unknown for Parent == nullptr.
KnownBits FilterBits;
// Links to the FilterChooser above us in the decoding tree.
const FilterChooser *Parent;
/// If the selected filter matches multiple encodings, then this is the
/// starting position and the width of the filtered range.
unsigned StartBit;
unsigned NumBits;
/// If the selected filter matches multiple encodings, and there is
/// *exactly one* encoding in which all bits are known in the filtered range,
/// then this is the ID of that encoding.
/// Also used when there is only one encoding.
std::optional<unsigned> SingletonEncodingID;
/// If the selected filter matches multiple encodings, and there is
/// *at least one* encoding in which all bits are known in the filtered range,
/// then this is the FilterChooser created for the subset of encodings that
/// contain some unknown bits in the filtered range.
std::unique_ptr<const FilterChooser> VariableFC;
/// If the selected filter matches multiple encodings, and there is
/// *more than one* encoding in which all bits are known in the filtered
/// range, then this is a map of field values to FilterChoosers created for
/// the subset of encodings sharing that field value.
/// The "field value" here refers to the encoding bits in the filtered range.
std::map<uint64_t, std::unique_ptr<const FilterChooser>> FilterChooserMap;
struct Island {
unsigned StartBit;
unsigned NumBits;
uint64_t FieldVal;
};
public:
/// Constructs a top-level filter chooser.
FilterChooser(ArrayRef<InstructionEncoding> Encodings,
ArrayRef<unsigned> EncodingIDs)
: Encodings(Encodings), EncodingIDs(EncodingIDs), Parent(nullptr) {
// Sort encoding IDs once.
stable_sort(this->EncodingIDs, LessEncodingIDByWidth(Encodings));
// Filter width is the width of the smallest encoding.
unsigned FilterWidth = Encodings[this->EncodingIDs.front()].getBitWidth();
FilterBits = KnownBits(FilterWidth);
doFilter();
}
/// Constructs an inferior filter chooser.
FilterChooser(ArrayRef<InstructionEncoding> Encodings,
ArrayRef<unsigned> EncodingIDs, const KnownBits &FilterBits,
const FilterChooser &Parent)
: Encodings(Encodings), EncodingIDs(EncodingIDs), Parent(&Parent) {
// Inferior filter choosers are created from sorted array of encoding IDs.
assert(is_sorted(EncodingIDs, LessEncodingIDByWidth(Encodings)));
assert(!FilterBits.hasConflict() && "Broken filter");
// Filter width is the width of the smallest encoding.
unsigned FilterWidth = Encodings[EncodingIDs.front()].getBitWidth();
this->FilterBits = FilterBits.anyext(FilterWidth);
doFilter();
}
FilterChooser(const FilterChooser &) = delete;
void operator=(const FilterChooser &) = delete;
/// Returns the width of the largest encoding.
unsigned getMaxEncodingWidth() const {
// The last encoding ID is the ID of an encoding with the largest width.
return Encodings[EncodingIDs.back()].getBitWidth();
}
private:
/// Applies the given filter to the set of encodings this FilterChooser
/// works with, creating inferior FilterChoosers as necessary.
void applyFilter(const Filter &F);
/// dumpStack - dumpStack traverses the filter chooser chain and calls
/// dumpFilterArray on each filter chooser up to the top level one.
void dumpStack(raw_ostream &OS, indent Indent, unsigned PadToWidth) const;
bool isPositionFiltered(unsigned Idx) const {
return FilterBits.Zero[Idx] || FilterBits.One[Idx];
}
// Calculates the island(s) needed to decode the instruction.
// This returns a list of undecoded bits of an instructions, for example,
// Inst{20} = 1 && Inst{3-0} == 0b1111 represents two islands of yet-to-be
// decoded bits in order to verify that the instruction matches the Opcode.
std::vector<Island> getIslands(const KnownBits &EncodingBits) const;
/// Scans the well-known encoding bits of the encodings and, builds up a list
/// of candidate filters, and then returns the best one, if any.
std::unique_ptr<Filter> findBestFilter(ArrayRef<bitAttr_t> BitAttrs,
bool AllowMixed,
bool Greedy = true) const;
std::unique_ptr<Filter> findBestFilter() const;
// Decides on the best configuration of filter(s) to use in order to decode
// the instructions. A conflict of instructions may occur, in which case we
// dump the conflict set to the standard error.
void doFilter();
public:
void dump() const;
};
class DecoderTableBuilder {
const CodeGenTarget &Target;
ArrayRef<InstructionEncoding> Encodings;
DecoderTableInfo &TableInfo;
public:
DecoderTableBuilder(const CodeGenTarget &Target,
ArrayRef<InstructionEncoding> Encodings,
DecoderTableInfo &TableInfo)
: Target(Target), Encodings(Encodings), TableInfo(TableInfo) {}
void buildTable(const FilterChooser &FC, unsigned BitWidth) const {
// When specializing decoders per bit width, each decoder table will begin
// with the bitwidth for that table.
if (SpecializeDecodersPerBitwidth)
TableInfo.Table.insertULEB128(BitWidth);
emitTableEntries(FC);
}
private:
void emitBinaryParser(raw_ostream &OS, indent Indent,
const OperandInfo &OpInfo) const;
void emitDecoder(raw_ostream &OS, indent Indent, unsigned EncodingID) const;
unsigned getDecoderIndex(unsigned EncodingID) const;
unsigned getPredicateIndex(StringRef P) const;
bool emitPredicateMatchAux(const Init &Val, bool ParenIfBinOp,
raw_ostream &OS) const;
bool emitPredicateMatch(raw_ostream &OS, unsigned EncodingID) const;
bool doesOpcodeNeedPredicate(unsigned EncodingID) const;
void emitPredicateTableEntry(unsigned EncodingID) const;
void emitSoftFailTableEntry(unsigned EncodingID) const;
void emitSingletonTableEntry(const FilterChooser &FC) const;
void emitTableEntries(const FilterChooser &FC) const;
};
} // end anonymous namespace
///////////////////////////
// //
// Filter Implementation //
// //
///////////////////////////
Filter::Filter(ArrayRef<InstructionEncoding> Encodings,
ArrayRef<unsigned> EncodingIDs, unsigned StartBit,
unsigned NumBits)
: StartBit(StartBit), NumBits(NumBits) {
for (unsigned EncodingID : EncodingIDs) {
const InstructionEncoding &Encoding = Encodings[EncodingID];
KnownBits EncodingBits = Encoding.getMandatoryBits();
// Scans the segment for possibly well-specified encoding bits.
KnownBits FieldBits = EncodingBits.extractBits(NumBits, StartBit);
if (FieldBits.isConstant()) {
// The encoding bits are well-known. Lets add the uid of the
// instruction into the bucket keyed off the constant field value.
FilteredIDs[FieldBits.getConstant().getZExtValue()].push_back(EncodingID);
} else {
// Some of the encoding bit(s) are unspecified. This contributes to
// one additional member of "Variable" instructions.
VariableIDs.push_back(EncodingID);
}
}
assert((FilteredIDs.size() + VariableIDs.size() > 0) &&
"Filter returns no instruction categories");
}
void FilterChooser::applyFilter(const Filter &F) {
StartBit = F.StartBit;
NumBits = F.NumBits;
assert(FilterBits.extractBits(NumBits, StartBit).isUnknown());
if (!F.VariableIDs.empty()) {
// Delegates to an inferior filter chooser for further processing on this
// group of instructions whose segment values are variable.
VariableFC = std::make_unique<FilterChooser>(Encodings, F.VariableIDs,
FilterBits, *this);
}
// Otherwise, create sub choosers.
for (const auto &[FilterVal, InferiorEncodingIDs] : F.FilteredIDs) {
// Create a new filter by inserting the field bits into the parent filter.
APInt FieldBits(NumBits, FilterVal);
KnownBits InferiorFilterBits = FilterBits;
InferiorFilterBits.insertBits(KnownBits::makeConstant(FieldBits), StartBit);
// Delegates to an inferior filter chooser for further processing on this
// category of instructions.
FilterChooserMap.try_emplace(FilterVal, std::make_unique<FilterChooser>(
Encodings, InferiorEncodingIDs,
InferiorFilterBits, *this));
}
}
// Returns the number of fanout produced by the filter. More fanout implies
// the filter distinguishes more categories of instructions.
unsigned Filter::usefulness() const {
return FilteredIDs.size() + VariableIDs.empty();
}
//////////////////////////////////
// //
// Filterchooser Implementation //
// //
//////////////////////////////////
// Emit the decoder state machine table. Returns a mask of MCD decoder ops
// that were emitted.
unsigned DecoderEmitter::emitTable(formatted_raw_ostream &OS,
DecoderTable &Table, StringRef Namespace,
unsigned HwModeID, unsigned BitWidth,
ArrayRef<unsigned> EncodingIDs) const {
// We'll need to be able to map from a decoded opcode into the corresponding
// EncodingID for this specific combination of BitWidth and Namespace. This
// is used below to index into Encodings.
DenseMap<unsigned, unsigned> OpcodeToEncodingID;
OpcodeToEncodingID.reserve(EncodingIDs.size());
for (unsigned EncodingID : EncodingIDs) {
const Record *InstDef = Encodings[EncodingID].getInstruction()->TheDef;
OpcodeToEncodingID[Target.getInstrIntValue(InstDef)] = EncodingID;
}
OS << "static const uint8_t DecoderTable" << Namespace;
if (HwModeID != DefaultMode)
OS << '_' << Target.getHwModes().getModeName(HwModeID);
OS << BitWidth << "[" << Table.size() << "] = {\n";
// Emit ULEB128 encoded value to OS, returning the number of bytes emitted.
auto emitULEB128 = [](DecoderTable::const_iterator &I,
formatted_raw_ostream &OS) {
while (*I >= 128)
OS << (unsigned)*I++ << ", ";
OS << (unsigned)*I++ << ", ";
};
// Emit `getNumToSkipInBytes()`-byte numtoskip value to OS, returning the
// NumToSkip value.
auto emitNumToSkip = [](DecoderTable::const_iterator &I,
formatted_raw_ostream &OS) {
uint8_t Byte = *I++;
uint32_t NumToSkip = Byte;
OS << (unsigned)Byte << ", ";
Byte = *I++;
OS << (unsigned)Byte << ", ";
NumToSkip |= Byte << 8;
if (getNumToSkipInBytes() == 3) {
Byte = *I++;
OS << (unsigned)(Byte) << ", ";
NumToSkip |= Byte << 16;
}
return NumToSkip;
};
// FIXME: We may be able to use the NumToSkip values to recover
// appropriate indentation levels.
