BytecodeImplementation.h

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//===- BytecodeImplementation.h - MLIR Bytecode Implementation --*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This header defines various interfaces and utilities necessary for dialects
// to hook into bytecode serialization.
//
//===----------------------------------------------------------------------===//
 
#ifndef MLIR_BYTECODE_BYTECODEIMPLEMENTATION_H
#define MLIR_BYTECODE_BYTECODEIMPLEMENTATION_H
 
#include "mlir/IR/Attributes.h"
#include "mlir/IR/Diagnostics.h"
#include "mlir/IR/Dialect.h"
#include "mlir/IR/DialectInterface.h"
#include "mlir/IR/OpImplementation.h"
#include "mlir/Support/LogicalResult.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/Twine.h"
 
namespace mlir {
//===--------------------------------------------------------------------===//
// Dialect Version Interface.
//===--------------------------------------------------------------------===//
 
/// This class is used to represent the version of a dialect, for the purpose
/// of polymorphic destruction.
class DialectVersion {
public:
  virtual ~DialectVersion() = default;
};
 
//===----------------------------------------------------------------------===//
// DialectBytecodeReader
//===----------------------------------------------------------------------===//
 
/// This class defines a virtual interface for reading a bytecode stream,
/// providing hooks into the bytecode reader. As such, this class should only be
/// derived and defined by the main bytecode reader, users (i.e. dialects)
/// should generally only interact with this class via the
/// BytecodeDialectInterface below.
class DialectBytecodeReader {
public:
  virtual ~DialectBytecodeReader() = default;
 
  /// Emit an error to the reader.
  virtual InFlightDiagnostic emitError(const Twine &msg = {}) const = 0;
 
  /// Retrieve the dialect version by name if available.
  virtual FailureOr<const DialectVersion *>
  getDialectVersion(StringRef dialectName) const = 0;
 
  /// Retrieve the context associated to the reader.
  virtual MLIRContext *getContext() const = 0;
 
  /// Return the bytecode version being read.
  virtual uint64_t getBytecodeVersion() const = 0;
 
  /// Read out a list of elements, invoking the provided callback for each
  /// element. The callback function may be in any of the following forms:
  ///   * LogicalResult(T &)
  ///   * FailureOr<T>()
  template <typename T, typename CallbackFn>
  LogicalResult readList(SmallVectorImpl<T> &result, CallbackFn &&callback) {
    uint64_t size;
    if (failed(readVarInt(size)))
      return failure();
    result.reserve(size);
 
    for (uint64_t i = 0; i < size; ++i) {
      // Check if the callback uses FailureOr, or populates the result by
      // reference.
      if constexpr (llvm::function_traits<std::decay_t<CallbackFn>>::num_args) {
        T element = {};
        if (failed(callback(element)))
          return failure();
        result.emplace_back(std::move(element));
      } else {
        FailureOr<T> element = callback();
        if (failed(element))
          return failure();
        result.emplace_back(std::move(*element));
      }
    }
    return success();
  }
 
  //===--------------------------------------------------------------------===//
  // IR
  //===--------------------------------------------------------------------===//
 
  /// Read a reference to the given attribute.
  virtual LogicalResult readAttribute(Attribute &result) = 0;
  /// Read an optional reference to the given attribute. Returns success even if
  /// the Attribute isn't present.
  virtual LogicalResult readOptionalAttribute(Attribute &attr) = 0;
 
  template <typename T>
  LogicalResult readAttributes(SmallVectorImpl<T> &attrs) {
    return readList(attrs, [this](T &attr) { return readAttribute(attr); });
  }
  template <typename T>
  LogicalResult readAttribute(T &result) {
    Attribute baseResult;
    if (failed(readAttribute(baseResult)))
      return failure();
    if ((result = dyn_cast<T>(baseResult)))
      return success();
    return emitError() << "expected " << llvm::getTypeName<T>()
                       << ", but got: " << baseResult;
  }
  template <typename T>
  LogicalResult readOptionalAttribute(T &result) {
    Attribute baseResult;
    if (failed(readOptionalAttribute(baseResult)))
      return failure();
    if (!baseResult)
      return success();
    if ((result = dyn_cast<T>(baseResult)))
      return success();
    return emitError() << "expected " << llvm::getTypeName<T>()
                       << ", but got: " << baseResult;
  }
 
  /// Read a reference to the given type.
  virtual LogicalResult readType(Type &result) = 0;
  template <typename T>
  LogicalResult readTypes(SmallVectorImpl<T> &types) {
    return readList(types, [this](T &type) { return readType(type); });
  }
  template <typename T>
  LogicalResult readType(T &result) {
    Type baseResult;
    if (failed(readType(baseResult)))
      return failure();
    if ((result = dyn_cast<T>(baseResult)))
      return success();
    return emitError() << "expected " << llvm::getTypeName<T>()
                       << ", but got: " << baseResult;
  }
 
