mlir/lib/Bindings/Python/IRModule.h

//===- IRModules.h - IR Submodules of pybind module -----------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//

#ifndef MLIR_BINDINGS_PYTHON_IRMODULES_H
#define MLIR_BINDINGS_PYTHON_IRMODULES_H

#include <vector>

#include "PybindUtils.h"

#include "mlir-c/AffineExpr.h"
#include "mlir-c/AffineMap.h"
#include "mlir-c/IR.h"
#include "mlir-c/IntegerSet.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/Optional.h"

namespace mlir {
namespace python {

class PyBlock;
class PyInsertionPoint;
class PyLocation;
class DefaultingPyLocation;
class PyMlirContext;
class DefaultingPyMlirContext;
class PyModule;
class PyOperation;
class PyType;
class PySymbolTable;
class PyValue;

/// Template for a reference to a concrete type which captures a python
/// reference to its underlying python object.
template <typename T>
class PyObjectRef {
public:
  PyObjectRef(T *referrent, pybind11::object object)
      : referrent(referrent), object(std::move(object)) {
    assert(this->referrent &&
           "cannot construct PyObjectRef with null referrent");
    assert(this->object && "cannot construct PyObjectRef with null object");
  }
  PyObjectRef(PyObjectRef &&other)
      : referrent(other.referrent), object(std::move(other.object)) {
    other.referrent = nullptr;
    assert(!other.object);
  }
  PyObjectRef(const PyObjectRef &other)
      : referrent(other.referrent), object(other.object /* copies */) {}
  ~PyObjectRef() {}

  int getRefCount() {
    if (!object)
      return 0;
    return object.ref_count();
  }

  /// Releases the object held by this instance, returning it.
  /// This is the proper thing to return from a function that wants to return
  /// the reference. Note that this does not work from initializers.
  pybind11::object releaseObject() {
    assert(referrent && object);
    referrent = nullptr;
    auto stolen = std::move(object);
    return stolen;
  }

  T *get() { return referrent; }
  T *operator->() {
    assert(referrent && object);
    return referrent;
  }
  pybind11::object getObject() {
    assert(referrent && object);
    return object;
  }
  operator bool() const { return referrent && object; }

private:
  T *referrent;
  pybind11::object object;
};

/// Tracks an entry in the thread context stack. New entries are pushed onto
/// here for each with block that activates a new InsertionPoint, Context or
/// Location.
///
/// Pushing either a Location or InsertionPoint also pushes its associated
/// Context. Pushing a Context will not modify the Location or InsertionPoint
/// unless if they are from a different context, in which case, they are
/// cleared.
class PyThreadContextEntry {
public:
  enum class FrameKind {
    Context,
    InsertionPoint,
    Location,
  };

  PyThreadContextEntry(FrameKind frameKind, pybind11::object context,
                       pybind11::object insertionPoint,
                       pybind11::object location)
      : context(std::move(context)), insertionPoint(std::move(insertionPoint)),
        location(std::move(location)), frameKind(frameKind) {}

  /// Gets the top of stack context and return nullptr if not defined.
  static PyMlirContext *getDefaultContext();

  /// Gets the top of stack insertion point and return nullptr if not defined.
  static PyInsertionPoint *getDefaultInsertionPoint();

  /// Gets the top of stack location and returns nullptr if not defined.
  static PyLocation *getDefaultLocation();

  PyMlirContext *getContext();
  PyInsertionPoint *getInsertionPoint();
  PyLocation *getLocation();
  FrameKind getFrameKind() { return frameKind; }

  /// Stack management.
  static PyThreadContextEntry *getTopOfStack();
  static pybind11::object pushContext(PyMlirContext &context);
  static void popContext(PyMlirContext &context);
  static pybind11::object pushInsertionPoint(PyInsertionPoint &insertionPoint);
  static void popInsertionPoint(PyInsertionPoint &insertionPoint);
  static pybind11::object pushLocation(PyLocation &location);
  static void popLocation(PyLocation &location);

  /// Gets the thread local stack.
  static std::vector<PyThreadContextEntry> &getStack();

private:
  static void push(FrameKind frameKind, pybind11::object context,
                   pybind11::object insertionPoint, pybind11::object location);

  /// An object reference to the PyContext.
  pybind11::object context;
  /// An object reference to the current insertion point.
  pybind11::object insertionPoint;
  /// An object reference to the current location.
  pybind11::object location;
  // The kind of push that was performed.
  FrameKind frameKind;
};