DecoderTable::const_iterator I = Table.begin();
DecoderTable::const_iterator E = Table.end();
const uint8_t *const EndPtr = Table.data() + Table.size();
auto emitNumToSkipComment = [&](uint32_t NumToSkip, bool InComment = false) {
uint32_t Index = ((I - Table.begin()) + NumToSkip);
OS << (InComment ? ", " : "// ");
OS << "Skip to: " << Index;
};
// The first entry when specializing decoders per bitwidth is the bitwidth.
// This will be used for additional checks in `decodeInstruction`.
if (SpecializeDecodersPerBitwidth) {
OS << "/* 0 */";
OS.PadToColumn(14);
emitULEB128(I, OS);
OS << " // Bitwidth " << BitWidth << '\n';
}
unsigned OpcodeMask = 0;
while (I != E) {
assert(I < E && "incomplete decode table entry!");
uint64_t Pos = I - Table.begin();
OS << "/* " << Pos << " */";
OS.PadToColumn(12);
const uint8_t DecoderOp = *I++;
OpcodeMask |= (1 << DecoderOp);
switch (DecoderOp) {
default:
PrintFatalError("Invalid decode table opcode: " + Twine((int)DecoderOp) +
" at index " + Twine(Pos));
case MCD::OPC_Scope: {
OS << " MCD::OPC_Scope, ";
uint32_t NumToSkip = emitNumToSkip(I, OS);
emitNumToSkipComment(NumToSkip);
OS << '\n';
break;
}
case MCD::OPC_ExtractField: {
OS << " MCD::OPC_ExtractField, ";
// ULEB128 encoded start value.
const char *ErrMsg = nullptr;
unsigned Start = decodeULEB128(&*I, nullptr, EndPtr, &ErrMsg);
assert(ErrMsg == nullptr && "ULEB128 value too large!");
emitULEB128(I, OS);
unsigned Len = *I++;
OS << Len << ", // Inst{";
if (Len > 1)
OS << (Start + Len - 1) << "-";
OS << Start << "} ...\n";
break;
}
case MCD::OPC_FilterValueOrSkip: {
OS << " MCD::OPC_FilterValueOrSkip, ";
// The filter value is ULEB128 encoded.
emitULEB128(I, OS);
uint32_t NumToSkip = emitNumToSkip(I, OS);
emitNumToSkipComment(NumToSkip);
OS << '\n';
break;
}
case MCD::OPC_FilterValue: {
OS << " MCD::OPC_FilterValue, ";
// The filter value is ULEB128 encoded.
emitULEB128(I, OS);
OS << '\n';
break;
}
case MCD::OPC_CheckField: {
OS << " MCD::OPC_CheckField, ";
// ULEB128 encoded start value.
emitULEB128(I, OS);
// 8-bit length.
unsigned Len = *I++;
OS << Len << ", ";
// ULEB128 encoded field value.
emitULEB128(I, OS);
OS << '\n';
break;
}
case MCD::OPC_CheckPredicate: {
OS << " MCD::OPC_CheckPredicate, ";
emitULEB128(I, OS);
OS << '\n';
break;
}
case MCD::OPC_Decode:
case MCD::OPC_TryDecode: {
bool IsTry = DecoderOp == MCD::OPC_TryDecode;
// Decode the Opcode value.
const char *ErrMsg = nullptr;
unsigned Opc = decodeULEB128(&*I, nullptr, EndPtr, &ErrMsg);
assert(ErrMsg == nullptr && "ULEB128 value too large!");
OS << " MCD::OPC_" << (IsTry ? "Try" : "") << "Decode, ";
emitULEB128(I, OS);
// Decoder index.
unsigned DecodeIdx = decodeULEB128(&*I, nullptr, EndPtr, &ErrMsg);
assert(ErrMsg == nullptr && "ULEB128 value too large!");
emitULEB128(I, OS);
auto EncI = OpcodeToEncodingID.find(Opc);
assert(EncI != OpcodeToEncodingID.end() && "no encoding entry");
auto EncodingID = EncI->second;
if (!IsTry) {
OS << "// Opcode: " << Encodings[EncodingID].getName()
<< ", DecodeIdx: " << DecodeIdx << '\n';
break;
}
OS << '\n';
break;
}
case MCD::OPC_SoftFail: {
OS << " MCD::OPC_SoftFail, ";
// Decode the positive mask.
const char *ErrMsg = nullptr;
uint64_t PositiveMask = decodeULEB128(&*I, nullptr, EndPtr, &ErrMsg);
assert(ErrMsg == nullptr && "ULEB128 value too large!");
emitULEB128(I, OS);
// Decode the negative mask.
uint64_t NegativeMask = decodeULEB128(&*I, nullptr, EndPtr, &ErrMsg);
assert(ErrMsg == nullptr && "ULEB128 value too large!");
emitULEB128(I, OS);
OS << "// +ve mask: 0x";
OS.write_hex(PositiveMask);
OS << ", -ve mask: 0x";
OS.write_hex(NegativeMask);
OS << '\n';
break;
}
}
}
OS << "};\n\n";
return OpcodeMask;
}
void DecoderEmitter::emitInstrLenTable(formatted_raw_ostream &OS,
ArrayRef<unsigned> InstrLen) const {
OS << "static const uint8_t InstrLenTable[] = {\n";
for (unsigned Len : InstrLen)
OS << Len << ",\n";
OS << "};\n\n";
}
void DecoderEmitter::emitPredicateFunction(formatted_raw_ostream &OS,
PredicateSet &Predicates) const {
// The predicate function is just a big switch statement based on the
// input predicate index.
OS << "static bool checkDecoderPredicate(unsigned Idx, const FeatureBitset "
"&Bits) {\n";
OS << " switch (Idx) {\n";
OS << " default: llvm_unreachable(\"Invalid index!\");\n";
for (const auto &[Index, Predicate] : enumerate(Predicates)) {
OS << " case " << Index << ":\n";
OS << " return (" << Predicate << ");\n";
}
OS << " }\n";
OS << "}\n\n";
}
void DecoderEmitter::emitDecoderFunction(formatted_raw_ostream &OS,
const DecoderSet &Decoders,
unsigned BucketBitWidth) const {
// The decoder function is just a big switch statement or a table of function
// pointers based on the input decoder index.
// TODO: When InsnType is large, using uint64_t limits all fields to 64 bits
// It would be better for emitBinaryParser to use a 64-bit tmp whenever
// possible but fall back to an InsnType-sized tmp for truly large fields.
StringRef TmpTypeDecl =
"using TmpType = std::conditional_t<std::is_integral<InsnType>::value, "
"InsnType, uint64_t>;\n";
StringRef DecodeParams =
"DecodeStatus S, InsnType insn, MCInst &MI, uint64_t Address, const "
"MCDisassembler *Decoder, bool &DecodeComplete";
// Print the name of the decode function to OS.
auto PrintDecodeFnName = [&OS, BucketBitWidth](unsigned DecodeIdx) {
OS << "decodeFn";
if (BucketBitWidth != 0) {
OS << '_' << BucketBitWidth << "bit";
}
OS << '_' << DecodeIdx;
};
// Print the template statement.
auto PrintTemplate = [&OS, BucketBitWidth]() {
OS << "template <typename InsnType>\n";
OS << "static ";
if (BucketBitWidth != 0)
OS << "std::enable_if_t<InsnBitWidth<InsnType> == " << BucketBitWidth
<< ", DecodeStatus>\n";
else
OS << "DecodeStatus ";
};
if (UseFnTableInDecodeToMCInst) {
// Emit a function for each case first.
for (const auto &[Index, Decoder] : enumerate(Decoders)) {
PrintTemplate();
PrintDecodeFnName(Index);
OS << "(" << DecodeParams << ") {\n";
OS << " using namespace llvm::MCD;\n";
OS << " " << TmpTypeDecl;
OS << " [[maybe_unused]] TmpType tmp;\n";
OS << Decoder;
OS << " return S;\n";
OS << "}\n\n";
}
}
OS << "// Handling " << Decoders.size() << " cases.\n";
PrintTemplate();
OS << "decodeToMCInst(unsigned Idx, " << DecodeParams << ") {\n";
OS << " using namespace llvm::MCD;\n";
OS << " DecodeComplete = true;\n";
if (UseFnTableInDecodeToMCInst) {
// Build a table of function pointers
OS << " using DecodeFnTy = DecodeStatus (*)(" << DecodeParams << ");\n";
OS << " static constexpr DecodeFnTy decodeFnTable[] = {\n";
for (size_t Index : llvm::seq(Decoders.size())) {
OS << " ";
PrintDecodeFnName(Index);
OS << ",\n";
}
OS << " };\n";
OS << " if (Idx >= " << Decoders.size() << ")\n";
OS << " llvm_unreachable(\"Invalid decoder index!\");\n";
OS << " return decodeFnTable[Idx](S, insn, MI, Address, Decoder, "
"DecodeComplete);\n";
} else {
OS << " " << TmpTypeDecl;
OS << " TmpType tmp;\n";
OS << " switch (Idx) {\n";
OS << " default: llvm_unreachable(\"Invalid decoder index!\");\n";
for (const auto &[Index, Decoder] : enumerate(Decoders)) {
OS << " case " << Index << ":\n";
OS << Decoder;
OS << " return S;\n";
}
OS << " }\n";
}
OS << "}\n";
}
/// dumpStack - dumpStack traverses the filter chooser chain and calls
/// dumpFilterArray on each filter chooser up to the top level one.
void FilterChooser::dumpStack(raw_ostream &OS, indent Indent,
unsigned PadToWidth) const {
if (Parent)
Parent->dumpStack(OS, Indent, PadToWidth);
assert(PadToWidth >= FilterBits.getBitWidth());
OS << Indent << indent(PadToWidth - FilterBits.getBitWidth());
printKnownBits(OS, FilterBits, '.');
OS << '\n';
}
// Calculates the island(s) needed to decode the instruction.