  /// Read a handle to a dialect resource.
  template <typename ResourceT>
  FailureOr<ResourceT> readResourceHandle() {
    FailureOr<AsmDialectResourceHandle> handle = readResourceHandle();
    if (failed(handle))
      return failure();
    if (auto *result = dyn_cast<ResourceT>(&*handle))
      return std::move(*result);
    return emitError() << "provided resource handle differs from the "
                          "expected resource type";
  }
 
  //===--------------------------------------------------------------------===//
  // Primitives
  //===--------------------------------------------------------------------===//
 
  /// Read a variable width integer.
  virtual LogicalResult readVarInt(uint64_t &result) = 0;
 
  /// Read a signed variable width integer.
  virtual LogicalResult readSignedVarInt(int64_t &result) = 0;
  LogicalResult readSignedVarInts(SmallVectorImpl<int64_t> &result) {
    return readList(result,
                    [this](int64_t &value) { return readSignedVarInt(value); });
  }
 
  /// Parse a variable length encoded integer whose low bit is used to encode an
  /// unrelated flag, i.e: `(integerValue << 1) | (flag ? 1 : 0)`.
  LogicalResult readVarIntWithFlag(uint64_t &result, bool &flag) {
    if (failed(readVarInt(result)))
      return failure();
    flag = result & 1;
    result >>= 1;
    return success();
  }
 
  /// Read a "small" sparse array of integer <= 32 bits elements, where
  /// index/value pairs can be compressed when the array is small.
  /// Note that only some position of the array will be read and the ones
  /// not stored in the bytecode are gonne be left untouched.
  /// If the provided array is too small for the stored indices, an error
  /// will be returned.
  template <typename T>
  LogicalResult readSparseArray(MutableArrayRef<T> array) {
    static_assert(sizeof(T) < sizeof(uint64_t), "expect integer < 64 bits");
    static_assert(std::is_integral<T>::value, "expects integer");
    uint64_t nonZeroesCount;
    bool useSparseEncoding;
    if (failed(readVarIntWithFlag(nonZeroesCount, useSparseEncoding)))
      return failure();
    if (nonZeroesCount == 0)
      return success();
    if (!useSparseEncoding) {
      // This is a simple dense array.
      if (nonZeroesCount > array.size()) {
        emitError("trying to read an array of ")
            << nonZeroesCount << " but only " << array.size()
            << " storage available.";
        return failure();
      }
      for (int64_t index : llvm::seq<int64_t>(0, nonZeroesCount)) {
        uint64_t value;
        if (failed(readVarInt(value)))
          return failure();
        array[index] = value;
      }
      return success();
    }
    // Read sparse encoding
    // This is the number of bits used for packing the index with the value.
    uint64_t indexBitSize;
    if (failed(readVarInt(indexBitSize)))
      return failure();
    constexpr uint64_t maxIndexBitSize = 8;
    if (indexBitSize > maxIndexBitSize) {
      emitError("reading sparse array with indexing above 8 bits: ")
          << indexBitSize;
      return failure();
    }
    for (uint32_t count : llvm::seq<uint32_t>(0, nonZeroesCount)) {
      (void)count;
      uint64_t indexValuePair;
      if (failed(readVarInt(indexValuePair)))
        return failure();
      uint64_t index = indexValuePair & ~(uint64_t(-1) << (indexBitSize));
      uint64_t value = indexValuePair >> indexBitSize;
      if (index >= array.size()) {
        emitError("reading a sparse array found index ")
            << index << " but only " << array.size() << " storage available.";
        return failure();
      }
      array[index] = value;
    }
    return success();
  }
 
  /// Read an APInt that is known to have been encoded with the given width.
  virtual FailureOr<APInt> readAPIntWithKnownWidth(unsigned bitWidth) = 0;
 
  /// Read an APFloat that is known to have been encoded with the given
  /// semantics.
  virtual FailureOr<APFloat>
  readAPFloatWithKnownSemantics(const llvm::fltSemantics &semantics) = 0;
 
  /// Read a string from the bytecode.
  virtual LogicalResult readString(StringRef &result) = 0;
 
  /// Read a blob from the bytecode.
  virtual LogicalResult readBlob(ArrayRef<char> &result) = 0;
 
  /// Read a bool from the bytecode.
  virtual LogicalResult readBool(bool &result) = 0;
 
private:
  /// Read a handle to a dialect resource.
  virtual FailureOr<AsmDialectResourceHandle> readResourceHandle() = 0;
};
 
//===----------------------------------------------------------------------===//
// DialectBytecodeWriter
//===----------------------------------------------------------------------===//
 