/// Wrapper around MlirContext.
using PyMlirContextRef = PyObjectRef<PyMlirContext>;
class PyMlirContext {
public:
  PyMlirContext() = delete;
  PyMlirContext(const PyMlirContext &) = delete;
  PyMlirContext(PyMlirContext &&) = delete;

  /// For the case of a python __init__ (py::init) method, pybind11 is quite
  /// strict about needing to return a pointer that is not yet associated to
  /// an py::object. Since the forContext() method acts like a pool, possibly
  /// returning a recycled context, it does not satisfy this need. The usual
  /// way in python to accomplish such a thing is to override __new__, but
  /// that is also not supported by pybind11. Instead, we use this entry
  /// point which always constructs a fresh context (which cannot alias an
  /// existing one because it is fresh).
  static PyMlirContext *createNewContextForInit();

  /// Returns a context reference for the singleton PyMlirContext wrapper for
  /// the given context.
  static PyMlirContextRef forContext(MlirContext context);
  ~PyMlirContext();

  /// Accesses the underlying MlirContext.
  MlirContext get() { return context; }

  /// Gets a strong reference to this context, which will ensure it is kept
  /// alive for the life of the reference.
  PyMlirContextRef getRef() {
    return PyMlirContextRef(this, pybind11::cast(this));
  }

  /// Gets a capsule wrapping the void* within the MlirContext.
  pybind11::object getCapsule();

  /// Creates a PyMlirContext from the MlirContext wrapped by a capsule.
  /// Note that PyMlirContext instances are uniqued, so the returned object
  /// may be a pre-existing object. Ownership of the underlying MlirContext
  /// is taken by calling this function.
  static pybind11::object createFromCapsule(pybind11::object capsule);

  /// Gets the count of live context objects. Used for testing.
  static size_t getLiveCount();

  /// Gets the count of live operations associated with this context.
  /// Used for testing.
  size_t getLiveOperationCount();

  /// Gets the count of live modules associated with this context.
  /// Used for testing.
  size_t getLiveModuleCount();

  /// Enter and exit the context manager.
  pybind11::object contextEnter();
  void contextExit(pybind11::object excType, pybind11::object excVal,
                   pybind11::object excTb);

private:
  PyMlirContext(MlirContext context);
  // Interns the mapping of live MlirContext::ptr to PyMlirContext instances,
  // preserving the relationship that an MlirContext maps to a single
  // PyMlirContext wrapper. This could be replaced in the future with an
  // extension mechanism on the MlirContext for stashing user pointers.
  // Note that this holds a handle, which does not imply ownership.
  // Mappings will be removed when the context is destructed.
  using LiveContextMap = llvm::DenseMap<void *, PyMlirContext *>;
  static LiveContextMap &getLiveContexts();

  // Interns all live modules associated with this context. Modules tracked
  // in this map are valid. When a module is invalidated, it is removed
  // from this map, and while it still exists as an instance, any
  // attempt to access it will raise an error.
  using LiveModuleMap =
      llvm::DenseMap<const void *, std::pair<pybind11::handle, PyModule *>>;
  LiveModuleMap liveModules;

  // Interns all live operations associated with this context. Operations
  // tracked in this map are valid. When an operation is invalidated, it is
  // removed from this map, and while it still exists as an instance, any
  // attempt to access it will raise an error.
  using LiveOperationMap =
      llvm::DenseMap<void *, std::pair<pybind11::handle, PyOperation *>>;
  LiveOperationMap liveOperations;

  MlirContext context;
  friend class PyModule;
  friend class PyOperation;
};

/// Used in function arguments when None should resolve to the current context
/// manager set instance.
class DefaultingPyMlirContext
    : public Defaulting<DefaultingPyMlirContext, PyMlirContext> {
public:
  using Defaulting::Defaulting;
  static constexpr const char kTypeDescription[] = "mlir.ir.Context";
  static PyMlirContext &resolve();
};

/// Base class for all objects that directly or indirectly depend on an
/// MlirContext. The lifetime of the context will extend at least to the
/// lifetime of these instances.
/// Immutable objects that depend on a context extend this directly.
class BaseContextObject {
public:
  BaseContextObject(PyMlirContextRef ref) : contextRef(std::move(ref)) {
    assert(this->contextRef &&
           "context object constructed with null context ref");
  }

  /// Accesses the context reference.
  PyMlirContextRef &getContext() { return contextRef; }

private:
  PyMlirContextRef contextRef;
};