// This returns a list of undecoded bits of an instructions, for example,
// Inst{20} = 1 && Inst{3-0} == 0b1111 represents two islands of yet-to-be
// decoded bits in order to verify that the instruction matches the Opcode.
std::vector<FilterChooser::Island>
FilterChooser::getIslands(const KnownBits &EncodingBits) const {
std::vector<Island> Islands;
uint64_t FieldVal;
unsigned StartBit;
// 0: Init
// 1: Water (the bit value does not affect decoding)
// 2: Island (well-known bit value needed for decoding)
unsigned State = 0;
unsigned FilterWidth = FilterBits.getBitWidth();
for (unsigned i = 0; i != FilterWidth; ++i) {
bool IsKnown = EncodingBits.Zero[i] || EncodingBits.One[i];
bool Filtered = isPositionFiltered(i);
switch (State) {
default:
llvm_unreachable("Unreachable code!");
case 0:
case 1:
if (Filtered || !IsKnown) {
State = 1; // Still in Water
} else {
State = 2; // Into the Island
StartBit = i;
FieldVal = static_cast<uint64_t>(EncodingBits.One[i]);
}
break;
case 2:
if (Filtered || !IsKnown) {
State = 1; // Into the Water
Islands.push_back({StartBit, i - StartBit, FieldVal});
} else {
State = 2; // Still in Island
FieldVal |= static_cast<uint64_t>(EncodingBits.One[i])
<< (i - StartBit);
}
break;
}
}
// If we are still in Island after the loop, do some housekeeping.
if (State == 2)
Islands.push_back({StartBit, FilterWidth - StartBit, FieldVal});
return Islands;
}
void DecoderTableBuilder::emitBinaryParser(raw_ostream &OS, indent Indent,
const OperandInfo &OpInfo) const {
// Special case for 'bits<0>'.
if (OpInfo.Fields.empty() && !OpInfo.InitValue) {
if (IgnoreNonDecodableOperands)
return;
assert(!OpInfo.Decoder.empty());
// The operand has no encoding, so the corresponding argument is omitted.
// This avoids confusion and allows the function to be overloaded if the
// operand does have an encoding in other instructions.
OS << Indent << "if (!Check(S, " << OpInfo.Decoder << "(MI, Decoder)))\n"
<< Indent << " return MCDisassembler::Fail;\n";
return;
}
if (OpInfo.Fields.empty() && OpInfo.InitValue && IgnoreFullyDefinedOperands)
return;
// We need to construct the encoding of the operand from pieces if it is not
// encoded sequentially or has a non-zero constant part in the encoding.
bool UseInsertBits = OpInfo.numFields() > 1 || OpInfo.InitValue.value_or(0);
if (UseInsertBits) {
OS << Indent << "tmp = 0x";
OS.write_hex(OpInfo.InitValue.value_or(0));
OS << ";\n";
}
for (const auto &[Base, Width, Offset] : OpInfo.fields()) {
OS << Indent;
if (UseInsertBits)
OS << "insertBits(tmp, ";
else
OS << "tmp = ";
OS << "fieldFromInstruction(insn, " << Base << ", " << Width << ')';
if (UseInsertBits)
OS << ", " << Offset << ", " << Width << ')';
else if (Offset != 0)
OS << " << " << Offset;
OS << ";\n";
}
StringRef Decoder = OpInfo.Decoder;
if (!Decoder.empty()) {
OS << Indent << "if (!Check(S, " << Decoder
<< "(MI, tmp, Address, Decoder))) { "
<< (OpInfo.HasCompleteDecoder ? "" : "DecodeComplete = false; ")
<< "return MCDisassembler::Fail; }\n";
} else {
OS << Indent << "MI.addOperand(MCOperand::createImm(tmp));\n";
}
}
void DecoderTableBuilder::emitDecoder(raw_ostream &OS, indent Indent,
unsigned EncodingID) const {
const InstructionEncoding &Encoding = Encodings[EncodingID];
// If a custom instruction decoder was specified, use that.
StringRef DecoderMethod = Encoding.getDecoderMethod();
if (!DecoderMethod.empty()) {
OS << Indent << "if (!Check(S, " << DecoderMethod
<< "(MI, insn, Address, Decoder))) { "
<< (Encoding.hasCompleteDecoder() ? "" : "DecodeComplete = false; ")
<< "return MCDisassembler::Fail; }\n";
return;
}
for (const OperandInfo &Op : Encoding.getOperands())
emitBinaryParser(OS, Indent, Op);
}
unsigned DecoderTableBuilder::getDecoderIndex(unsigned EncodingID) 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);
indent Indent(UseFnTableInDecodeToMCInst ? 2 : 4);
emitDecoder(S, Indent, EncodingID);
// Using the full decoder string as the key value here is a bit
// heavyweight, but is effective. If the string comparisons become a
// performance concern, we can implement a mangling of the predicate
// data easily enough with a map back to the actual string. That's
// overkill for now, though.
// Make sure the predicate is in the table.
DecoderSet &Decoders = TableInfo.Decoders;
Decoders.insert(CachedHashString(Decoder));
// Now figure out the index for when we write out the table.
DecoderSet::const_iterator P = find(Decoders, Decoder.str());
return std::distance(Decoders.begin(), P);
}
// If ParenIfBinOp is true, print a surrounding () if Val uses && or ||.
bool DecoderTableBuilder::emitPredicateMatchAux(const Init &Val,
bool ParenIfBinOp,
raw_ostream &OS) const {
if (const auto *D = dyn_cast<DefInit>(&Val)) {
if (!D->getDef()->isSubClassOf("SubtargetFeature"))
return true;
OS << "Bits[" << Target.getName() << "::" << D->getAsString() << "]";
return false;
}
if (const auto *D = dyn_cast<DagInit>(&Val)) {
std::string Op = D->getOperator()->getAsString();
if (Op == "not" && D->getNumArgs() == 1) {
OS << '!';
return emitPredicateMatchAux(*D->getArg(0), true, OS);
}
if ((Op == "any_of" || Op == "all_of") && D->getNumArgs() > 0) {
bool Paren = D->getNumArgs() > 1 && std::exchange(ParenIfBinOp, true);
if (Paren)
OS << '(';
ListSeparator LS(Op == "any_of" ? " || " : " && ");
for (auto *Arg : D->getArgs()) {
OS << LS;
if (emitPredicateMatchAux(*Arg, ParenIfBinOp, OS))
return true;
}
if (Paren)
OS << ')';
return false;
}
}
return true;
}
bool DecoderTableBuilder::emitPredicateMatch(raw_ostream &OS,
unsigned EncodingID) const {
const ListInit *Predicates =
Encodings[EncodingID].getRecord()->getValueAsListInit("Predicates");
bool IsFirstEmission = true;
for (unsigned i = 0; i < Predicates->size(); ++i) {
const Record *Pred = Predicates->getElementAsRecord(i);
if (!Pred->getValue("AssemblerMatcherPredicate"))
continue;
if (!isa<DagInit>(Pred->getValue("AssemblerCondDag")->getValue()))
continue;
if (!IsFirstEmission)
OS << " && ";
if (emitPredicateMatchAux(*Pred->getValueAsDag("AssemblerCondDag"),
Predicates->size() > 1, OS))
PrintFatalError(Pred->getLoc(), "Invalid AssemblerCondDag!");
IsFirstEmission = false;
}
return !Predicates->empty();
}
bool DecoderTableBuilder::doesOpcodeNeedPredicate(unsigned EncodingID) const {
const ListInit *Predicates =
Encodings[EncodingID].getRecord()->getValueAsListInit("Predicates");
for (unsigned i = 0; i < Predicates->size(); ++i) {
const Record *Pred = Predicates->getElementAsRecord(i);
if (!Pred->getValue("AssemblerMatcherPredicate"))
continue;
if (isa<DagInit>(Pred->getValue("AssemblerCondDag")->getValue()))
return true;
}
return false;
}
unsigned DecoderTableBuilder::getPredicateIndex(StringRef Predicate) const {
// Using the full predicate string as the key value here is a bit
// heavyweight, but is effective. If the string comparisons become a
// performance concern, we can implement a mangling of the predicate
// data easily enough with a map back to the actual string. That's
// overkill for now, though.
// Make sure the predicate is in the table.
TableInfo.Predicates.insert(CachedHashString(Predicate));
// Now figure out the index for when we write out the table.
PredicateSet::const_iterator P = find(TableInfo.Predicates, Predicate);
return (unsigned)(P - TableInfo.Predicates.begin());
}
void DecoderTableBuilder::emitPredicateTableEntry(unsigned EncodingID) const {
if (!doesOpcodeNeedPredicate(EncodingID))
return;
// Build up the predicate string.
