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//===- PybindUtils.h - Utilities for interop with pybind11 ------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include "mlir-c/Support.h"
#include "llvm/ADT/Twine.h"
#include "llvm/Support/DataTypes.h"
#include <pybind11/pybind11.h>
#include <pybind11/stl.h>
namespace mlir {
namespace python {
// Sets a python error, ready to be thrown to return control back to the
// python runtime.
// Correct usage:
// throw SetPyError(PyExc_ValueError, "Foobar'd");
pybind11::error_already_set SetPyError(PyObject *excClass,
const llvm::Twine &message);
/// CRTP template for special wrapper types that are allowed to be passed in as
/// 'None' function arguments and can be resolved by some global mechanic if
/// so. Such types will raise an error if this global resolution fails, and
/// it is actually illegal for them to ever be unresolved. From a user
/// perspective, they behave like a smart ptr to the underlying type (i.e.
/// 'get' method and operator-> overloaded).
/// Derived types must provide a method, which is called when an environmental
/// resolution is required. It must raise an exception if resolution fails:
/// static ReferrentTy &resolve()
/// They must also provide a parameter description that will be used in
/// error messages about mismatched types:
/// static constexpr const char kTypeDescription[] = "<Description>";
template <typename DerivedTy, typename T>
class Defaulting {
using ReferrentTy = T;
/// Type casters require the type to be default constructible, but using
/// such an instance is illegal.
Defaulting() = default;
Defaulting(ReferrentTy &referrent) : referrent(&referrent) {}
ReferrentTy *get() const { return referrent; }
ReferrentTy *operator->() { return referrent; }
ReferrentTy *referrent = nullptr;
} // namespace python
} // namespace mlir
namespace pybind11 {
namespace detail {
template <typename DefaultingTy>
struct MlirDefaultingCaster {
PYBIND11_TYPE_CASTER(DefaultingTy, _(DefaultingTy::kTypeDescription));
bool load(pybind11::handle src, bool) {
if (src.is_none()) {
// Note that we do want an exception to propagate from here as it will be
// the most informative.
value = DefaultingTy{DefaultingTy::resolve()};
return true;
// Unlike many casters that chain, these casters are expected to always
// succeed, so instead of doing an isinstance check followed by a cast,
// just cast in one step and handle the exception. Returning false (vs
// letting the exception propagate) causes higher level signature parsing
// code to produce nice error messages (other than "Cannot cast...").
try {
value = DefaultingTy{
pybind11::cast<typename DefaultingTy::ReferrentTy &>(src)};
return true;
} catch (std::exception &) {
return false;
static handle cast(DefaultingTy src, return_value_policy policy,
handle parent) {
return pybind11::cast(src, policy);
} // namespace detail
} // namespace pybind11
// Conversion utilities.
namespace mlir {
/// Accumulates into a python string from a method that accepts an
/// MlirStringCallback.
struct PyPrintAccumulator {
pybind11::list parts;
void *getUserData() { return this; }
MlirStringCallback getCallback() {
return [](MlirStringRef part, void *userData) {
PyPrintAccumulator *printAccum =
static_cast<PyPrintAccumulator *>(userData);
pybind11::str pyPart(,
part.length); // Decodes as UTF-8 by default.
pybind11::str join() {
pybind11::str delim("", 0);
return delim.attr("join")(parts);
/// Accumulates int a python file-like object, either writing text (default)
/// or binary.
class PyFileAccumulator {
PyFileAccumulator(const pybind11::object &fileObject, bool binary)
: pyWriteFunction(fileObject.attr("write")), binary(binary) {}
void *getUserData() { return this; }
MlirStringCallback getCallback() {
return [](MlirStringRef part, void *userData) {
pybind11::gil_scoped_acquire acquire;
PyFileAccumulator *accum = static_cast<PyFileAccumulator *>(userData);
if (accum->binary) {
// Note: Still has to copy and not avoidable with this API.
pybind11::bytes pyBytes(, part.length);
} else {
pybind11::str pyStr(,
part.length); // Decodes as UTF-8 by default.
pybind11::object pyWriteFunction;
bool binary;
/// Accumulates into a python string from a method that is expected to make
/// one (no more, no less) call to the callback (asserts internally on
/// violation).
struct PySinglePartStringAccumulator {
void *getUserData() { return this; }
MlirStringCallback getCallback() {
return [](MlirStringRef part, void *userData) {
PySinglePartStringAccumulator *accum =
static_cast<PySinglePartStringAccumulator *>(userData);
assert(!accum->invoked &&
"PySinglePartStringAccumulator called back multiple times");
accum->invoked = true;
accum->value = pybind11::str(, part.length);
pybind11::str takeValue() {
assert(invoked && "PySinglePartStringAccumulator not called back");
return std::move(value);
pybind11::str value;
bool invoked = false;
/// A CRTP base class for pseudo-containers willing to support Python-type
/// slicing access on top of indexed access. Calling ::bind on this class
/// will define `__len__` as well as `__getitem__` with integer and slice
/// arguments.
/// This is intended for pseudo-containers that can refer to arbitrary slices of
/// underlying storage indexed by a single integer. Indexing those with an
/// integer produces an instance of ElementTy. Indexing those with a slice
/// produces a new instance of Derived, which can be sliced further.
/// A derived class must provide the following:
/// - a `static const char *pyClassName ` field containing the name of the
/// Python class to bind;
/// - an instance method `intptr_t getRawNumElements()` that returns the
/// number
/// of elements in the backing container (NOT that of the slice);
/// - an instance method `ElementTy getRawElement(intptr_t)` that returns a
/// single element at the given linear index (NOT slice index);
/// - an instance method `Derived slice(intptr_t, intptr_t, intptr_t)` that
/// constructs a new instance of the derived pseudo-container with the
/// given slice parameters (to be forwarded to the Sliceable constructor).
