Avoid private methods when adding unused `Parameter`s #34

jakelishman · 2024-06-04T13:42:33Z

Using private methods of QuantumCircuit to force tracking of unused Parameter instances resulting in the cleanest circuit output, but was fragile against Qiskit changing the private data structure internals. This has been a real problem as Qiskit moves more of the internal data tracking down to Rust space.

This changes the hacked-in tracking to use only public methods to insert a dummy reference, at the cost that a true reference is added in to the global phase. For most real-world uses of unused parameters (i.e. those in gate bodies), this will immediately be assigned out and so be invisible to users. The only place where this should appear to users is if there is an input float that is unused. In these cases, a dummy reference will be inserted into the global phase that has no effect.

Fix #33.

Using private methods of `QuantumCircuit` to force tracking of unused `Parameter` instances resulting in the cleanest circuit output, but was fragile against Qiskit changing the private data structure internals. This has been a real problem as Qiskit moves more of the internal data tracking down to Rust space. This changes the hacked-in tracking to use only public methods to insert a dummy reference, at the cost that a _true_ reference is added in to the global phase. For most real-world uses of unused parameters (i.e. those in gate bodies), this will immediately be assigned out and so be invisible to users. The only place where this should appear to users is if there is an `input float` that is unused. In these cases, a dummy reference will be inserted into the global phase that has no effect.

mtreinish

LGTM, thanks for doing this so quickly

mtreinish · 2024-06-04T15:05:06Z

src/qiskit_qasm3_import/state.py

+    # they're not all there.  This uses the fact that `parameter - parameter` is a
+    # `ParameterExpression` representation of zero that still tracks that it was once
+    # parametric over `parameter`.
+    circuit.global_phase += parameter - parameter


I guess this potentially does change the type of global phase from a float to parameter expression in Qiskit which is a bit unfortunate. But it should be normalized away if somebody does anything that uses the circuit for anything and global phase gets cast as a float.

Yeah, it does, and what's worse, it makes the global phase compare unequal to 0 (because of the parametrisation). But it should only actually appear for OQ3 programs like

input float a;

where a isn't used, and I think storing the dummy reference in the global phase is probably less disruptive than adding a dummy gate to hold it.

In Qiskit/qiskit-qasm3-import#34 the issue we're hitting caused by qiskit-qasm3-import using the private circuit attributes removed in this PR was fixed. This commit temporarily moves to installing it from git so we can fully run CI. When qiskit-qasm3-import is released we should revert this commit.