SmallString<256> Predicate;
// FIXME: emitPredicateMatch() functions can take a buffer directly rather
// than a stream.
raw_svector_ostream PS(Predicate);
emitPredicateMatch(PS, EncodingID);
// Figure out the index into the predicate table for the predicate just
// computed.
unsigned PIdx = getPredicateIndex(PS.str());
TableInfo.Table.insertOpcode(MCD::OPC_CheckPredicate);
TableInfo.Table.insertULEB128(PIdx);
}
void DecoderTableBuilder::emitSoftFailTableEntry(unsigned EncodingID) const {
const InstructionEncoding &Encoding = Encodings[EncodingID];
const KnownBits &InstBits = Encoding.getInstBits();
const APInt &SoftFailMask = Encoding.getSoftFailMask();
if (SoftFailMask.isZero())
return;
APInt PositiveMask = InstBits.Zero & SoftFailMask;
APInt NegativeMask = InstBits.One & SoftFailMask;
TableInfo.Table.insertOpcode(MCD::OPC_SoftFail);
TableInfo.Table.insertULEB128(PositiveMask.getZExtValue());
TableInfo.Table.insertULEB128(NegativeMask.getZExtValue());
}
// Emits table entries to decode the singleton.
void DecoderTableBuilder::emitSingletonTableEntry(
const FilterChooser &FC) const {
unsigned EncodingID = *FC.SingletonEncodingID;
const InstructionEncoding &Encoding = Encodings[EncodingID];
KnownBits EncodingBits = Encoding.getMandatoryBits();
// Look for islands of undecoded bits of the singleton.
std::vector<FilterChooser::Island> Islands = FC.getIslands(EncodingBits);
// Emit the predicate table entry if one is needed.
emitPredicateTableEntry(EncodingID);
// Check any additional encoding fields needed.
for (const FilterChooser::Island &Ilnd : reverse(Islands)) {
TableInfo.Table.insertOpcode(MCD::OPC_CheckField);
TableInfo.Table.insertULEB128(Ilnd.StartBit);
TableInfo.Table.insertUInt8(Ilnd.NumBits);
TableInfo.Table.insertULEB128(Ilnd.FieldVal);
}
// Check for soft failure of the match.
emitSoftFailTableEntry(EncodingID);
unsigned DIdx = getDecoderIndex(EncodingID);
// 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.
const MCD::DecoderOps DecoderOp =
Encoding.hasCompleteDecoder() ? MCD::OPC_Decode : MCD::OPC_TryDecode;
TableInfo.Table.insertOpcode(DecoderOp);
const Record *InstDef = Encodings[EncodingID].getInstruction()->TheDef;
TableInfo.Table.insertULEB128(Target.getInstrIntValue(InstDef));
TableInfo.Table.insertULEB128(DIdx);
}
std::unique_ptr<Filter>
FilterChooser::findBestFilter(ArrayRef<bitAttr_t> BitAttrs, bool AllowMixed,
bool Greedy) const {
assert(EncodingIDs.size() >= 2 && "Nothing to filter");
// Heuristics. See also doFilter()'s "Heuristics" comment when num of
// instructions is 3.
if (AllowMixed && !Greedy) {
assert(EncodingIDs.size() == 3);
for (unsigned EncodingID : EncodingIDs) {
const InstructionEncoding &Encoding = Encodings[EncodingID];
KnownBits EncodingBits = Encoding.getMandatoryBits();
// Look for islands of undecoded bits of any instruction.
std::vector<Island> Islands = getIslands(EncodingBits);
if (!Islands.empty()) {
// Found an instruction with island(s). Now just assign a filter.
return std::make_unique<Filter>(
Encodings, EncodingIDs, Islands[0].StartBit, Islands[0].NumBits);
}
}
}
// The regionAttr automaton consumes the bitAttrs automatons' state,
// lowest-to-highest.
//
// Input symbols: F(iltered), (all_)S(et), (all_)U(nset), M(ixed)
// States: NONE, ALL_SET, MIXED
// Initial state: NONE
//
// (NONE) ----- F --> (NONE)
// (NONE) ----- S --> (ALL_SET) ; and set region start
// (NONE) ----- U --> (NONE)
// (NONE) ----- M --> (MIXED) ; and set region start
// (ALL_SET) -- F --> (NONE) ; and report an ALL_SET region
// (ALL_SET) -- S --> (ALL_SET)
// (ALL_SET) -- U --> (NONE) ; and report an ALL_SET region
// (ALL_SET) -- M --> (MIXED) ; and report an ALL_SET region
// (MIXED) ---- F --> (NONE) ; and report a MIXED region
// (MIXED) ---- S --> (ALL_SET) ; and report a MIXED region
// (MIXED) ---- U --> (NONE) ; and report a MIXED region
// (MIXED) ---- M --> (MIXED)
bitAttr_t RA = ATTR_NONE;
unsigned StartBit = 0;
std::vector<std::unique_ptr<Filter>> Filters;
auto addCandidateFilter = [&](unsigned StartBit, unsigned EndBit) {
Filters.push_back(std::make_unique<Filter>(Encodings, EncodingIDs, StartBit,
EndBit - StartBit));
};
unsigned FilterWidth = FilterBits.getBitWidth();
for (unsigned BitIndex = 0; BitIndex != FilterWidth; ++BitIndex) {
bitAttr_t bitAttr = BitAttrs[BitIndex];
assert(bitAttr != ATTR_NONE && "Bit without attributes");
switch (RA) {
case ATTR_NONE:
switch (bitAttr) {
case ATTR_FILTERED:
break;
case ATTR_ALL_SET:
StartBit = BitIndex;
RA = ATTR_ALL_SET;
break;
case ATTR_ALL_UNSET:
break;
case ATTR_MIXED:
StartBit = BitIndex;
RA = ATTR_MIXED;
break;
default:
llvm_unreachable("Unexpected bitAttr!");
}
break;
case ATTR_ALL_SET:
if (!AllowMixed && bitAttr != ATTR_ALL_SET)
addCandidateFilter(StartBit, BitIndex);
switch (bitAttr) {
case ATTR_FILTERED:
RA = ATTR_NONE;
break;
case ATTR_ALL_SET:
break;
case ATTR_ALL_UNSET:
RA = ATTR_NONE;
break;
case ATTR_MIXED:
StartBit = BitIndex;
RA = ATTR_MIXED;
break;
default:
llvm_unreachable("Unexpected bitAttr!");
}
break;
case ATTR_MIXED:
if (AllowMixed && bitAttr != ATTR_MIXED)
addCandidateFilter(StartBit, BitIndex);
switch (bitAttr) {
case ATTR_FILTERED:
StartBit = BitIndex;
RA = ATTR_NONE;
break;
case ATTR_ALL_SET:
StartBit = BitIndex;
RA = ATTR_ALL_SET;
break;
case ATTR_ALL_UNSET:
RA = ATTR_NONE;
break;
case ATTR_MIXED:
break;
default:
llvm_unreachable("Unexpected bitAttr!");
}
break;
case ATTR_ALL_UNSET:
llvm_unreachable("regionAttr state machine has no ATTR_UNSET state");
case ATTR_FILTERED:
llvm_unreachable("regionAttr state machine has no ATTR_FILTERED state");
}
}
// At the end, if we're still in ALL_SET or MIXED states, report a region
switch (RA) {
case ATTR_NONE:
break;
case ATTR_FILTERED:
break;
case ATTR_ALL_SET:
if (!AllowMixed)
addCandidateFilter(StartBit, FilterWidth);
break;
case ATTR_ALL_UNSET:
break;
case ATTR_MIXED:
if (AllowMixed)
addCandidateFilter(StartBit, FilterWidth);
break;
}
// We have finished with the filter processings. Now it's time to choose
// the best performing filter.
auto MaxIt = llvm::max_element(Filters, [](const std::unique_ptr<Filter> &A,
const std::unique_ptr<Filter> &B) {
return A->usefulness() < B->usefulness();
});
if (MaxIt == Filters.end() || (*MaxIt)->usefulness() == 0)
return nullptr;
return std::move(*MaxIt);
}
std::unique_ptr<Filter> FilterChooser::findBestFilter() const {
// We maintain BIT_WIDTH copies of the bitAttrs automaton.
// The automaton consumes the corresponding bit from each
// instruction.
//
// Input symbols: 0, 1, _ (unset), and . (any of the above).
// States: NONE, FILTERED, ALL_SET, ALL_UNSET, and MIXED.
// Initial state: NONE.
//
// (NONE) ------- [01] -> (ALL_SET)
// (NONE) ------- _ ----> (ALL_UNSET)
// (ALL_SET) ---- [01] -> (ALL_SET)
// (ALL_SET) ---- _ ----> (MIXED)
// (ALL_UNSET) -- [01] -> (MIXED)
// (ALL_UNSET) -- _ ----> (ALL_UNSET)
// (MIXED) ------ . ----> (MIXED)
// (FILTERED)---- . ----> (FILTERED)
unsigned FilterWidth = FilterBits.getBitWidth();
SmallVector<bitAttr_t, 128> BitAttrs(FilterWidth, ATTR_NONE);
// FILTERED bit positions provide no entropy and are not worthy of pursuing.
// Filter::recurse() set either 1 or 0 for each position.
for (unsigned BitIndex = 0; BitIndex != FilterWidth; ++BitIndex)
if (isPositionFiltered(BitIndex))
BitAttrs[BitIndex] = ATTR_FILTERED;
for (unsigned EncodingID : EncodingIDs) {
const InstructionEncoding &Encoding = Encodings[EncodingID];
KnownBits EncodingBits = Encoding.getMandatoryBits();
for (unsigned BitIndex = 0; BitIndex != FilterWidth; ++BitIndex) {
bool IsKnown = EncodingBits.Zero[BitIndex] || EncodingBits.One[BitIndex];
switch (BitAttrs[BitIndex]) {
case ATTR_NONE:
if (IsKnown)
BitAttrs[BitIndex] = ATTR_ALL_SET;
else
BitAttrs[BitIndex] = ATTR_ALL_UNSET;
break;
case ATTR_ALL_SET:
if (!IsKnown)
BitAttrs[BitIndex] = ATTR_MIXED;
break;
case ATTR_ALL_UNSET:
if (IsKnown)
BitAttrs[BitIndex] = ATTR_MIXED;
break;
case ATTR_MIXED:
case ATTR_FILTERED:
break;
}
}
}
// Try regions of consecutive known bit values first.
if (std::unique_ptr<Filter> F =
findBestFilter(BitAttrs, /*AllowMixed=*/false))
return F;
// Then regions of mixed bits (both known and unitialized bit values allowed).
if (std::unique_ptr<Filter> F = findBestFilter(BitAttrs, /*AllowMixed=*/true))
return F;
// Heuristics to cope with conflict set {t2CMPrs, t2SUBSrr, t2SUBSrs} where
// no single instruction for the maximum ATTR_MIXED region Inst{14-4} has a
// well-known encoding pattern. In such case, we backtrack and scan for the
// the very first consecutive ATTR_ALL_SET region and assign a filter to it.
if (EncodingIDs.size() == 3) {
if (std::unique_ptr<Filter> F =
findBestFilter(BitAttrs, /*AllowMixed=*/true, /*Greedy=*/false))
return F;
}
// There is a conflict we could not resolve.
return nullptr;
}
// Decides on the best configuration of filter(s) to use in order to decode
// the instructions. A conflict of instructions may occur, in which case we
// dump the conflict set to the standard error.
void FilterChooser::doFilter() {
assert(!EncodingIDs.empty() && "FilterChooser created with no instructions");
// No filter needed.
