Source code for pennylane.compiler.qjit_api
# Copyright 2023 Xanadu Quantum Technologies Inc.
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# you may not use this file except in compliance with the License.
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# http://www.apache.org/licenses/LICENSE-2.0
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"""QJIT compatible quantum and compilation operations API"""
from .compiler import (
_check_compiler_version,
CompileError,
AvailableCompilers,
available,
active_compiler,
)
[docs]def qjit(fn=None, *args, compiler="catalyst", **kwargs): # pylint:disable=keyword-arg-before-vararg
"""A decorator for just-in-time compilation of hybrid quantum programs in PennyLane.
This decorator enables both just-in-time and ahead-of-time compilation,
depending on the compiler package and whether function argument type hints
are provided.
.. note::
Currently, only two compilers are supported; the :doc:`Catalyst <catalyst:index>` hybrid
quantum-classical compiler, which works with the JAX interface, and CUDA Quantum.
For more details on Catalyst, see the :doc:`Catalyst documentation <catalyst:index>` and
:func:`catalyst.qjit`.
.. note::
Catalyst supports compiling QNodes that use ``lightning.qubit``,
``lightning.kokkos``, ``braket.local.qubit``, and ``braket.aws.qubit``
devices. It does not support ``default.qubit``.
Please see the :doc:`Catalyst documentation <catalyst:index>` for more details on
supported devices, operations, and measurements.
CUDA Quantum supports ``softwareq.qpp``, ``nvidida.custatevec``, and ``nvidia.cutensornet``.
Args:
fn (Callable): Hybrid (quantum-classical) function to compile
compiler (str): Name of the compiler to use for just-in-time compilation. Available
options include ``catalyst`` and ``cuda_quantum``.
autograph (bool): Experimental support for automatically converting Python control
flow statements to Catalyst-compatible control flow. Currently supports Python ``if``,
``elif``, ``else``, and ``for`` statements. Note that this feature requires an
available TensorFlow installation. See the
:doc:`AutoGraph guide <catalyst:dev/autograph>` for more information.
keep_intermediate (bool): Whether or not to store the intermediate files throughout the
compilation. The files are stored at the location where the Python script is called.
If ``True``, intermediate representations are available via the
:attr:`~.QJIT.mlir`, :attr:`~.QJIT.jaxpr`, and :attr:`~.QJIT.qir`, representing
different stages in the optimization process.
verbosity (bool): If ``True``, the tools and flags used by Catalyst behind the scenes are
printed out.
logfile (TextIOWrapper): File object to write verbose messages to (default is
``sys.stderr``)
pipelines (List[Tuple[str, List[str]]]): A list of pipelines to be executed. The
elements of this list are named sequences of MLIR passes to be executed. A ``None``
value (the default) results in the execution of the default pipeline. This option is
considered to be used by advanced users for low-level debugging purposes.
static_argnums(int or Seqence[Int]): an index or a sequence of indices that specifies the
positions of static arguments.
abstracted_axes (Sequence[Sequence[str]] or Dict[int, str] or Sequence[Dict[int, str]]):
An experimental option to specify dynamic tensor shapes.
This option affects the compilation of the annotated function.
Function arguments with ``abstracted_axes`` specified will be compiled to ranked tensors
with dynamic shapes. For more details, please see the Dynamically-shaped Arrays section
below.
Returns:
catalyst.QJIT: A class that, when executed, just-in-time compiles and executes the
decorated function
Raises:
FileExistsError: Unable to create temporary directory
PermissionError: Problems creating temporary directory
OSError: Problems while creating folder for intermediate files
AutoGraphError: Raised if there was an issue converting the given the function(s).
ImportError: Raised if AutoGraph is turned on and TensorFlow could not be found.
**Example**
In just-in-time (JIT) mode, the compilation is triggered at the call site the
first time the quantum function is executed. For example, ``circuit`` is
compiled as early as the first call.
.. code-block:: python
dev = qml.device("lightning.qubit", wires=2)
@qml.qjit
@qml.qnode(dev)
def circuit(theta):
qml.Hadamard(wires=0)
qml.RX(theta, wires=1)
qml.CNOT(wires=[0,1])
return qml.expval(qml.Z(1))
>>> circuit(0.5) # the first call, compilation occurs here
array(0.)
>>> circuit(0.5) # the precompiled quantum function is called
array(0.)
:func:`~.qjit` compiled programs also support nested container types as inputs and outputs of
compiled functions. This includes lists and dictionaries, as well as any data structure implementing
the `JAX PyTree <https://jax.readthedocs.io/en/latest/pytrees.html>`__.