/// This class defines a virtual interface for writing to a bytecode stream,
/// providing hooks into the bytecode writer. As such, this class should only be
/// derived and defined by the main bytecode writer, users (i.e. dialects)
/// should generally only interact with this class via the
/// BytecodeDialectInterface below.
class DialectBytecodeWriter {
public:
  virtual ~DialectBytecodeWriter() = default;
 
  //===--------------------------------------------------------------------===//
  // IR
  //===--------------------------------------------------------------------===//
 
  /// Write out a list of elements, invoking the provided callback for each
  /// element.
  template <typename RangeT, typename CallbackFn>
  void writeList(RangeT &&range, CallbackFn &&callback) {
    writeVarInt(llvm::size(range));
    for (auto &element : range)
      callback(element);
  }
 
  /// Write a reference to the given attribute.
  virtual void writeAttribute(Attribute attr) = 0;
  virtual void writeOptionalAttribute(Attribute attr) = 0;
  template <typename T>
  void writeAttributes(ArrayRef<T> attrs) {
    writeList(attrs, [this](T attr) { writeAttribute(attr); });
  }
 
  /// Write a reference to the given type.
  virtual void writeType(Type type) = 0;
  template <typename T>
  void writeTypes(ArrayRef<T> types) {
    writeList(types, [this](T type) { writeType(type); });
  }
 
  /// Write the given handle to a dialect resource.
  virtual void
  writeResourceHandle(const AsmDialectResourceHandle &resource) = 0;
 
  //===--------------------------------------------------------------------===//
  // Primitives
  //===--------------------------------------------------------------------===//
 
  /// Write a variable width integer to the output stream. This should be the
  /// preferred method for emitting integers whenever possible.
  virtual void writeVarInt(uint64_t value) = 0;
 
  /// Write a signed variable width integer to the output stream. This should be
  /// the preferred method for emitting signed integers whenever possible.
  virtual void writeSignedVarInt(int64_t value) = 0;
  void writeSignedVarInts(ArrayRef<int64_t> value) {
    writeList(value, [this](int64_t value) { writeSignedVarInt(value); });
  }
 
  /// Write a VarInt and a flag packed together.
  void writeVarIntWithFlag(uint64_t value, bool flag) {
    writeVarInt((value << 1) | (flag ? 1 : 0));
  }
 
  /// Write out a "small" sparse array of integer <= 32 bits elements, where
  /// index/value pairs can be compressed when the array is small. This method
  /// will scan the array multiple times and should not be used for large
  /// arrays. The optional provided "zero" can be used to adjust for the
  /// expected repeated value. We assume here that the array size fits in a 32
  /// bits integer.
  template <typename T>
  void writeSparseArray(ArrayRef<T> array) {
    static_assert(sizeof(T) < sizeof(uint64_t), "expect integer < 64 bits");
    static_assert(std::is_integral<T>::value, "expects integer");
    uint32_t size = array.size();
    uint32_t nonZeroesCount = 0, lastIndex = 0;
    for (uint32_t index : llvm::seq<uint32_t>(0, size)) {
      if (!array[index])
        continue;
      nonZeroesCount++;
      lastIndex = index;
    }
    // If the last position is too large, or the array isn't at least 50%
    // sparse, emit it with a dense encoding.
    if (lastIndex > 256 || nonZeroesCount > size / 2) {
      // Emit the array size and a flag which indicates whether it is sparse.
      writeVarIntWithFlag(size, false);
      for (const T &elt : array)
        writeVarInt(elt);
      return;
    }
    // Emit sparse: first the number of elements we'll write and a flag
    // indicating it is a sparse encoding.
    writeVarIntWithFlag(nonZeroesCount, true);
    if (nonZeroesCount == 0)
      return;
    // This is the number of bits used for packing the index with the value.
    int indexBitSize = llvm::Log2_32_Ceil(lastIndex + 1);
    writeVarInt(indexBitSize);
    for (uint32_t index : llvm::seq<uint32_t>(0, lastIndex + 1)) {
      T value = array[index];
      if (!value)
        continue;
      uint64_t indexValuePair = (value << indexBitSize) | (index);
      writeVarInt(indexValuePair);
    }
  }
 
  /// Write an APInt to the bytecode stream whose bitwidth will be known
  /// externally at read time. This method is useful for encoding APInt values
  /// when the width is known via external means, such as via a type. This
  /// method should generally only be invoked if you need an APInt, otherwise
  /// use the varint methods above. APInt values are generally encoded using
  /// zigzag encoding, to enable more efficient encodings for negative values.
  virtual void writeAPIntWithKnownWidth(const APInt &value) = 0;
 
  /// Write an APFloat to the bytecode stream whose semantics will be known
  /// externally at read time. This method is useful for encoding APFloat values
  /// when the semantics are known via external means, such as via a type.
  virtual void writeAPFloatWithKnownSemantics(const APFloat &value) = 0;
 
