Track qubit live-ness during simulation #2020

swernli · 2024-11-13T19:12:31Z

This change adds some basic qubit live-ness tracking to the simulator, achieved by changing the Value::Qubit variant to a weak pointer to the qubit and having the execution environment own and track the Rc that owns the qubit. This provides a few benefits:

Fixes a panic when a qubit is passed to the simulator after it has been released.
Adds graceful error handling to treat use-after-release as a runtime error.
Adds a specific error for "double release" of a qubit if it is being manually managed.
Updates the display of the qubit type to show the qubit ID when it is live and Qubit<released> when it is not, enabling easier debugging of qubit lifetimes.

Of note, local perf testing showing no impact on performance (thanks, Rust zero-cost abstractions!), though it stands to reason this change could theoretically have some impact on programs that use many thousands of qubits.

This change adds some basic qubit live-ness tracking to the simulator, achieved by changing the `Value::Qubit` variant to a weak pointer to the qubit and having the execution environment own and track the `Rc` that owns the qubit. This provides a few benefits: - Fixes a panic when a qubit is passed to the simulator after it has been released. - Adds graceful error handling to treat use-after-release as a runtime error. - Adds a specific error for "double release" of a qubit if it is being manually managed. - Updates the display of the qubit type to show the qubit ID when it is live and `Qubit<released>` when it is not, enabling easier debugging of qubit lifetimes. Of note, local perf testing showing no impact on performance (thanks, Rust zero-cost abstractions!), though it stands to reason this change could theoretically have some impact on programs that use many thousands of qubits.

compiler/qsc_eval/src/lib.rs

minestarks

live-ness

I feel like the word you're looking for is "lifetime"?

compiler/qsc_eval/src/lib.rs

compiler/qsc_eval/src/val.rs

compiler/qsc_partial_eval/src/management.rs

compiler/qsc_partial_eval/src/lib.rs

compiler/qsc_eval/src/intrinsic.rs

compiler/qsc_partial_eval/src/lib.rs

sezna

Big fan of QubitRef

swernli requested review from billti, ivanbasov, idavis and minestarks as code owners November 13, 2024 19:12

github-advanced-security bot found potential problems Nov 13, 2024

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compiler/qsc_eval/src/lib.rs Fixed Show fixed Hide fixed

Remove leftover todo comment

000ddc1

minestarks reviewed Nov 13, 2024

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compiler/qsc_eval/src/lib.rs Show resolved Hide resolved

Use explicit Weak::clone

b0c257b

minestarks approved these changes Nov 14, 2024

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