/// Wrapper around an MlirDialect. This is exported as `DialectDescriptor` in
/// order to differentiate it from the `Dialect` base class which is extended by
/// plugins which extend dialect functionality through extension python code.
/// This should be seen as the "low-level" object and `Dialect` as the
/// high-level, user facing object.
class PyDialectDescriptor : public BaseContextObject {
public:
  PyDialectDescriptor(PyMlirContextRef contextRef, MlirDialect dialect)
      : BaseContextObject(std::move(contextRef)), dialect(dialect) {}

  MlirDialect get() { return dialect; }

private:
  MlirDialect dialect;
};

/// User-level object for accessing dialects with dotted syntax such as:
///   ctx.dialect.std
class PyDialects : public BaseContextObject {
public:
  PyDialects(PyMlirContextRef contextRef)
      : BaseContextObject(std::move(contextRef)) {}

  MlirDialect getDialectForKey(const std::string &key, bool attrError);
};

/// User-level dialect object. For dialects that have a registered extension,
/// this will be the base class of the extension dialect type. For un-extended,
/// objects of this type will be returned directly.
class PyDialect {
public:
  PyDialect(pybind11::object descriptor) : descriptor(std::move(descriptor)) {}

  pybind11::object getDescriptor() { return descriptor; }

private:
  pybind11::object descriptor;
};

/// Wrapper around an MlirLocation.
class PyLocation : public BaseContextObject {
public:
  PyLocation(PyMlirContextRef contextRef, MlirLocation loc)
      : BaseContextObject(std::move(contextRef)), loc(loc) {}

  operator MlirLocation() const { return loc; }
  MlirLocation get() const { return loc; }

  /// Enter and exit the context manager.
  pybind11::object contextEnter();
  void contextExit(pybind11::object excType, pybind11::object excVal,
                   pybind11::object excTb);

  /// Gets a capsule wrapping the void* within the MlirLocation.
  pybind11::object getCapsule();

  /// Creates a PyLocation from the MlirLocation wrapped by a capsule.
  /// Note that PyLocation instances are uniqued, so the returned object
  /// may be a pre-existing object. Ownership of the underlying MlirLocation
  /// is taken by calling this function.
  static PyLocation createFromCapsule(pybind11::object capsule);

private:
  MlirLocation loc;
};

/// Used in function arguments when None should resolve to the current context
/// manager set instance.
class DefaultingPyLocation
    : public Defaulting<DefaultingPyLocation, PyLocation> {
public:
  using Defaulting::Defaulting;
  static constexpr const char kTypeDescription[] = "mlir.ir.Location";
  static PyLocation &resolve();

  operator MlirLocation() const { return *get(); }
};

/// Wrapper around MlirModule.
/// This is the top-level, user-owned object that contains regions/ops/blocks.
class PyModule;
using PyModuleRef = PyObjectRef<PyModule>;
class PyModule : public BaseContextObject {
public:
  /// Returns a PyModule reference for the given MlirModule. This may return
  /// a pre-existing or new object.
  static PyModuleRef forModule(MlirModule module);
  PyModule(PyModule &) = delete;
  PyModule(PyMlirContext &&) = delete;
  ~PyModule();

  /// Gets the backing MlirModule.
  MlirModule get() { return module; }

  /// Gets a strong reference to this module.
  PyModuleRef getRef() {
    return PyModuleRef(this,
                       pybind11::reinterpret_borrow<pybind11::object>(handle));
  }

  /// Gets a capsule wrapping the void* within the MlirModule.
  /// Note that the module does not (yet) provide a corresponding factory for
  /// constructing from a capsule as that would require uniquing PyModule
  /// instances, which is not currently done.
  pybind11::object getCapsule();

  /// Creates a PyModule from the MlirModule wrapped by a capsule.
  /// Note that PyModule instances are uniqued, so the returned object
  /// may be a pre-existing object. Ownership of the underlying MlirModule
  /// is taken by calling this function.
  static pybind11::object createFromCapsule(pybind11::object capsule);

private:
  PyModule(PyMlirContextRef contextRef, MlirModule module);
  MlirModule module;
  pybind11::handle handle;
};