  /// Write a string to the bytecode, which is owned by the caller and is
  /// guaranteed to not die before the end of the bytecode process. This should
  /// only be called if such a guarantee can be made, such as when the string is
  /// owned by an attribute or type.
  virtual void writeOwnedString(StringRef str) = 0;
 
  /// Write a blob to the bytecode, which is owned by the caller and is
  /// guaranteed to not die before the end of the bytecode process. The blob is
  /// written as-is, with no additional compression or compaction.
  virtual void writeOwnedBlob(ArrayRef<char> blob) = 0;
 
  /// Write a bool to the output stream.
  virtual void writeOwnedBool(bool value) = 0;
 
  /// Return the bytecode version being emitted for.
  virtual int64_t getBytecodeVersion() const = 0;
};
 
//===----------------------------------------------------------------------===//
// BytecodeDialectInterface
//===----------------------------------------------------------------------===//
 
class BytecodeDialectInterface
    : public DialectInterface::Base<BytecodeDialectInterface> {
public:
  using Base::Base;
 
  //===--------------------------------------------------------------------===//
  // Reading
  //===--------------------------------------------------------------------===//
 
  /// Read an attribute belonging to this dialect from the given reader. This
  /// method should return null in the case of failure. Optionally, the dialect
  /// version can be accessed through the reader.
  virtual Attribute readAttribute(DialectBytecodeReader &reader) const {
    reader.emitError() << "dialect " << getDialect()->getNamespace()
                       << " does not support reading attributes from bytecode";
    return Attribute();
  }
 
  /// Read a type belonging to this dialect from the given reader. This method
  /// should return null in the case of failure. Optionally, the dialect version
  /// can be accessed thorugh the reader.
  virtual Type readType(DialectBytecodeReader &reader) const {
    reader.emitError() << "dialect " << getDialect()->getNamespace()
                       << " does not support reading types from bytecode";
    return Type();
  }
 
  //===--------------------------------------------------------------------===//
  // Writing
  //===--------------------------------------------------------------------===//
 
  /// Write the given attribute, which belongs to this dialect, to the given
  /// writer. This method may return failure to indicate that the given
  /// attribute could not be encoded, in which case the textual format will be
  /// used to encode this attribute instead.
  virtual LogicalResult writeAttribute(Attribute attr,
                                       DialectBytecodeWriter &writer) const {
    return failure();
  }
 
  /// Write the given type, which belongs to this dialect, to the given writer.
  /// This method may return failure to indicate that the given type could not
  /// be encoded, in which case the textual format will be used to encode this
  /// type instead.
  virtual LogicalResult writeType(Type type,
                                  DialectBytecodeWriter &writer) const {
    return failure();
  }
 
  /// Write the version of this dialect to the given writer.
  virtual void writeVersion(DialectBytecodeWriter &writer) const {}
 
  // Read the version of this dialect from the provided reader and return it as
  // a `unique_ptr` to a dialect version object.
  virtual std::unique_ptr<DialectVersion>
  readVersion(DialectBytecodeReader &reader) const {
    reader.emitError("Dialect does not support versioning");
    return nullptr;
  }
 
  /// Hook invoked after parsing completed, if a version directive was present
  /// and included an entry for the current dialect. This hook offers the
  /// opportunity to the dialect to visit the IR and upgrades constructs emitted
  /// by the version of the dialect corresponding to the provided version.
  virtual LogicalResult
  upgradeFromVersion(Operation *topLevelOp,
                     const DialectVersion &version) const {
    return success();
  }
};
 
/// Helper for resource handle reading that returns LogicalResult.
template <typename T, typename... Ts>
static LogicalResult readResourceHandle(DialectBytecodeReader &reader,
                                        FailureOr<T> &value, Ts &&...params) {
  FailureOr<T> handle = reader.readResourceHandle<T>();
  if (failed(handle))
    return failure();
  if (auto *result = dyn_cast<T>(&*handle)) {
    value = std::move(*result);
    return success();
  }
  return failure();
}
 
/// Helper method that injects context only if needed, this helps unify some of
/// the attribute construction methods.
template <typename T, typename... Ts>
auto get(MLIRContext *context, Ts &&...params) {
  // Prefer a direct `get` method if one exists.
  if constexpr (llvm::is_detected<detail::has_get_method, T, Ts...>::value) {
    (void)context;
    return T::get(std::forward<Ts>(params)...);
  } else if constexpr (llvm::is_detected<detail::has_get_method, T,
                                         MLIRContext *, Ts...>::value) {
    return T::get(context, std::forward<Ts>(params)...);
  } else {
    // Otherwise, pass to the base get.
    return T::Base::get(context, std::forward<Ts>(params)...);
  }
}
 
} // namespace mlir
 
#endif // MLIR_BYTECODE_BYTECODEIMPLEMENTATION_H