if (EncodingIDs.size() == 1) {
SingletonEncodingID = EncodingIDs.front();
return;
}
std::unique_ptr<Filter> BestFilter = findBestFilter();
if (BestFilter) {
applyFilter(*BestFilter);
return;
}
// Print out useful conflict information for postmortem analysis.
errs() << "Decoding Conflict:\n";
dump();
PrintFatalError("Decoding conflict encountered");
}
void FilterChooser::dump() const {
indent Indent(4);
// Helps to keep the output right-justified.
unsigned PadToWidth = getMaxEncodingWidth();
// Dump filter stack.
dumpStack(errs(), Indent, PadToWidth);
// Dump encodings.
for (unsigned EncodingID : EncodingIDs) {
const InstructionEncoding &Encoding = Encodings[EncodingID];
errs() << Indent << indent(PadToWidth - Encoding.getBitWidth());
printKnownBits(errs(), Encoding.getMandatoryBits(), '_');
errs() << " " << Encoding.getName() << '\n';
}
}
void DecoderTableBuilder::emitTableEntries(const FilterChooser &FC) const {
DecoderTable &Table = TableInfo.Table;
// If there are other encodings that could match if those with all bits
// known don't, enter a scope so that they have a chance.
size_t FixupLoc = 0;
if (FC.VariableFC) {
Table.insertOpcode(MCD::OPC_Scope);
FixupLoc = Table.insertNumToSkip();
}
if (FC.SingletonEncodingID) {
assert(FC.FilterChooserMap.empty());
// There is only one encoding in which all bits in the filtered range are
// fully defined, but we still need to check if the remaining (unfiltered)
// bits are valid for this encoding. We also need to check predicates etc.
emitSingletonTableEntry(FC);
} else if (FC.FilterChooserMap.size() == 1) {
// If there is only one possible field value, emit a combined OPC_CheckField
// instead of OPC_ExtractField + OPC_FilterValue.
const auto &[FilterVal, Delegate] = *FC.FilterChooserMap.begin();
Table.insertOpcode(MCD::OPC_CheckField);
Table.insertULEB128(FC.StartBit);
Table.insertUInt8(FC.NumBits);
Table.insertULEB128(FilterVal);
// Emit table entries for the only case.
emitTableEntries(*Delegate);
} else {
// The general case: emit a switch over the field value.
Table.insertOpcode(MCD::OPC_ExtractField);
Table.insertULEB128(FC.StartBit);
Table.insertUInt8(FC.NumBits);
// Emit switch cases for all but the last element.
for (const auto &[FilterVal, Delegate] : drop_end(FC.FilterChooserMap)) {
Table.insertOpcode(MCD::OPC_FilterValueOrSkip);
Table.insertULEB128(FilterVal);
size_t FixupPos = Table.insertNumToSkip();
// Emit table entries for this case.
emitTableEntries(*Delegate);
// Patch the previous FilterValueOrSkip to fall through to the next case.
Table.patchNumToSkip(FixupPos, Table.size());
}
// Emit a switch case for the last element. It never falls through;
// if it doesn't match, we leave the current scope.
const auto &[FilterVal, Delegate] = *FC.FilterChooserMap.rbegin();
Table.insertOpcode(MCD::OPC_FilterValue);
Table.insertULEB128(FilterVal);
// Emit table entries for the last case.
emitTableEntries(*Delegate);
}
if (FC.VariableFC) {
Table.patchNumToSkip(FixupLoc, Table.size());
emitTableEntries(*FC.VariableFC);
}
}
static std::string findOperandDecoderMethod(const Record *Record) {
std::string Decoder;
const RecordVal *DecoderString = Record->getValue("DecoderMethod");
const StringInit *String =
DecoderString ? dyn_cast<StringInit>(DecoderString->getValue()) : nullptr;
if (String) {
Decoder = String->getValue().str();
if (!Decoder.empty())
return Decoder;
}
if (Record->isSubClassOf("RegisterOperand"))
// Allows use of a DecoderMethod in referenced RegisterClass if set.
return findOperandDecoderMethod(Record->getValueAsDef("RegClass"));
if (Record->isSubClassOf("RegisterClass")) {
Decoder = "Decode" + Record->getName().str() + "RegisterClass";
} else if (Record->isSubClassOf("PointerLikeRegClass")) {
Decoder = "DecodePointerLikeRegClass" +
utostr(Record->getValueAsInt("RegClassKind"));
}
return Decoder;
}
OperandInfo getOpInfo(const Record *TypeRecord) {
const RecordVal *HasCompleteDecoderVal =
TypeRecord->getValue("hasCompleteDecoder");
const BitInit *HasCompleteDecoderBit =
HasCompleteDecoderVal
? dyn_cast<BitInit>(HasCompleteDecoderVal->getValue())
: nullptr;
bool HasCompleteDecoder =
HasCompleteDecoderBit ? HasCompleteDecoderBit->getValue() : true;
return OperandInfo(findOperandDecoderMethod(TypeRecord), HasCompleteDecoder);
}
void InstructionEncoding::parseVarLenEncoding(const VarLenInst &VLI) {
InstBits = KnownBits(VLI.size());
SoftFailMask = APInt(VLI.size(), 0);
// Parse Inst field.
unsigned I = 0;
for (const EncodingSegment &S : VLI) {
if (const auto *SegmentBits = dyn_cast<BitsInit>(S.Value)) {
for (const Init *V : SegmentBits->getBits()) {
if (const auto *B = dyn_cast<BitInit>(V)) {
if (B->getValue())
InstBits.One.setBit(I);
else
InstBits.Zero.setBit(I);
}
++I;
}
} else if (const auto *B = dyn_cast<BitInit>(S.Value)) {
if (B->getValue())
InstBits.One.setBit(I);
else
InstBits.Zero.setBit(I);
++I;
} else {
I += S.BitWidth;
}
}
assert(I == VLI.size());
}
void InstructionEncoding::parseFixedLenEncoding(
const BitsInit &RecordInstBits) {
// For fixed length instructions, sometimes the `Inst` field specifies more
// bits than the actual size of the instruction, which is specified in `Size`.
// In such cases, we do some basic validation and drop the upper bits.
unsigned BitWidth = EncodingDef->getValueAsInt("Size") * 8;
unsigned InstNumBits = RecordInstBits.getNumBits();
// Returns true if all bits in `Bits` are zero or unset.
auto CheckAllZeroOrUnset = [&](ArrayRef<const Init *> Bits,
const RecordVal *Field) {
bool AllZeroOrUnset = llvm::all_of(Bits, [](const Init *Bit) {
if (const auto *BI = dyn_cast<BitInit>(Bit))
return !BI->getValue();
return isa<UnsetInit>(Bit);
});
if (AllZeroOrUnset)
return;
PrintNote([Field](raw_ostream &OS) { Field->print(OS); });
PrintFatalError(EncodingDef, Twine(Name) + ": Size is " + Twine(BitWidth) +
" bits, but " + Field->getName() +
" bits beyond that are not zero/unset");
};
if (InstNumBits < BitWidth)
PrintFatalError(EncodingDef, Twine(Name) + ": Size is " + Twine(BitWidth) +
" bits, but Inst specifies only " +
Twine(InstNumBits) + " bits");
if (InstNumBits > BitWidth) {
// Ensure that all the bits beyond 'Size' are 0 or unset (i.e., carry no
// actual encoding).
ArrayRef<const Init *> UpperBits =
RecordInstBits.getBits().drop_front(BitWidth);
const RecordVal *InstField = EncodingDef->getValue("Inst");
CheckAllZeroOrUnset(UpperBits, InstField);
}
ArrayRef<const Init *> ActiveInstBits =
RecordInstBits.getBits().take_front(BitWidth);
InstBits = KnownBits(BitWidth);
SoftFailMask = APInt(BitWidth, 0);
// Parse Inst field.
for (auto [I, V] : enumerate(ActiveInstBits)) {
if (const auto *B = dyn_cast<BitInit>(V)) {
if (B->getValue())
InstBits.One.setBit(I);
else
InstBits.Zero.setBit(I);
}
}
// Parse SoftFail field.
const RecordVal *SoftFailField = EncodingDef->getValue("SoftFail");
if (!SoftFailField)
return;
const auto *SFBits = dyn_cast<BitsInit>(SoftFailField->getValue());
if (!SFBits || SFBits->getNumBits() != InstNumBits) {
PrintNote(EncodingDef->getLoc(), "in record");
PrintFatalError(SoftFailField,
formatv("SoftFail field, if defined, must be "
"of the same type as Inst, which is bits<{}>",
InstNumBits));
}
if (InstNumBits > BitWidth) {
// Ensure that all upper bits of `SoftFail` are 0 or unset.
ArrayRef<const Init *> UpperBits = SFBits->getBits().drop_front(BitWidth);
CheckAllZeroOrUnset(UpperBits, SoftFailField);
}
ArrayRef<const Init *> ActiveSFBits = SFBits->getBits().take_front(BitWidth);
for (auto [I, V] : enumerate(ActiveSFBits)) {
if (const auto *B = dyn_cast<BitInit>(V); B && B->getValue()) {
if (!InstBits.Zero[I] && !InstBits.One[I]) {
PrintNote(EncodingDef->getLoc(), "in record");
PrintError(SoftFailField,
formatv("SoftFail{{{0}} = 1 requires Inst{{{0}} "
"to be fully defined (0 or 1, not '?')",
I));
}
SoftFailMask.setBit(I);
}
}
}
void InstructionEncoding::parseVarLenOperands(const VarLenInst &VLI) {
SmallVector<int> TiedTo;
for (const auto &[Idx, Op] : enumerate(Inst->Operands)) {
if (Op.MIOperandInfo && Op.MIOperandInfo->getNumArgs() > 0)
for (auto *Arg : Op.MIOperandInfo->getArgs())
Operands.push_back(getOpInfo(cast<DefInit>(Arg)->getDef()));
else
Operands.push_back(getOpInfo(Op.Rec));
int TiedReg = Op.getTiedRegister();
TiedTo.push_back(-1);
if (TiedReg != -1) {
TiedTo[Idx] = TiedReg;
TiedTo[TiedReg] = Idx;
}
}
unsigned CurrBitPos = 0;
for (const auto &EncodingSegment : VLI) {
unsigned Offset = 0;
StringRef OpName;
if (const StringInit *SI = dyn_cast<StringInit>(EncodingSegment.Value)) {
OpName = SI->getValue();
} else if (const DagInit *DI = dyn_cast<DagInit>(EncodingSegment.Value)) {
OpName = cast<StringInit>(DI->getArg(0))->getValue();
Offset = cast<IntInit>(DI->getArg(2))->getValue();
}
if (!OpName.empty()) {
auto OpSubOpPair = Inst->Operands.parseOperandName(OpName);
unsigned OpIdx = Inst->Operands.getFlattenedOperandNumber(OpSubOpPair);
Operands[OpIdx].addField(CurrBitPos, EncodingSegment.BitWidth, Offset);
if (!EncodingSegment.CustomDecoder.empty())
Operands[OpIdx].Decoder = EncodingSegment.CustomDecoder.str();
int TiedReg = TiedTo[OpSubOpPair.first];
if (TiedReg != -1) {
unsigned OpIdx = Inst->Operands.getFlattenedOperandNumber(
{TiedReg, OpSubOpPair.second});
Operands[OpIdx].addField(CurrBitPos, EncodingSegment.BitWidth, Offset);
}
}
CurrBitPos += EncodingSegment.BitWidth;
}
}
static void debugDumpRecord(const Record &Rec) {
// Dump the record, so we can see what's going on.