/// Base class for PyOperation and PyOpView which exposes the primary, user
/// visible methods for manipulating it.
class PyOperationBase {
public:
  virtual ~PyOperationBase() = default;
  /// Implements the bound 'print' method and helps with others.
  void print(pybind11::object fileObject, bool binary,
             llvm::Optional<int64_t> largeElementsLimit, bool enableDebugInfo,
             bool prettyDebugInfo, bool printGenericOpForm, bool useLocalScope,
             bool assumeVerified);
  pybind11::object getAsm(bool binary,
                          llvm::Optional<int64_t> largeElementsLimit,
                          bool enableDebugInfo, bool prettyDebugInfo,
                          bool printGenericOpForm, bool useLocalScope,
                          bool assumeVerified);

  /// Moves the operation before or after the other operation.
  void moveAfter(PyOperationBase &other);
  void moveBefore(PyOperationBase &other);

  /// Each must provide access to the raw Operation.
  virtual PyOperation &getOperation() = 0;
};

/// Wrapper around PyOperation.
/// Operations exist in either an attached (dependent) or detached (top-level)
/// state. In the detached state (as on creation), an operation is owned by
/// the creator and its lifetime extends either until its reference count
/// drops to zero or it is attached to a parent, at which point its lifetime
/// is bounded by its top-level parent reference.
class PyOperation;
using PyOperationRef = PyObjectRef<PyOperation>;
class PyOperation : public PyOperationBase, public BaseContextObject {
public:
  ~PyOperation();
  PyOperation &getOperation() override { return *this; }

  /// Returns a PyOperation for the given MlirOperation, optionally associating
  /// it with a parentKeepAlive.
  static PyOperationRef
  forOperation(PyMlirContextRef contextRef, MlirOperation operation,
               pybind11::object parentKeepAlive = pybind11::object());

  /// Creates a detached operation. The operation must not be associated with
  /// any existing live operation.
  static PyOperationRef
  createDetached(PyMlirContextRef contextRef, MlirOperation operation,
                 pybind11::object parentKeepAlive = pybind11::object());

  /// Detaches the operation from its parent block and updates its state
  /// accordingly.
  void detachFromParent() {
    mlirOperationRemoveFromParent(getOperation());
    setDetached();
    parentKeepAlive = pybind11::object();
  }

  /// Gets the backing operation.
  operator MlirOperation() const { return get(); }
  MlirOperation get() const {
    checkValid();
    return operation;
  }

  PyOperationRef getRef() {
    return PyOperationRef(
        this, pybind11::reinterpret_borrow<pybind11::object>(handle));
  }

  bool isAttached() { return attached; }
  void setAttached(pybind11::object parent = pybind11::object()) {
    assert(!attached && "operation already attached");
    attached = true;
  }
  void setDetached() {
    assert(attached && "operation already detached");
    attached = false;
  }
  void checkValid() const;

  /// Gets the owning block or raises an exception if the operation has no
  /// owning block.
  PyBlock getBlock();

  /// Gets the parent operation or raises an exception if the operation has
  /// no parent.
  llvm::Optional<PyOperationRef> getParentOperation();

  /// Gets a capsule wrapping the void* within the MlirOperation.
  pybind11::object getCapsule();

  /// Creates a PyOperation from the MlirOperation wrapped by a capsule.
  /// Ownership of the underlying MlirOperation is taken by calling this
  /// function.
  static pybind11::object createFromCapsule(pybind11::object capsule);

  /// Creates an operation. See corresponding python docstring.
  static pybind11::object
  create(std::string name, llvm::Optional<std::vector<PyType *>> results,
         llvm::Optional<std::vector<PyValue *>> operands,
         llvm::Optional<pybind11::dict> attributes,
         llvm::Optional<std::vector<PyBlock *>> successors, int regions,
         DefaultingPyLocation location, pybind11::object ip);

  /// Creates an OpView suitable for this operation.
  pybind11::object createOpView();

  /// Erases the underlying MlirOperation, removes its pointer from the
  /// parent context's live operations map, and sets the valid bit false.
  void erase();

private:
  PyOperation(PyMlirContextRef contextRef, MlirOperation operation);
  static PyOperationRef createInstance(PyMlirContextRef contextRef,
                                       MlirOperation operation,
                                       pybind11::object parentKeepAlive);

  MlirOperation operation;
  pybind11::handle handle;
  // Keeps the parent alive, regardless of whether it is an Operation or
  // Module.
  // TODO: As implemented, this facility is only sufficient for modeling the
  // trivial module parent back-reference. Generalize this to also account for
  // transitions from detached to attached and address TODOs in the
  // ir_operation.py regarding testing corresponding lifetime guarantees.
  pybind11::object parentKeepAlive;
  bool attached = true;
  bool valid = true;

  friend class PyOperationBase;
  friend class PySymbolTable;
};