/// The getRawNumElements() and getRawElement(intptr_t) callbacks must not
/// throw.
/// A derived class may additionally define:
/// - a `static void bindDerived(ClassTy &)` method to bind additional methods
/// the python class.
template <typename Derived, typename ElementTy>
class Sliceable {
using ClassTy = pybind11::class_<Derived>;
/// Transforms `index` into a legal value to access the underlying sequence.
/// Returns <0 on failure.
intptr_t wrapIndex(intptr_t index) {
if (index < 0)
index = length + index;
if (index < 0 || index >= length)
return -1;
return index;
/// Computes the linear index given the current slice properties.
intptr_t linearizeIndex(intptr_t index) {
intptr_t linearIndex = index * step + startIndex;
assert(linearIndex >= 0 &&
linearIndex < static_cast<Derived *>(this)->getRawNumElements() &&
"linear index out of bounds, the slice is ill-formed");
return linearIndex;
/// Returns the element at the given slice index. Supports negative indices
/// by taking elements in inverse order. Returns a nullptr object if out
/// of bounds.
pybind11::object getItem(intptr_t index) {
// Negative indices mean we count from the end.
index = wrapIndex(index);
if (index < 0) {
PyErr_SetString(PyExc_IndexError, "index out of range");
return {};
return pybind11::cast(
static_cast<Derived *>(this)->getRawElement(linearizeIndex(index)));
/// Returns a new instance of the pseudo-container restricted to the given
/// slice. Returns a nullptr object on failure.
pybind11::object getItemSlice(PyObject *slice) {
ssize_t start, stop, extraStep, sliceLength;
if (PySlice_GetIndicesEx(slice, length, &start, &stop, &extraStep,
&sliceLength) != 0) {
PyErr_SetString(PyExc_IndexError, "index out of range");
return {};
return pybind11::cast(static_cast<Derived *>(this)->slice(
startIndex + start * step, sliceLength, step * extraStep));
explicit Sliceable(intptr_t startIndex, intptr_t length, intptr_t step)
: startIndex(startIndex), length(length), step(step) {
assert(length >= 0 && "expected non-negative slice length");
/// Returns the `index`-th element in the slice, supports negative indices.
/// Throws if the index is out of bounds.
ElementTy getElement(intptr_t index) {
// Negative indices mean we count from the end.
index = wrapIndex(index);
if (index < 0) {
throw pybind11::index_error("index out of range");
return static_cast<Derived *>(this)->getRawElement(linearizeIndex(index));
/// Returns the size of slice.
intptr_t size() { return length; }
/// Returns a new vector (mapped to Python list) containing elements from two
/// slices. The new vector is necessary because slices may not be contiguous
/// or even come from the same original sequence.
std::vector<ElementTy> dunderAdd(Derived &other) {
std::vector<ElementTy> elements;
elements.reserve(length + other.length);
for (intptr_t i = 0; i < length; ++i) {
elements.push_back(static_cast<Derived *>(this)->getElement(i));
for (intptr_t i = 0; i < other.length; ++i) {
elements.push_back(static_cast<Derived *>(&other)->getElement(i));
return elements;
/// Binds the indexing and length methods in the Python class.
static void bind(pybind11::module &m) {
auto clazz = pybind11::class_<Derived>(m, Derived::pyClassName,
.def("__add__", &Sliceable::dunderAdd);
// Manually implement the sequence protocol via the C API. We do this
// because it is approx 4x faster than via pybind11, largely because that
// formulation requires a C++ exception to be thrown to detect end of
// sequence.
// Since we are in a C-context, any C++ exception that happens here
// will terminate the program. There is nothing in this implementation
// that should throw in a non-terminal way, so we forgo further
// exception marshalling.
// See:
auto heap_type = reinterpret_cast<PyHeapTypeObject *>(clazz.ptr());
assert(heap_type->ht_type.tp_flags & Py_TPFLAGS_HEAPTYPE &&
"must be heap type");
heap_type->as_sequence.sq_length = +[](PyObject *rawSelf) -> Py_ssize_t {
auto self = pybind11::cast<Derived *>(rawSelf);
return self->length;
// sq_item is called as part of the sequence protocol for iteration,
// list construction, etc.
heap_type->as_sequence.sq_item =
+[](PyObject *rawSelf, Py_ssize_t index) -> PyObject * {
auto self = pybind11::cast<Derived *>(rawSelf);
return self->getItem(index).release().ptr();
// mp_subscript is used for both slices and integer lookups.
heap_type->as_mapping.mp_subscript =
+[](PyObject *rawSelf, PyObject *rawSubscript) -> PyObject * {
auto self = pybind11::cast<Derived *>(rawSelf);
Py_ssize_t index = PyNumber_AsSsize_t(rawSubscript, PyExc_IndexError);
if (!PyErr_Occurred()) {
// Integer indexing.
return self->getItem(index).release().ptr();
// Assume slice-based indexing.
if (PySlice_Check(rawSubscript)) {
return self->getItemSlice(rawSubscript).release().ptr();
PyErr_SetString(PyExc_ValueError, "expected integer or slice");
return nullptr;
/// Hook for derived classes willing to bind more methods.
static void bindDerived(ClassTy &) {}
intptr_t startIndex;
intptr_t length;
intptr_t step;
} // namespace mlir