.. code-block:: python
dev = qml.device("lightning.qubit", wires=2)
@qml.qjit
@qml.qnode(dev)
def f(x):
qml.RX(x["rx_param"], wires=0)
qml.RY(x["ry_param"], wires=0)
qml.CNOT(wires=[0, 1])
return {
"XY": qml.expval(qml.X(0) @ qml.Y(1)),
"X": qml.expval(qml.X(0)),
}
>>> x = {"rx_param": 0.5, "ry_param": 0.54}
>>> f(x)
{'X': array(-0.75271018), 'XY': array(1.)}
For more details on using the :func:`~.qjit` decorator and Catalyst
with PennyLane, please refer to the Catalyst
:doc:`quickstart guide <catalyst:dev/quick_start>`,
as well as the :doc:`sharp bits and debugging tips <catalyst:dev/sharp_bits>`
page for an overview of the differences between Catalyst and PennyLane, and
how to best structure your workflows to improve performance when
using Catalyst.
.. details::
:title: Static arguments
``static_argnums`` defines which elements should be treated as static. If it takes an
integer, it means the argument whose index is equal to the integer is static. If it takes
an iterable of integers, arguments whose index is contained in the iterable are static.
Changing static arguments will trigger re-compilation.
A valid static argument must be hashable and its ``__hash__`` method must be able to
reflect any changes of its attributes.
.. code-block:: python
@dataclass
class MyClass:
val: int
def __hash__(self):
return hash(str(self))
@qjit(static_argnums=1)
def f(
x: int,
y: MyClass,
):
return x + y.val
f(1, MyClass(5))
f(1, MyClass(6)) # re-compilation
f(2, MyClass(5)) # no re-compilation
In the example above, ``y`` is static. Note that the second function call triggers
re-compilation since the input object is different from the previous one. However,
the third function call directly uses the previous compiled one and does not introduce
re-compilation.
.. code-block:: python
@dataclass
class MyClass:
val: int
def __hash__(self):
return hash(str(self))
@qjit(static_argnums=(1, 2))
def f(
x: int,
y: MyClass,
z: MyClass,
):
return x + y.val + z.val
my_obj_1 = MyClass(5)
my_obj_2 = MyClass(6)
f(1, my_obj_1, my_obj_2)
my_obj_1.val = 7
f(1, my_obj_1, my_obj_2) # re-compilation
In the example above, ``y`` and ``z`` are static. The second function will cause
function ``f`` to re-compile because ``my_obj_1`` is changed. This requires that
the mutation is properly reflected in the hash value.
Note that when ``static_argnums`` is used in conjunction with type hinting,
ahead-of-time compilation will not be possible since the static argument values
are not yet available. Instead, compilation will be just-in-time.
.. details::
:title: Dynamically-shaped arrays
There are three ways to use ``abstracted_axes``; by passing a sequence of tuples, a
dictionary, or a sequence of dictionaries. Passing a sequence of tuples:
.. code-block:: python
abstracted_axes=((), ('n',), ('m', 'n'))
Each tuple in the sequence corresponds to one of the arguments in the annotated
function. Empty tuples can
be used and correspond to parameters with statically known shapes.
Non-empty tuples correspond to parameters with dynamically known shapes.
In this example above,
- the first argument will have a statically known shape,
- the second argument will have dynamic
shape ``n`` for the zeroth axis, and
- the third argument will have dynamic shape
``m`` for its zeroth axis and dynamic shape ``n`` for
its first axis.
Passing a dictionary:
.. code-block:: python
abstracted_axes={0: 'n'}
This approach allows a concise expression of the relationships
between axes for different function arguments. In this example,
it specifies that for all function arguments, the zeroth axis will
have dynamic shape ``n``.
Passing a sequence of dictionaries:
.. code-block:: python
abstracted_axes=({}, {0: 'n'}, {1: 'm', 0: 'n'})
The example here is a more verbose version of the tuple example. This convention
allows axes to be omitted from the list of abstracted axes.
Using ``abstracted_axes`` can help avoid the cost of recompilation.
By using ``abstracted_axes``, a more general version of the compiled function will be
generated. This more general version is parametrized over the abstracted axes and
allows results to be computed over tensors independently of their axes lengths.
For example:
.. code-block:: python
@qjit
def sum(arr):
return jnp.sum(arr)
sum(jnp.array([1])) # Compilation happens here.
sum(jnp.array([1, 1])) # And here!
The ``sum`` function would recompile each time an array of different size is passed
as an argument.
.. code-block:: python
@qjit(abstracted_axes={0: "n"})
def sum_abstracted(arr):
return jnp.sum(arr)
sum(jnp.array([1])) # Compilation happens here.
sum(jnp.array([1, 1])) # No need to recompile.
The ``sum_abstracted`` function would only compile once and its definition would be
reused for subsequent function calls.
"""
if not available(compiler):
raise CompileError(f"The {compiler} package is not installed.") # pragma: no cover
# Check the minimum version of 'compiler' if installed
_check_compiler_version(compiler)
compilers = AvailableCompilers.names_entrypoints
qjit_loader = compilers[compiler]["qjit"].load()
return qjit_loader(fn=fn, *args, **kwargs)
[docs]def while_loop(cond_fn):
"""A :func:`~.qjit` compatible while-loop for PennyLane programs.