/// A PyOpView is equivalent to the C++ "Op" wrappers: these are the basis for
/// providing more instance-specific accessors and serve as the base class for
/// custom ODS-style operation classes. Since this class is subclass on the
/// python side, it must present an __init__ method that operates in pure
/// python types.
class PyOpView : public PyOperationBase {
public:
  PyOpView(pybind11::object operationObject);
  PyOperation &getOperation() override { return operation; }

  static pybind11::object createRawSubclass(pybind11::object userClass);

  pybind11::object getOperationObject() { return operationObject; }

  static pybind11::object
  buildGeneric(pybind11::object cls, pybind11::list resultTypeList,
               pybind11::list operandList,
               llvm::Optional<pybind11::dict> attributes,
               llvm::Optional<std::vector<PyBlock *>> successors,
               llvm::Optional<int> regions, DefaultingPyLocation location,
               pybind11::object maybeIp);

private:
  PyOperation &operation;           // For efficient, cast-free access from C++
  pybind11::object operationObject; // Holds the reference.
};

/// Wrapper around an MlirRegion.
/// Regions are managed completely by their containing operation. Unlike the
/// C++ API, the python API does not support detached regions.
class PyRegion {
public:
  PyRegion(PyOperationRef parentOperation, MlirRegion region)
      : parentOperation(std::move(parentOperation)), region(region) {
    assert(!mlirRegionIsNull(region) && "python region cannot be null");
  }
  operator MlirRegion() const { return region; }

  MlirRegion get() { return region; }
  PyOperationRef &getParentOperation() { return parentOperation; }

  void checkValid() { return parentOperation->checkValid(); }

private:
  PyOperationRef parentOperation;
  MlirRegion region;
};

/// Wrapper around an MlirBlock.
/// Blocks are managed completely by their containing operation. Unlike the
/// C++ API, the python API does not support detached blocks.
class PyBlock {
public:
  PyBlock(PyOperationRef parentOperation, MlirBlock block)
      : parentOperation(std::move(parentOperation)), block(block) {
    assert(!mlirBlockIsNull(block) && "python block cannot be null");
  }

  MlirBlock get() { return block; }
  PyOperationRef &getParentOperation() { return parentOperation; }

  void checkValid() { return parentOperation->checkValid(); }

private:
  PyOperationRef parentOperation;
  MlirBlock block;
};

/// An insertion point maintains a pointer to a Block and a reference operation.
/// Calls to insert() will insert a new operation before the
/// reference operation. If the reference operation is null, then appends to
/// the end of the block.
class PyInsertionPoint {
public:
  /// Creates an insertion point positioned after the last operation in the
  /// block, but still inside the block.
  PyInsertionPoint(PyBlock &block);
  /// Creates an insertion point positioned before a reference operation.
  PyInsertionPoint(PyOperationBase &beforeOperationBase);

  /// Shortcut to create an insertion point at the beginning of the block.
  static PyInsertionPoint atBlockBegin(PyBlock &block);
  /// Shortcut to create an insertion point before the block terminator.
  static PyInsertionPoint atBlockTerminator(PyBlock &block);

  /// Inserts an operation.
  void insert(PyOperationBase &operationBase);

  /// Enter and exit the context manager.
  pybind11::object contextEnter();
  void contextExit(pybind11::object excType, pybind11::object excVal,
                   pybind11::object excTb);

  PyBlock &getBlock() { return block; }

private:
  // Trampoline constructor that avoids null initializing members while
  // looking up parents.
  PyInsertionPoint(PyBlock block, llvm::Optional<PyOperationRef> refOperation)
      : refOperation(std::move(refOperation)), block(std::move(block)) {}

  llvm::Optional<PyOperationRef> refOperation;
  PyBlock block;
};
/// Wrapper around the generic MlirType.
/// The lifetime of a type is bound by the PyContext that created it.
class PyType : public BaseContextObject {
public:
  PyType(PyMlirContextRef contextRef, MlirType type)
      : BaseContextObject(std::move(contextRef)), type(type) {}
  bool operator==(const PyType &other);
  operator MlirType() const { return type; }
  MlirType get() const { return type; }

  /// Gets a capsule wrapping the void* within the MlirType.
  pybind11::object getCapsule();