…2459) * Add infrastructure for gates, instruction, and operations in Rust This commit adds a native representation of Gates, Instruction, and Operations to rust's circuit module. At a high level this works by either wrapping the Python object in a rust wrapper struct that tracks metadata about the operations (name, num_qubits, etc) and then for other details it calls back to Python to get dynamic details like the definition, matrix, etc. For standard library gates like Swap, CX, H, etc this replaces the on-circuit representation with a new rust enum StandardGate. The enum representation is much more efficient and has a minimal memory footprint (just the enum variant and then any parameters or other mutable state stored in the circuit instruction). All the gate properties such as the matrix, definiton, name, etc are statically defined in rust code based on the enum variant (which represents the gate). The use of an enum to represent standard gates does mean a change in what we store on a CircuitInstruction. To represent a standard gate fully we need to store the mutable properties of the existing Gate class on the circuit instruction as the gate by itself doesn't contain this detail. That means, the parameters, label, unit, duration, and condition are added to the rust side of circuit instrucion. However no Python side access methods are added for these as they're internal only to the Rust code. In Qiskit 2.0 to simplify this storage we'll be able to drop, unit, duration, and condition from the api leaving only label and parameters. But for right now we're tracking all of the fields. To facilitate working with circuits and gates full from rust the setting the `operation` attribute of a `CircuitInstruction` object now transltates the python object to an internal rust representation. For standard gates this translates it to the enum form described earlier, and for other circuit operations 3 new Rust structs: PyGate, PyInstruction, and PyOperation are used to wrap the underlying Python object in a Rust api. These structs cache some commonly accessed static properties of the operation, such as the name, number of qubits, etc. However for dynamic pieces, such as the definition or matrix, callback to python to get a rust representation for those. Similarly whenever the `operation` attribute is accessed from Python it converts it back to the normal Python object representation. For standard gates this involves creating a new instance of a Python object based on it's internal rust representation. For the wrapper structs a reference to the wrapped PyObject is returned. To manage the 4 variants of operation (`StandardGate`, `PyGate`, `PyInstruction`, and `PyOperation`) a new Rust trait `Operation` is created that defines a standard interface for getting the properties of a given circuit operation. This common interface is implemented for the 4 variants as well as the `OperationType` enum which wraps all 4 (and is used as the type for `CircuitInstruction.operation` in the rust code. As everything in the `QuantumCircuit` data model is quite coupled moving the source of truth for the operations to exist in Rust means that more of the underlying `QuantumCircuit`'s responsibility has to move to Rust as well. Primarily this involves the `ParameterTable` which was an internal class for tracking which instructions in the circuit have a `ParameterExpression` parameter so that when we go to bind parameters we can lookup which operations need to be updated with the bind value. Since the representation of those instructions now lives in Rust and Python only recieves a ephemeral copy of the instructions the ParameterTable had to be reimplemented in Rust to track the instructions. This new parameter table maps the Parameter's uuid (as a u128) as a unique identifier for each parameter and maps this to a positional index in the circuit data to the underlying instruction using that parameter. This is a bit different from the Python parameter table which was mapping a parameter object to the id of the operation object using that parmaeter. This also leads to a difference in the binding mechanics as the parameter assignment was done by reference in the old model, but now we need to update the entire instruction more explicitly in rust. Additionally, because the global phase of a circuit can be parameterized the ownership of global phase is moved from Python into Rust in this commit as well. After this commit the only properties of a circuit that are not defined in Rust for the source of truth are the bits (and vars) of the circuit, and when creating circuits from rust this is what causes a Python interaction to still be required. This commit does not translate the full standard library of gates as that would make the pull request huge, instead this adds the basic infrastructure for having a more efficient standard gate representation on circuits. There will be follow up pull requests to add the missing gates and round out support in rust. The goal of this pull request is primarily to add the infrastructure for representing the full circuit model (and dag model in the future) in rust. By itself this is not expected to improve runtime performance (if anything it will probably hurt performance because of extra type conversions) but it is intended to enable writing native circuit manipulations in Rust, including transpiler passes without needing involvement from Python. Longer term this should greatly improve the runtime performance and reduce the memory overhead of Qiskit. But, this is just an early step towards that goal, and is more about unlocking the future capability. The next steps after this commit are to finish migrating the standard gate library and also update the `QuantumCircuit` methods to better leverage the more complete rust representation (which should help offset the performance penalty introduced by this). Fixes: #12205 * Fix Python->Rust Param conversion This commit adds a custom implementation of the FromPyObject trait for the Param enum. Previously, the Param trait derived it's impl of the trait, but this logic wasn't perfect. In cases whern a ParameterExpression was effectively a constant (such as `0 * x`) the trait's attempt to coerce to a float first would result in those ParameterExpressions being dropped from the circuit at insertion time. This was a change in behavior from before having gates in Rust as the parameters would disappear from the circuit at insertion time instead of at bind time. This commit fixes this by having a custom impl for FromPyObject that first tries to figure out if the parameter is a ParameterExpression (or a QuantumCircuit) by using a Python isinstance() check, then tries to extract it as a float, and finally stores a non-parameter object; which is a new variant in the Param enum. This new variant also lets us simplify the logic around adding gates to the parameter table as we're able to know ahead of time which gate parameters are `ParameterExpression`s and which are other objects (and don't need to be tracked in the parameter table. Additionally this commit tweaks two tests, the first is test.python.circuit.library.test_nlocal.TestNLocal.test_parameters_setter which was