.. note::
This function only supports the Catalyst compiler. See
:func:`catalyst.while_loop` for more details.
Please see the Catalyst :doc:`quickstart guide <catalyst:dev/quick_start>`,
as well as the :doc:`sharp bits and debugging tips <catalyst:dev/sharp_bits>`
page for an overview of the differences between Catalyst and PennyLane.
This decorator provides a functional version of the traditional while
loop, similar to `jax.lax.while_loop <https://jax.readthedocs.io/en/latest/_autosummary/jax.lax.while_loop.html>`__.
That is, any variables that are modified across iterations need to be provided as
inputs and outputs to the loop body function:
- Input arguments contain the value of a variable at the start of an
iteration
- Output arguments contain the value at the end of the iteration. The
outputs are then fed back as inputs to the next iteration.
The final iteration values are also returned from the
transformed function.
The semantics of ``while_loop`` are given by the following Python pseudo-code:
.. code-block:: python
def while_loop(cond_fn, body_fn, *args):
while cond_fn(*args):
args = body_fn(*args)
return args
Args:
cond_fn (Callable): the condition function in the while loop
Returns:
Callable: A wrapper around the while-loop function.
Raises:
CompileError: if the compiler is not installed
.. seealso:: :func:`~.for_loop`, :func:`~.qjit`
**Example**
.. code-block:: python
dev = qml.device("lightning.qubit", wires=1)
@qml.qjit
@qml.qnode(dev)
def circuit(x: float):
@qml.while_loop(lambda x: x < 2.0)
def loop_rx(x):
# perform some work and update (some of) the arguments
qml.RX(x, wires=0)
return x ** 2
# apply the while loop
final_x = loop_rx(x)
return qml.expval(qml.Z(0)), final_x
>>> circuit(1.6)
(array(-0.02919952), array(2.56))
"""
if active_jit := active_compiler():
compilers = AvailableCompilers.names_entrypoints
ops_loader = compilers[active_jit]["ops"].load()
return ops_loader.while_loop(cond_fn)
raise CompileError("There is no active compiler package.") # pragma: no cover
[docs]def for_loop(lower_bound, upper_bound, step):
"""A :func:`~.qjit` compatible for-loop for PennyLane programs.
.. note::
This function only supports the Catalyst compiler. See
:func:`catalyst.for_loop` for more details.
Please see the Catalyst :doc:`quickstart guide <catalyst:dev/quick_start>`,
as well as the :doc:`sharp bits and debugging tips <catalyst:dev/sharp_bits>`
page for an overview of the differences between Catalyst and PennyLane.
This decorator provides a functional version of the traditional
for-loop, similar to `jax.cond.fori_loop <https://jax.readthedocs.io/en/latest/_autosummary/jax.lax.fori_loop.html>`__.
That is, any variables that are modified across iterations need to be provided
as inputs/outputs to the loop body function:
- Input arguments contain the value of a variable at the start of an
iteration.
- output arguments contain the value at the end of the iteration. The
outputs are then fed back as inputs to the next iteration.
The final iteration values are also returned from the transformed
function.
The semantics of ``for_loop`` are given by the following Python pseudo-code:
.. code-block:: python
def for_loop(lower_bound, upper_bound, step, loop_fn, *args):
for i in range(lower_bound, upper_bound, step):
args = loop_fn(i, *args)
return args
Unlike ``jax.cond.fori_loop``, the step can be negative if it is known at tracing time
(i.e., constant). If a non-constant negative step is used, the loop will produce no iterations.
Args:
lower_bound (int): starting value of the iteration index
upper_bound (int): (exclusive) upper bound of the iteration index
step (int): increment applied to the iteration index at the end of each iteration
Returns:
Callable[[int, ...], ...]: A wrapper around the loop body function.
Note that the loop body function must always have the iteration index as its first
argument, which can be used arbitrarily inside the loop body. As the value of the index
across iterations is handled automatically by the provided loop bounds, it must not be
returned from the function.
Raises:
CompileError: if the compiler is not installed
.. seealso:: :func:`~.while_loop`, :func:`~.qjit`
**Example**
.. code-block:: python
dev = qml.device("lightning.qubit", wires=1)
@qml.qjit
@qml.qnode(dev)
def circuit(n: int, x: float):
@qml.for_loop(0, n, 1)
def loop_rx(i, x):
# perform some work and update (some of) the arguments
qml.RX(x, wires=0)
# update the value of x for the next iteration
return jnp.sin(x)
# apply the for loop
final_x = loop_rx(x)
return qml.expval(qml.Z(0)), final_x
>>> circuit(7, 1.6)
(array(0.97926626), array(0.55395718))
"""
if active_jit := active_compiler():
compilers = AvailableCompilers.names_entrypoints
ops_loader = compilers[active_jit]["ops"].load()
return ops_loader.for_loop(lower_bound, upper_bound, step)
raise CompileError("There is no active compiler package.") # pragma: no cover
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