  /// Creates a PyType from the MlirType wrapped by a capsule.
  /// Note that PyType instances are uniqued, so the returned object
  /// may be a pre-existing object. Ownership of the underlying MlirType
  /// is taken by calling this function.
  static PyType createFromCapsule(pybind11::object capsule);

private:
  MlirType type;
};

/// CRTP base classes for Python types that subclass Type and should be
/// castable from it (i.e. via something like IntegerType(t)).
/// By default, type class hierarchies are one level deep (i.e. a
/// concrete type class extends PyType); however, intermediate python-visible
/// base classes can be modeled by specifying a BaseTy.
template <typename DerivedTy, typename BaseTy = PyType>
class PyConcreteType : public BaseTy {
public:
  // Derived classes must define statics for:
  //   IsAFunctionTy isaFunction
  //   const char *pyClassName
  using ClassTy = pybind11::class_<DerivedTy, BaseTy>;
  using IsAFunctionTy = bool (*)(MlirType);

  PyConcreteType() = default;
  PyConcreteType(PyMlirContextRef contextRef, MlirType t)
      : BaseTy(std::move(contextRef), t) {}
  PyConcreteType(PyType &orig)
      : PyConcreteType(orig.getContext(), castFrom(orig)) {}

  static MlirType castFrom(PyType &orig) {
    if (!DerivedTy::isaFunction(orig)) {
      auto origRepr = pybind11::repr(pybind11::cast(orig)).cast<std::string>();
      throw SetPyError(PyExc_ValueError, llvm::Twine("Cannot cast type to ") +
                                             DerivedTy::pyClassName +
                                             " (from " + origRepr + ")");
    }
    return orig;
  }

  static void bind(pybind11::module &m) {
    auto cls = ClassTy(m, DerivedTy::pyClassName, pybind11::module_local());
    cls.def(pybind11::init<PyType &>(), pybind11::keep_alive<0, 1>(),
            pybind11::arg("cast_from_type"));
    cls.def_static(
        "isinstance",
        [](PyType &otherType) -> bool {
          return DerivedTy::isaFunction(otherType);
        },
        pybind11::arg("other"));
    DerivedTy::bindDerived(cls);
  }

  /// Implemented by derived classes to add methods to the Python subclass.
  static void bindDerived(ClassTy &m) {}
};

/// Wrapper around the generic MlirAttribute.
/// The lifetime of a type is bound by the PyContext that created it.
class PyAttribute : public BaseContextObject {
public:
  PyAttribute(PyMlirContextRef contextRef, MlirAttribute attr)
      : BaseContextObject(std::move(contextRef)), attr(attr) {}
  bool operator==(const PyAttribute &other);
  operator MlirAttribute() const { return attr; }
  MlirAttribute get() const { return attr; }

  /// Gets a capsule wrapping the void* within the MlirAttribute.
  pybind11::object getCapsule();

  /// Creates a PyAttribute from the MlirAttribute wrapped by a capsule.
  /// Note that PyAttribute instances are uniqued, so the returned object
  /// may be a pre-existing object. Ownership of the underlying MlirAttribute
  /// is taken by calling this function.
  static PyAttribute createFromCapsule(pybind11::object capsule);

private:
  MlirAttribute attr;
};

/// Represents a Python MlirNamedAttr, carrying an optional owned name.
/// TODO: Refactor this and the C-API to be based on an Identifier owned
/// by the context so as to avoid ownership issues here.
class PyNamedAttribute {
public:
  /// Constructs a PyNamedAttr that retains an owned name. This should be
  /// used in any code that originates an MlirNamedAttribute from a python
  /// string.
  /// The lifetime of the PyNamedAttr must extend to the lifetime of the
  /// passed attribute.
  PyNamedAttribute(MlirAttribute attr, std::string ownedName);

  MlirNamedAttribute namedAttr;

private:
  // Since the MlirNamedAttr contains an internal pointer to the actual
  // memory of the owned string, it must be heap allocated to remain valid.
  // Otherwise, strings that fit within the small object optimization threshold
  // will have their memory address change as the containing object is moved,
  // resulting in an invalid aliased pointer.
  std::unique_ptr<std::string> ownedName;
};