PrintNote([&Rec](raw_ostream &OS) {
OS << "Dumping record for previous error:\n";
OS << Rec;
});
}
/// For an operand field named OpName: populate OpInfo.InitValue with the
/// constant-valued bit values, and OpInfo.Fields with the ranges of bits to
/// insert from the decoded instruction.
static void addOneOperandFields(const Record *EncodingDef,
const BitsInit &InstBits,
std::map<StringRef, StringRef> &TiedNames,
const Record *OpRec, StringRef OpName,
OperandInfo &OpInfo) {
// Find a field with the operand's name.
const RecordVal *OpEncodingField = EncodingDef->getValue(OpName);
// If there is no such field, try tied operand's name.
if (!OpEncodingField) {
if (auto I = TiedNames.find(OpName); I != TiedNames.end())
OpEncodingField = EncodingDef->getValue(I->second);
// If still no luck, the old behavior is to not decode this operand
// automatically and let the target do it. This is error-prone, so
// the new behavior is to report an error.
if (!OpEncodingField) {
if (!IgnoreNonDecodableOperands)
PrintError(EncodingDef->getLoc(),
"could not find field for operand '" + OpName + "'");
return;
}
}
// Some or all bits of the operand may be required to be 0 or 1 depending
// on the instruction's encoding. Collect those bits.
if (const auto *OpBit = dyn_cast<BitInit>(OpEncodingField->getValue())) {
OpInfo.InitValue = OpBit->getValue();
return;
}
if (const auto *OpBits = dyn_cast<BitsInit>(OpEncodingField->getValue())) {
if (OpBits->getNumBits() == 0) {
if (OpInfo.Decoder.empty()) {
PrintError(EncodingDef->getLoc(), "operand '" + OpName + "' of type '" +
OpRec->getName() +
"' must have a decoder method");
}
return;
}
for (unsigned I = 0; I < OpBits->getNumBits(); ++I) {
if (const auto *OpBit = dyn_cast<BitInit>(OpBits->getBit(I)))
OpInfo.InitValue = OpInfo.InitValue.value_or(0) |
static_cast<uint64_t>(OpBit->getValue()) << I;
}
}
// Find out where the variable bits of the operand are encoded. The bits don't
// have to be consecutive or in ascending order. For example, an operand could
// be encoded as follows:
//
// 7 6 5 4 3 2 1 0
// {1, op{5}, op{2}, op{1}, 0, op{4}, op{3}, ?}
//
// In this example the operand is encoded in three segments:
//
// Base Width Offset
// op{2...1} 4 2 1
// op{4...3} 1 2 3
// op{5} 6 1 5
//
for (unsigned I = 0, J = 0; I != InstBits.getNumBits(); I = J) {
const VarInit *Var;
unsigned Offset = 0;
for (; J != InstBits.getNumBits(); ++J) {
const Init *BitJ = InstBits.getBit(J);
if (const auto *VBI = dyn_cast<VarBitInit>(BitJ)) {
Var = dyn_cast<VarInit>(VBI->getBitVar());
if (I == J)
Offset = VBI->getBitNum();
else if (VBI->getBitNum() != Offset + J - I)
break;
} else {
Var = dyn_cast<VarInit>(BitJ);
}
if (!Var ||
(Var->getName() != OpName && Var->getName() != TiedNames[OpName]))
break;
}
if (I == J)
++J;
else
OpInfo.addField(I, J - I, Offset);
}
}
void InstructionEncoding::parseFixedLenOperands(const BitsInit &Bits) {
// Search for tied operands, so that we can correctly instantiate
// operands that are not explicitly represented in the encoding.
std::map<StringRef, StringRef> TiedNames;
for (const auto &Op : Inst->Operands) {
for (const auto &[J, CI] : enumerate(Op.Constraints)) {
if (!CI.isTied())
continue;
std::pair<unsigned, unsigned> SO =
Inst->Operands.getSubOperandNumber(CI.getTiedOperand());
StringRef TiedName = Inst->Operands[SO.first].SubOpNames[SO.second];
if (TiedName.empty())
TiedName = Inst->Operands[SO.first].Name;
StringRef MyName = Op.SubOpNames[J];
if (MyName.empty())
MyName = Op.Name;
TiedNames[MyName] = TiedName;
TiedNames[TiedName] = MyName;
}
}
// For each operand, see if we can figure out where it is encoded.
for (const CGIOperandList::OperandInfo &Op : Inst->Operands) {
// Lookup the decoder method and construct a new OperandInfo to hold our
// result.
OperandInfo OpInfo = getOpInfo(Op.Rec);
// If we have named sub-operands...
if (Op.MIOperandInfo && !Op.SubOpNames[0].empty()) {
// Then there should not be a custom decoder specified on the top-level
// type.
if (!OpInfo.Decoder.empty()) {
PrintError(EncodingDef,
"DecoderEmitter: operand \"" + Op.Name + "\" has type \"" +
Op.Rec->getName() +
"\" with a custom DecoderMethod, but also named "
"sub-operands.");
continue;
}
// Decode each of the sub-ops separately.
for (auto [SubOpName, SubOp] :
zip_equal(Op.SubOpNames, Op.MIOperandInfo->getArgs())) {
const Record *SubOpRec = cast<DefInit>(SubOp)->getDef();
OperandInfo SubOpInfo = getOpInfo(SubOpRec);
addOneOperandFields(EncodingDef, Bits, TiedNames, SubOpRec, SubOpName,
SubOpInfo);
Operands.push_back(std::move(SubOpInfo));
}
continue;
}
// Otherwise, if we have an operand with sub-operands, but they aren't
// named...
if (Op.MIOperandInfo && OpInfo.Decoder.empty()) {
// If we have sub-ops, we'd better have a custom decoder.
// (Otherwise we don't know how to populate them properly...)
if (Op.MIOperandInfo->getNumArgs()) {
PrintError(EncodingDef,
"DecoderEmitter: operand \"" + Op.Name +
"\" has non-empty MIOperandInfo, but doesn't "
"have a custom decoder!");
debugDumpRecord(*EncodingDef);
continue;
}
}
addOneOperandFields(EncodingDef, Bits, TiedNames, Op.Rec, Op.Name, OpInfo);
Operands.push_back(std::move(OpInfo));
}
}
InstructionEncoding::InstructionEncoding(const Record *EncodingDef,
const CodeGenInstruction *Inst)
: EncodingDef(EncodingDef), Inst(Inst) {
const Record *InstDef = Inst->TheDef;
// Give this encoding a name.
if (EncodingDef != InstDef)
Name = (EncodingDef->getName() + Twine(':')).str();
Name.append(InstDef->getName());
DecoderNamespace = EncodingDef->getValueAsString("DecoderNamespace");
DecoderMethod = EncodingDef->getValueAsString("DecoderMethod");
if (!DecoderMethod.empty())
HasCompleteDecoder = EncodingDef->getValueAsBit("hasCompleteDecoder");
const RecordVal *InstField = EncodingDef->getValue("Inst");
if (const auto *DI = dyn_cast<DagInit>(InstField->getValue())) {
VarLenInst VLI(DI, InstField);
parseVarLenEncoding(VLI);
// If the encoding has a custom decoder, don't bother parsing the operands.
if (DecoderMethod.empty())
parseVarLenOperands(VLI);
} else {
const auto *BI = cast<BitsInit>(InstField->getValue());
parseFixedLenEncoding(*BI);
// If the encoding has a custom decoder, don't bother parsing the operands.
if (DecoderMethod.empty())
parseFixedLenOperands(*BI);
}
if (DecoderMethod.empty()) {
// A generated decoder is always successful if none of the operand
// decoders can fail (all are always successful).
HasCompleteDecoder = all_of(Operands, [](const OperandInfo &Op) {
// By default, a generated operand decoder is assumed to always succeed.
// This can be overridden by the user.
return Op.Decoder.empty() || Op.HasCompleteDecoder;
});
}
}
// emitDecodeInstruction - Emit the templated helper function
// decodeInstruction().
static void emitDecodeInstruction(formatted_raw_ostream &OS, bool IsVarLenInst,
unsigned OpcodeMask) {
const bool HasTryDecode = OpcodeMask & (1 << MCD::OPC_TryDecode);
const bool HasCheckPredicate = OpcodeMask & (1 << MCD::OPC_CheckPredicate);
const bool HasSoftFail = OpcodeMask & (1 << MCD::OPC_SoftFail);
OS << R"(
static unsigned decodeNumToSkip(const uint8_t *&Ptr) {
unsigned NumToSkip = *Ptr++;
NumToSkip |= (*Ptr++) << 8;
)";
if (getNumToSkipInBytes() == 3)
OS << " NumToSkip |= (*Ptr++) << 16;\n";
OS << R"( return NumToSkip;
}
template <typename InsnType>
static DecodeStatus decodeInstruction(const uint8_t DecodeTable[], MCInst &MI,
InsnType insn, uint64_t Address,
const MCDisassembler *DisAsm,
const MCSubtargetInfo &STI)";
if (IsVarLenInst) {
OS << ",\n "
"llvm::function_ref<void(APInt &, uint64_t)> makeUp";
}
OS << ") {\n";
if (HasCheckPredicate)
OS << " const FeatureBitset &Bits = STI.getFeatureBits();\n";
OS << " using namespace llvm::MCD;\n";
OS << " const uint8_t *Ptr = DecodeTable;\n";
if (SpecializeDecodersPerBitwidth) {
// Fail with a fatal error if decoder table's bitwidth does not match
// `InsnType` bitwidth.