adjusted in the previous commit to workaround the bug fixed by this commit. The second is test.python.circuit.test_parameters which was testing that a bound ParameterExpression with a value of 0 defaults to an int which was a side effect of passing an int input to symengine for the bind value and not part of the api and didn't need to be checked. This assertion was removed from the test because the rust representation is only storing f64 values for the numeric parameters and it is never an int after binding from the Python perspective it isn't any different to have float(0) and int(0) unless you explicit isinstance check like the test previously was. * Fix qasm3 exporter for std gates without stdgates.inc This commit fixes the handling of standard gates in Qiskit when the user specifies excluding the use of the stdgates.inc file from the exported qasm. Previously the object id of the standard gates were used to maintain a lookup table of the global definitions for all the standard gates explicitly in the file. However, the rust refactor means that every time the exporter accesses `circuit.data[x].operation` a new instance is returned. This means that on subsequent lookups for the definition the gate definitions are never found. To correct this issue this commit adds to the lookup table a fallback of the gate name + parameters to do the lookup for. This should be unique for any standard gate and not interfere with the previous logic that's still in place and functional for other custom gate definitions. While this fixes the logic in the exporter the test is still failing because the test is asserting the object ids are the same in the qasm3 file, which isn't the case anymore. The test will be updated in a subsequent commit to validate the qasm3 file is correct without using a hardcoded object id. * Fix base scheduler analysis pass duration setting When ALAPScheduleAnalysis and ASAPScheduleAnalysis were setting the duration of a gate they were doing `node.op.duration = duration` this wasn't always working because if `node.op` was a standard gate it returned a new Python object created from the underlying rust representation. This commit fixes the passes so that they modify the duration and then explicit set the operation to update it's rust representation. * Fix python lint * Fix last failing qasm3 test for std gates without stdgates.inc While the logic for the qasm3 exporter was fixed in commit a6e69ba to handle the edge case of a user specifying that the qasm exporter does not use the stdgates.inc include file in the output, but also has qiskit's standard gates in their circuit being exported. The one unit test to provide coverage for that scenario was not passing because when an id was used for the gate definitions in the qasm3 file it was being referenced against a temporary created by accessing a standard gate from the circuit and the ids weren't the same so the reference string didn't match what the exporter generated. This commit fixes this by changing the test to not do an exact string comparison, but instead a line by line comparison that either does exact equality check or a regex search for the expected line and the ids are checked as being any 15 character integer. * Remove superfluous comment * Cache imported classes with GILOnceCell * Remove unused python variables * Add missing file * Update QuantumCircuit gate methods to bypass Python object This commit updates the QuantumCircuit gate methods which add a given gate to the circuit to bypass the python gate object creation and directly insert a rust representation of the gate. This avoids a conversion in the rust side of the code. While in practice this is just the Python side object creation and a getattr for the rust code to determine it's a standard gate that we're skipping. This may add up over time if there are a lot of gates being created by the method. To accomplish this the rust code handling the mapping of rust StandardGate variants to the Python classes that represent those gates needed to be updated as well. By bypassing the python object creation we need a fallback to populate the gate class for when a user access the operation object from Python. Previously this mapping was only being populated at insertion time and if we never insert the python object (for a circuit created only via the methods) then we need a way to find what the gate class is. A static lookup table of import paths and class names are added to `qiskit_circuit::imports` module to faciliate this and helper functions are added to facilitate interacting with the class objects that represent each gate. * Deduplicate gate matrix definitions * Fix lint * Attempt to fix qasm3 test failure * Add compile time option to cache py gate returns for rust std gates This commit adds a new rust crate feature flag for the qiskit-circuits and qiskit-pyext that enables caching the output from CircuitInstruction.operation to python space. Previously, for memory efficiency we were reconstructing the python object on demand for every access. This was to avoid carrying around an extra pointer and keeping the ephemeral python object around longer term if it's only needed once. But right now nothing is directly using the rust representation yet and everything is accessing via the python interface, so recreating gate objects on the fly has a huge performance penalty. To avoid that this adds caching by default as a temporary solution to avoid this until we have more usage of the rust representation of gates. There is an inherent tension between an optimal rust representation and something that is performant for Python access and there isn't a clear cut answer on which one is better to optimize for. A build time feature lets the user pick, if what we settle on for the default doesn't agree with their priorities or use case. Personally I'd like to see us disable the caching longer term (hopefully before releasing this functionality), but that's dependent on a sufficent level of usage from rust superseding the current Python space usage in the core of Qiskit. * Add num_nonlocal_gates implementation in rust This commit adds a native rust implementation to rust for the num_nonlocal_gates method on QuantumCircuit. Now that we have a rust representation of gates it is potentially faster to do the count because the iteration and filtering is done rust side. * Performance tuning circuit construction This commit fixes some performance issues with the addition of standard gates to a circuit. To workaround potential reference cycles in Python when calling rust we need to check the parameters of the operation. This was causing our fast path for standard gates to access the `operation` attribute to get the parameters. This causes the gate to be eagerly constructed on the getter. However, the reference cycle case can only happen in situations without a standard gate, and the fast path for adding standard gates directly won't need to run this so a skip is added if we're adding a standard gate. * Add back validation of parameters on gate methods In the previous commit a side effect of the accidental eager operation creation was that the parameter input for gates were being validated by that. By