/// CRTP base classes for Python attributes that subclass Attribute and should
/// be castable from it (i.e. via something like StringAttr(attr)).
/// By default, attribute class hierarchies are one level deep (i.e. a
/// concrete attribute class extends PyAttribute); however, intermediate
/// python-visible base classes can be modeled by specifying a BaseTy.
template <typename DerivedTy, typename BaseTy = PyAttribute>
class PyConcreteAttribute : public BaseTy {
public:
  // Derived classes must define statics for:
  //   IsAFunctionTy isaFunction
  //   const char *pyClassName
  using ClassTy = pybind11::class_<DerivedTy, BaseTy>;
  using IsAFunctionTy = bool (*)(MlirAttribute);

  PyConcreteAttribute() = default;
  PyConcreteAttribute(PyMlirContextRef contextRef, MlirAttribute attr)
      : BaseTy(std::move(contextRef), attr) {}
  PyConcreteAttribute(PyAttribute &orig)
      : PyConcreteAttribute(orig.getContext(), castFrom(orig)) {}

  static MlirAttribute castFrom(PyAttribute &orig) {
    if (!DerivedTy::isaFunction(orig)) {
      auto origRepr = pybind11::repr(pybind11::cast(orig)).cast<std::string>();
      throw SetPyError(PyExc_ValueError,
                       llvm::Twine("Cannot cast attribute to ") +
                           DerivedTy::pyClassName + " (from " + origRepr + ")");
    }
    return orig;
  }

  static void bind(pybind11::module &m) {
    auto cls = ClassTy(m, DerivedTy::pyClassName, pybind11::buffer_protocol(),
                       pybind11::module_local());
    cls.def(pybind11::init<PyAttribute &>(), pybind11::keep_alive<0, 1>(),
            pybind11::arg("cast_from_attr"));
    cls.def_static(
        "isinstance",
        [](PyAttribute &otherAttr) -> bool {
          return DerivedTy::isaFunction(otherAttr);
        },
        pybind11::arg("other"));
    cls.def_property_readonly("type", [](PyAttribute &attr) {
      return PyType(attr.getContext(), mlirAttributeGetType(attr));
    });
    DerivedTy::bindDerived(cls);
  }

  /// Implemented by derived classes to add methods to the Python subclass.
  static void bindDerived(ClassTy &m) {}
};

/// Wrapper around the generic MlirValue.
/// Values are managed completely by the operation that resulted in their
/// definition. For op result value, this is the operation that defines the
/// value. For block argument values, this is the operation that contains the
/// block to which the value is an argument (blocks cannot be detached in Python
/// bindings so such operation always exists).
class PyValue {
public:
  PyValue(PyOperationRef parentOperation, MlirValue value)
      : parentOperation(parentOperation), value(value) {}
  operator MlirValue() const { return value; }

  MlirValue get() { return value; }
  PyOperationRef &getParentOperation() { return parentOperation; }

  void checkValid() { return parentOperation->checkValid(); }

  /// Gets a capsule wrapping the void* within the MlirValue.
  pybind11::object getCapsule();

  /// Creates a PyValue from the MlirValue wrapped by a capsule. Ownership of
  /// the underlying MlirValue is still tied to the owning operation.
  static PyValue createFromCapsule(pybind11::object capsule);

private:
  PyOperationRef parentOperation;
  MlirValue value;
};

/// Wrapper around MlirAffineExpr. Affine expressions are owned by the context.
class PyAffineExpr : public BaseContextObject {
public:
  PyAffineExpr(PyMlirContextRef contextRef, MlirAffineExpr affineExpr)
      : BaseContextObject(std::move(contextRef)), affineExpr(affineExpr) {}
  bool operator==(const PyAffineExpr &other);
  operator MlirAffineExpr() const { return affineExpr; }
  MlirAffineExpr get() const { return affineExpr; }

  /// Gets a capsule wrapping the void* within the MlirAffineExpr.
  pybind11::object getCapsule();

  /// Creates a PyAffineExpr from the MlirAffineExpr wrapped by a capsule.
  /// Note that PyAffineExpr instances are uniqued, so the returned object
  /// may be a pre-existing object. Ownership of the underlying MlirAffineExpr
  /// is taken by calling this function.
  static PyAffineExpr createFromCapsule(pybind11::object capsule);

  PyAffineExpr add(const PyAffineExpr &other) const;
  PyAffineExpr mul(const PyAffineExpr &other) const;
  PyAffineExpr floorDiv(const PyAffineExpr &other) const;
  PyAffineExpr ceilDiv(const PyAffineExpr &other) const;
  PyAffineExpr mod(const PyAffineExpr &other) const;

private:
  MlirAffineExpr affineExpr;
};

class PyAffineMap : public BaseContextObject {
public:
  PyAffineMap(PyMlirContextRef contextRef, MlirAffineMap affineMap)
      : BaseContextObject(std::move(contextRef)), affineMap(affineMap) {}
  bool operator==(const PyAffineMap &other);
  operator MlirAffineMap() const { return affineMap; }
  MlirAffineMap get() const { return affineMap; }