OS << R"(
[[maybe_unused]] uint32_t BitWidth = decodeULEB128AndIncUnsafe(Ptr);
assert(InsnBitWidth<InsnType> == BitWidth &&
"Table and instruction bitwidth mismatch");
)";
}
OS << R"(
SmallVector<const uint8_t *, 8> ScopeStack;
uint64_t CurFieldValue = 0;
DecodeStatus S = MCDisassembler::Success;
while (true) {
ptrdiff_t Loc = Ptr - DecodeTable;
const uint8_t DecoderOp = *Ptr++;
switch (DecoderOp) {
default:
errs() << Loc << ": Unexpected decode table opcode: "
<< (int)DecoderOp << '\n';
return MCDisassembler::Fail;
case MCD::OPC_Scope: {
unsigned NumToSkip = decodeNumToSkip(Ptr);
const uint8_t *SkipTo = Ptr + NumToSkip;
ScopeStack.push_back(SkipTo);
LLVM_DEBUG(dbgs() << Loc << ": OPC_Scope(" << SkipTo - DecodeTable
<< ")\n");
break;
}
case MCD::OPC_ExtractField: {
// Decode the start value.
unsigned Start = decodeULEB128AndIncUnsafe(Ptr);
unsigned Len = *Ptr++;)";
if (IsVarLenInst)
OS << "\n makeUp(insn, Start + Len);";
OS << R"(
CurFieldValue = fieldFromInstruction(insn, Start, Len);
LLVM_DEBUG(dbgs() << Loc << ": OPC_ExtractField(" << Start << ", "
<< Len << "): " << CurFieldValue << "\n");
break;
}
case MCD::OPC_FilterValueOrSkip: {
// Decode the field value.
uint64_t Val = decodeULEB128AndIncUnsafe(Ptr);
bool Failed = Val != CurFieldValue;
unsigned NumToSkip = decodeNumToSkip(Ptr);
const uint8_t *SkipTo = Ptr + NumToSkip;
LLVM_DEBUG(dbgs() << Loc << ": OPC_FilterValueOrSkip(" << Val << ", "
<< SkipTo - DecodeTable << ") "
<< (Failed ? "FAIL, " : "PASS\n"));
if (Failed) {
Ptr = SkipTo;
LLVM_DEBUG(dbgs() << "continuing at " << Ptr - DecodeTable << '\n');
}
break;
}
case MCD::OPC_FilterValue: {
// Decode the field value.
uint64_t Val = decodeULEB128AndIncUnsafe(Ptr);
bool Failed = Val != CurFieldValue;
LLVM_DEBUG(dbgs() << Loc << ": OPC_FilterValue(" << Val << ") "
<< (Failed ? "FAIL, " : "PASS\n"));
if (Failed) {
if (ScopeStack.empty()) {
LLVM_DEBUG(dbgs() << "returning Fail\n");
return MCDisassembler::Fail;
}
Ptr = ScopeStack.pop_back_val();
LLVM_DEBUG(dbgs() << "continuing at " << Ptr - DecodeTable << '\n');
}
break;
}
case MCD::OPC_CheckField: {
// Decode the start value.
unsigned Start = decodeULEB128AndIncUnsafe(Ptr);
unsigned Len = *Ptr;)";
if (IsVarLenInst)
OS << "\n makeUp(insn, Start + Len);";
OS << R"(
uint64_t FieldValue = fieldFromInstruction(insn, Start, Len);
// Decode the field value.
unsigned PtrLen = 0;
uint64_t ExpectedValue = decodeULEB128(++Ptr, &PtrLen);
Ptr += PtrLen;
bool Failed = ExpectedValue != FieldValue;
LLVM_DEBUG(dbgs() << Loc << ": OPC_CheckField(" << Start << ", " << Len
<< ", " << ExpectedValue << "): FieldValue = "
<< FieldValue << ", ExpectedValue = " << ExpectedValue
<< ": " << (Failed ? "FAIL, " : "PASS\n"););
if (Failed) {
if (ScopeStack.empty()) {
LLVM_DEBUG(dbgs() << "returning Fail\n");
return MCDisassembler::Fail;
}
Ptr = ScopeStack.pop_back_val();
LLVM_DEBUG(dbgs() << "continuing at " << Ptr - DecodeTable << '\n');
}
break;
})";
if (HasCheckPredicate) {
OS << R"(
case MCD::OPC_CheckPredicate: {
// Decode the Predicate Index value.
unsigned PIdx = decodeULEB128AndIncUnsafe(Ptr);
// Check the predicate.
bool Failed = !checkDecoderPredicate(PIdx, Bits);
LLVM_DEBUG(dbgs() << Loc << ": OPC_CheckPredicate(" << PIdx << "): "
<< (Failed ? "FAIL, " : "PASS\n"););
if (Failed) {
if (ScopeStack.empty()) {
LLVM_DEBUG(dbgs() << "returning Fail\n");
return MCDisassembler::Fail;
}
Ptr = ScopeStack.pop_back_val();
LLVM_DEBUG(dbgs() << "continuing at " << Ptr - DecodeTable << '\n');
}
break;
})";
}
OS << R"(
case MCD::OPC_Decode: {
// Decode the Opcode value.
unsigned Opc = decodeULEB128AndIncUnsafe(Ptr);
unsigned DecodeIdx = decodeULEB128AndIncUnsafe(Ptr);
MI.clear();
MI.setOpcode(Opc);
bool DecodeComplete;)";
if (IsVarLenInst) {
OS << "\n unsigned Len = InstrLenTable[Opc];\n"
<< " makeUp(insn, Len);";
}
OS << R"(
S = decodeToMCInst(DecodeIdx, S, insn, MI, Address, DisAsm, DecodeComplete);
assert(DecodeComplete);
LLVM_DEBUG(dbgs() << Loc << ": OPC_Decode: opcode " << Opc
<< ", using decoder " << DecodeIdx << ": "
<< (S != MCDisassembler::Fail ? "PASS\n" : "FAIL\n"));
return S;
})";
if (HasTryDecode) {
OS << R"(
case MCD::OPC_TryDecode: {
// Decode the Opcode value.
unsigned Opc = decodeULEB128AndIncUnsafe(Ptr);
unsigned DecodeIdx = decodeULEB128AndIncUnsafe(Ptr);
// Perform the decode operation.
MCInst TmpMI;
TmpMI.setOpcode(Opc);
bool DecodeComplete;
S = decodeToMCInst(DecodeIdx, S, insn, TmpMI, Address, DisAsm, DecodeComplete);
LLVM_DEBUG(dbgs() << Loc << ": OPC_TryDecode: opcode " << Opc
<< ", using decoder " << DecodeIdx << ": ");
if (DecodeComplete) {
// Decoding complete.
LLVM_DEBUG(dbgs() << (S != MCDisassembler::Fail ? "PASS\n" : "FAIL\n"));
MI = TmpMI;
return S;
}
assert(S == MCDisassembler::Fail);
if (ScopeStack.empty()) {
LLVM_DEBUG(dbgs() << "FAIL, returning FAIL\n");
return MCDisassembler::Fail;
}
Ptr = ScopeStack.pop_back_val();
LLVM_DEBUG(dbgs() << "FAIL, continuing at " << Ptr - DecodeTable << '\n');
// Reset decode status. This also drops a SoftFail status that could be
// set before the decode attempt.
S = MCDisassembler::Success;
break;
})";
}
if (HasSoftFail) {
OS << R"(
case MCD::OPC_SoftFail: {
// Decode the mask values.
uint64_t PositiveMask = decodeULEB128AndIncUnsafe(Ptr);
uint64_t NegativeMask = decodeULEB128AndIncUnsafe(Ptr);
bool Failed = (insn & PositiveMask) != 0 || (~insn & NegativeMask) != 0;
if (Failed)
S = MCDisassembler::SoftFail;
LLVM_DEBUG(dbgs() << Loc << ": OPC_SoftFail: " << (Failed ? "FAIL\n" : "PASS\n"));
break;
})";
}
OS << R"(
}
}
llvm_unreachable("bogosity detected in disassembler state machine!");
}
)";
}
/// Collects all HwModes referenced by the target for encoding purposes.
void DecoderEmitter::collectHwModesReferencedForEncodings(
std::vector<unsigned> &HwModeIDs,
NamespacesHwModesMap &NamespacesWithHwModes) const {
SmallBitVector BV(CGH.getNumModeIds());
for (const auto &MS : CGH.getHwModeSelects()) {
for (auto [HwModeID, EncodingDef] : MS.second.Items) {
if (EncodingDef->isSubClassOf("InstructionEncoding")) {
StringRef DecoderNamespace =
EncodingDef->getValueAsString("DecoderNamespace");
NamespacesWithHwModes[DecoderNamespace].insert(HwModeID);
BV.set(HwModeID);
}
}
}
// FIXME: Can't do `HwModeIDs.assign(BV.set_bits_begin(), BV.set_bits_end())`
// because const_set_bits_iterator_impl is not copy-assignable.
// This breaks some MacOS builds.
llvm::copy(BV.set_bits(), std::back_inserter(HwModeIDs));
}
void DecoderEmitter::handleHwModesUnrelatedEncodings(
unsigned EncodingID, ArrayRef<unsigned> HwModeIDs,
NamespacesHwModesMap &NamespacesWithHwModes) {
switch (DecoderEmitterSuppressDuplicates) {
case SUPPRESSION_DISABLE: {
for (unsigned HwModeID : HwModeIDs)
EncodingIDsByHwMode[HwModeID].push_back(EncodingID);
break;
}
case SUPPRESSION_LEVEL1: {
StringRef DecoderNamespace = Encodings[EncodingID].getDecoderNamespace();
auto It = NamespacesWithHwModes.find(DecoderNamespace);
if (It != NamespacesWithHwModes.end()) {
for (unsigned HwModeID : It->second)
EncodingIDsByHwMode[HwModeID].push_back(EncodingID);
} else {
// Only emit the encoding once, as it's DecoderNamespace doesn't
// contain any HwModes.