fixing that in the previous commit the validation of input parameters on the circuit methods was broken. This commit fixes that oversight and adds back the validation. * Skip validation on gate creation from rust * Offload operation copying to rust This commit fixes a performance regression in the `QuantumCircuit.copy()` method which was previously using Python to copy the operations which had extra overhead to go from rust to python and vice versa. This moves that logic to exist in rust and improve the copy performance. * Fix lint * Perform deepcopy in rust This commit moves the deepcopy handling to occur solely in Rust. Previously each instruction would be directly deepcopied by iterating over the circuit data. However, we can do this rust side now and doing this is more efficient because while we need to rely on Python to run a deepcopy we can skip it for the Rust standard gates and rely on Rust to copy those gates. * Fix QuantumCircuit.compose() performance regression This commit fixes a performance regression in the compose() method. This was caused by the checking for classical conditions in the method requiring eagerly converting all standard gates to a Python object. This changes the logic to do this only if we know we have a condition (which we can determine Python side now). * Fix map_ops test case with no caching case * Fix typos in docs This commit fixes several docs typos that were caught during code review. Co-authored-by: Eli Arbel <[email protected]> * Shrink memory usage for extra mutable instruction state This commit changes how we store the extra mutable instruction state (condition, duration, unit, and label) for each `CircuitInstruction` and `PackedInstruction` in the circuit. Previously it was all stored as separate `Option<T>` fields on the struct, which required at least a pointer's width for each field which was wasted space the majority of the time as using these fields are not common. To optimize the memory layout of the struct this moves these attributes to a new struct which is put in an `Option<Box<_>>` which reduces it from 4 pointer widths down to 1 per object. This comes from extra runtime cost from the extra layer of pointer indirection but as this is the uncommon path this tradeoff is fine. * Remove Option<> from params field in CircuitInstruction This commit removes the Option<> from the params field in CircuitInstruction. There is no real distinction between an empty vec and None in this case, so the option just added another layer in the API that we didn't need to deal with. Also depending on the memory alignment using an Option<T> might have ended up in a little extra memory usage too, so removing it removes that potential source of overhead. * Eagerly construct rust python wrappers in .append() This commit updates the Python code in QuantumCircuit.append() method to eagerly construct the rust wrapper objects for python defined circuit operations. * Simplify code around handling python errors in rust * Revert "Skip validation on gate creation from rust" This reverts commit 2f81bde. The validation skipping was unsound in some cases and could lead to invalid circuit being generated. If we end up needing this as an optimization we can remove this in the future in a follow-up PR that explores this in isolation. * Temporarily use git for qasm3 import In Qiskit/qiskit-qasm3-import#34 the issue we're hitting caused by qiskit-qasm3-import using the private circuit attributes removed in this PR was fixed. This commit temporarily moves to installing it from git so we can fully run CI. When qiskit-qasm3-import is released we should revert this commit. * Fix lint * Fix lint for real (we really need to use a py312 compatible version of pylint) * Fix test failure caused by incorrect lint fix * Relax trait-method typing requirements * Encapsulate `GILOnceCell` initialisers to local logic * Simplify Interface for building circuit of standard gates in rust * Simplify complex64 creation in gate_matrix.rs This just switches Complex64::new(re, im) to be c64(re, im) to reduce the amount of typing. c64 needs to be defined inplace so it can be a const fn. * Simplify initialization of array of elements that are not Copy (#28) * Simplify initialization of array of elements that are not Copy * Only generate array when necessary * Fix doc typos Co-authored-by: Kevin Hartman <[email protected]> * Add conversion trait for OperationType -> OperationInput and simplify CircuitInstruction::replace() * Use destructuring for operation_type_to_py extra attr handling * Simplify trait bounds for map_indices() The map_indices() method previously specified both Iterator and ExactSizeIterator for it's trait bounds, but Iterator is a supertrait of ExactSizeIterator and we don't need to explicitly list both. This commit removes the duplicate trait bound. * Make Qubit and Clbit newtype member public As we start to use Qubit and Clbit for creating circuits from accelerate and other crates in the Qiskit workspace we need to be able to create instances of them. However, the newtype member BitType was not public which prevented creating new Qubits. This commit fixes this by making it public. * Use snakecase for gate matrix names * Remove pointless underscore prefix * Use downcast instead of bound * Rwork _append reference cycle handling This commit reworks the multiple borrow handling in the _append() method to leveraging `Bound.try_borrow()` to return a consistent error message if we're unable to borrow a CircuitInstruction in the rust code meaning there is a cyclical reference in the code. Previously we tried to detect this cycle up-front which added significant overhead for a corner case. * Make CircuitData.global_phase_param_index a class attr * Use &[Param] instead of &SmallVec<..> for operation_type_and_data_to_py * Have get_params_unsorted return a set * Use lookup table for static property methods of StandardGate * Use PyTuple::empty_bound() * Fix lint * Add missing test method docstring * Reuse allocations in parameter table update * Remove unnecessary global phase zeroing * Move manually set params to a separate function * Fix release note typo * Use constant for global-phase index * Switch requirement to release version --------- Co-authored-by: Eli Arbel <[email protected]> Co-authored-by: Jake Lishman <[email protected]> Co-authored-by: John Lapeyre <[email protected]> Co-authored-by: Kevin Hartman <[email protected]>

mtreinish approved these changes Jun 4, 2024

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jakelishman merged commit 8aafe7c into Qiskit:main Jun 5, 2024
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jakelishman deleted the parameter-hack branch June 5, 2024 07:42

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Avoid private methods when adding unused `Parameter`s #34

Avoid private methods when adding unused `Parameter`s #34

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Avoid private methods when adding unused Parameters #34

Avoid private methods when adding unused Parameters #34

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Avoid private methods when adding unused `Parameter`s #34

Avoid private methods when adding unused `Parameter`s #34