  /// Gets a capsule wrapping the void* within the MlirAffineMap.
  pybind11::object getCapsule();

  /// Creates a PyAffineMap from the MlirAffineMap wrapped by a capsule.
  /// Note that PyAffineMap instances are uniqued, so the returned object
  /// may be a pre-existing object. Ownership of the underlying MlirAffineMap
  /// is taken by calling this function.
  static PyAffineMap createFromCapsule(pybind11::object capsule);

private:
  MlirAffineMap affineMap;
};

class PyIntegerSet : public BaseContextObject {
public:
  PyIntegerSet(PyMlirContextRef contextRef, MlirIntegerSet integerSet)
      : BaseContextObject(std::move(contextRef)), integerSet(integerSet) {}
  bool operator==(const PyIntegerSet &other);
  operator MlirIntegerSet() const { return integerSet; }
  MlirIntegerSet get() const { return integerSet; }

  /// Gets a capsule wrapping the void* within the MlirIntegerSet.
  pybind11::object getCapsule();

  /// Creates a PyIntegerSet from the MlirAffineMap wrapped by a capsule.
  /// Note that PyIntegerSet instances may be uniqued, so the returned object
  /// may be a pre-existing object. Integer sets are owned by the context.
  static PyIntegerSet createFromCapsule(pybind11::object capsule);

private:
  MlirIntegerSet integerSet;
};

/// Bindings for MLIR symbol tables.
class PySymbolTable {
public:
  /// Constructs a symbol table for the given operation.
  explicit PySymbolTable(PyOperationBase &operation);

  /// Destroys the symbol table.
  ~PySymbolTable() { mlirSymbolTableDestroy(symbolTable); }

  /// Returns the symbol (opview) with the given name, throws if there is no
  /// such symbol in the table.
  pybind11::object dunderGetItem(const std::string &name);

  /// Removes the given operation from the symbol table and erases it.
  void erase(PyOperationBase &symbol);

  /// Removes the operation with the given name from the symbol table and erases
  /// it, throws if there is no such symbol in the table.
  void dunderDel(const std::string &name);

  /// Inserts the given operation into the symbol table. The operation must have
  /// the symbol trait.
  PyAttribute insert(PyOperationBase &symbol);

  /// Gets and sets the name of a symbol op.
  static PyAttribute getSymbolName(PyOperationBase &symbol);
  static void setSymbolName(PyOperationBase &symbol, const std::string &name);

  /// Gets and sets the visibility of a symbol op.
  static PyAttribute getVisibility(PyOperationBase &symbol);
  static void setVisibility(PyOperationBase &symbol,
                            const std::string &visibility);

  /// Replaces all symbol uses within an operation. See the API
  /// mlirSymbolTableReplaceAllSymbolUses for all caveats.
  static void replaceAllSymbolUses(const std::string &oldSymbol,
                                   const std::string &newSymbol,
                                   PyOperationBase &from);

  /// Walks all symbol tables under and including 'from'.
  static void walkSymbolTables(PyOperationBase &from, bool allSymUsesVisible,
                               pybind11::object callback);

  /// Casts the bindings class into the C API structure.
  operator MlirSymbolTable() { return symbolTable; }

private:
  PyOperationRef operation;
  MlirSymbolTable symbolTable;
};

void populateIRAffine(pybind11::module &m);
void populateIRAttributes(pybind11::module &m);
void populateIRCore(pybind11::module &m);
void populateIRInterfaces(pybind11::module &m);
void populateIRTypes(pybind11::module &m);

} // namespace python
} // namespace mlir

namespace pybind11 {
namespace detail {

template <>
struct type_caster<mlir::python::DefaultingPyMlirContext>
    : MlirDefaultingCaster<mlir::python::DefaultingPyMlirContext> {};
template <>
struct type_caster<mlir::python::DefaultingPyLocation>
    : MlirDefaultingCaster<mlir::python::DefaultingPyLocation> {};

} // namespace detail
} // namespace pybind11

#endif // MLIR_BINDINGS_PYTHON_IRMODULES_H