EncodingIDsByHwMode[DefaultMode].push_back(EncodingID);
}
break;
}
case SUPPRESSION_LEVEL2:
EncodingIDsByHwMode[DefaultMode].push_back(EncodingID);
break;
}
}
/// Checks if the given target-specific non-pseudo instruction
/// is a candidate for decoding.
static bool isDecodableInstruction(const Record *InstDef) {
return !InstDef->getValueAsBit("isAsmParserOnly") &&
!InstDef->getValueAsBit("isCodeGenOnly");
}
/// Checks if the given encoding is valid.
static bool isValidEncoding(const Record *EncodingDef) {
const RecordVal *InstField = EncodingDef->getValue("Inst");
if (!InstField)
return false;
if (const auto *InstInit = dyn_cast<BitsInit>(InstField->getValue())) {
// Fixed-length encoding. Size must be non-zero.
if (!EncodingDef->getValueAsInt("Size"))
return false;
// At least one of the encoding bits must be complete (not '?').
// FIXME: This should take SoftFail field into account.
return !InstInit->allInComplete();
}
if (const auto *InstInit = dyn_cast<DagInit>(InstField->getValue())) {
// Variable-length encoding.
// At least one of the encoding bits must be complete (not '?').
VarLenInst VLI(InstInit, InstField);
return !all_of(VLI, [](const EncodingSegment &Segment) {
return isa<UnsetInit>(Segment.Value);
});
}
// Inst field is neither BitsInit nor DagInit. This is something unsupported.
return false;
}
/// Parses all InstructionEncoding instances and fills internal data structures.
void DecoderEmitter::parseInstructionEncodings() {
// First, collect all encoding-related HwModes referenced by the target.
// And establish a mapping table between DecoderNamespace and HwMode.
// If HwModeNames is empty, add the default mode so we always have one HwMode.
std::vector<unsigned> HwModeIDs;
NamespacesHwModesMap NamespacesWithHwModes;
collectHwModesReferencedForEncodings(HwModeIDs, NamespacesWithHwModes);
if (HwModeIDs.empty())
HwModeIDs.push_back(DefaultMode);
ArrayRef<const CodeGenInstruction *> Instructions =
Target.getTargetNonPseudoInstructions();
Encodings.reserve(Instructions.size());
for (const CodeGenInstruction *Inst : Instructions) {
const Record *InstDef = Inst->TheDef;
if (!isDecodableInstruction(InstDef)) {
++NumEncodingsLackingDisasm;
continue;
}
if (const Record *RV = InstDef->getValueAsOptionalDef("EncodingInfos")) {
EncodingInfoByHwMode EBM(RV, CGH);
for (auto [HwModeID, EncodingDef] : EBM) {
if (!isValidEncoding(EncodingDef)) {
// TODO: Should probably give a warning.
++NumEncodingsOmitted;
continue;
}
unsigned EncodingID = Encodings.size();
Encodings.emplace_back(EncodingDef, Inst);
EncodingIDsByHwMode[HwModeID].push_back(EncodingID);
}
continue; // Ignore encoding specified by Instruction itself.
}
if (!isValidEncoding(InstDef)) {
++NumEncodingsOmitted;
continue;
}
unsigned EncodingID = Encodings.size();
Encodings.emplace_back(InstDef, Inst);
// This instruction is encoded the same on all HwModes.
// According to user needs, add it to all, some, or only the default HwMode.
handleHwModesUnrelatedEncodings(EncodingID, HwModeIDs,
NamespacesWithHwModes);
}
for (const Record *EncodingDef :
RK.getAllDerivedDefinitions("AdditionalEncoding")) {
const Record *InstDef = EncodingDef->getValueAsDef("AliasOf");
// TODO: Should probably give a warning in these cases.
// What's the point of specifying an additional encoding
// if it is invalid or if the instruction is not decodable?
if (!isDecodableInstruction(InstDef)) {
++NumEncodingsLackingDisasm;
continue;
}
if (!isValidEncoding(EncodingDef)) {
++NumEncodingsOmitted;
continue;
}
unsigned EncodingID = Encodings.size();
Encodings.emplace_back(EncodingDef, &Target.getInstruction(InstDef));
EncodingIDsByHwMode[DefaultMode].push_back(EncodingID);
}
// Do some statistics.
NumInstructions = Instructions.size();
NumEncodingsSupported = Encodings.size();
NumEncodings = NumEncodingsSupported + NumEncodingsOmitted;
}
DecoderEmitter::DecoderEmitter(const RecordKeeper &RK)
: RK(RK), Target(RK), CGH(Target.getHwModes()) {
Target.reverseBitsForLittleEndianEncoding();
parseInstructionEncodings();
}
// Emits disassembler code for instruction decoding.
void DecoderEmitter::run(raw_ostream &o) const {
formatted_raw_ostream OS(o);
OS << R"(
#include "llvm/MC/MCInst.h"
#include "llvm/MC/MCSubtargetInfo.h"
#include "llvm/Support/DataTypes.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/LEB128.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/TargetParser/SubtargetFeature.h"
#include <assert.h>
namespace {
// InsnBitWidth is essentially a type trait used by the decoder emitter to query
// the supported bitwidth for a given type. But default, the value is 0, making
// it an invalid type for use as `InsnType` when instantiating the decoder.
// Individual targets are expected to provide specializations for these based
// on their usage.
template <typename T> constexpr uint32_t InsnBitWidth = 0;
)";
// Do extra bookkeeping for variable-length encodings.
bool IsVarLenInst = Target.hasVariableLengthEncodings();
unsigned MaxInstLen = 0;
if (IsVarLenInst) {
std::vector<unsigned> InstrLen(Target.getInstructions().size(), 0);
for (const InstructionEncoding &Encoding : Encodings) {
MaxInstLen = std::max(MaxInstLen, Encoding.getBitWidth());
InstrLen[Target.getInstrIntValue(Encoding.getInstruction()->TheDef)] =
Encoding.getBitWidth();
}
// For variable instruction, we emit an instruction length table to let the
// decoder know how long the instructions are. You can see example usage in
// M68k's disassembler.
emitInstrLenTable(OS, InstrLen);
}
// Map of (bitwidth, namespace, hwmode) tuple to encoding IDs.
// Its organized as a nested map, with the (namespace, hwmode) as the key for
// the inner map and bitwidth as the key for the outer map. We use std::map
// for deterministic iteration order so that the code emitted is also
// deterministic.
using InnerKeyTy = std::pair<StringRef, unsigned>;
using InnerMapTy = std::map<InnerKeyTy, std::vector<unsigned>>;
std::map<unsigned, InnerMapTy> EncMap;
for (const auto &[HwModeID, EncodingIDs] : EncodingIDsByHwMode) {
for (unsigned EncodingID : EncodingIDs) {
const InstructionEncoding &Encoding = Encodings[EncodingID];
const unsigned BitWidth =
IsVarLenInst ? MaxInstLen : Encoding.getBitWidth();
StringRef DecoderNamespace = Encoding.getDecoderNamespace();
EncMap[BitWidth][{DecoderNamespace, HwModeID}].push_back(EncodingID);
}
}
// Variable length instructions use the same `APInt` type for all instructions
// so we cannot specialize decoders based on instruction bitwidths (which
// requires using different `InstType` for differet bitwidths for the correct
// template specialization to kick in).
if (IsVarLenInst && SpecializeDecodersPerBitwidth)
PrintFatalError(
"Cannot specialize decoders for variable length instuctions");
// Entries in `EncMap` are already sorted by bitwidth. So bucketing per
// bitwidth can be done on-the-fly as we iterate over the map.
DecoderTableInfo TableInfo;
DecoderTableBuilder TableBuilder(Target, Encodings, TableInfo);
unsigned OpcodeMask = 0;
for (const auto &[BitWidth, BWMap] : EncMap) {
for (const auto &[Key, EncodingIDs] : BWMap) {
auto [DecoderNamespace, HwModeID] = Key;
// Emit the decoder for this (namespace, hwmode, width) combination.
FilterChooser FC(Encodings, EncodingIDs);
// The decode table is cleared for each top level decoder function. The
// predicates and decoders themselves, however, are shared across
// different decoders to give more opportunities for uniqueing.
// - If `SpecializeDecodersPerBitwidth` is enabled, decoders are shared
// across all decoder tables for a given bitwidth, else they are shared
// across all decoder tables.
// - predicates are shared across all decoder tables.
TableInfo.Table.clear();
TableBuilder.buildTable(FC, BitWidth);
// Print the table to the output stream.
OpcodeMask |= emitTable(OS, TableInfo.Table, DecoderNamespace, HwModeID,
BitWidth, EncodingIDs);
}
// Each BitWidth get's its own decoders and decoder function if
// SpecializeDecodersPerBitwidth is enabled.
if (SpecializeDecodersPerBitwidth) {
emitDecoderFunction(OS, TableInfo.Decoders, BitWidth);
TableInfo.Decoders.clear();
}
}
// Emit the decoder function for the last bucket. This will also emit the
// single decoder function if SpecializeDecodersPerBitwidth = false.
if (!SpecializeDecodersPerBitwidth)
emitDecoderFunction(OS, TableInfo.Decoders, 0);
const bool HasCheckPredicate = OpcodeMask & (1 << MCD::OPC_CheckPredicate);
// Emit the predicate function.
if (HasCheckPredicate)
emitPredicateFunction(OS, TableInfo.Predicates);
// Emit the main entry point for the decoder, decodeInstruction().
emitDecodeInstruction(OS, IsVarLenInst, OpcodeMask);
OS << "\n} // namespace\n";
}
void llvm::EmitDecoder(const RecordKeeper &RK, raw_ostream &OS) {
DecoderEmitter(RK).run(OS);
}
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