Bug in Timing/Frame Dependencies

[kalzoo]

Hot on the heels of #73 , another bug has been found in how frame blocking is calculated. Two examples are given here, with further explanation below. Can you spot the bug?

Example 1

Hint: there is an additional frame defined in the program, 0 1 "cz", which is not used by any of the instructions.

Example 2

The problem here is that the change in #73 properly fixed how dependencies are calculated after a blocking instruction, but that blocking instruction must itself block on previous instructions which overlap in frames, and that is not happening.

Specifically/formally:

1. An instruction which uses a frame must depend on the most-recent user and blockers of the frame, if any. Doing so clears all blockers of the frame and this instruction becomes the most-recent user.
2. An instruction which blocks but does not use a frame must depend on the most-recent user of the frame. Doing so leaves the most-recent user in place and adds this instruction to a list of most-recent blockers.

Blocking prevents simultaneous use but allows simultaneous blocking.

This approach is akin to a single-writer, multiple-reader lock or queue, where blocking:reading::using:writing.

[notmgsk]

Just seeing if I understand the issue:

• In example 1, the problem is the frame dependency between the start and [1] PULSE 1 "rf" nodes?
• In example 2, the problem is the missing frame dependency between nodes [1] and [3]?

[kalzoo]

Example 1 - yep. Example 2 - close! Dependency missing between 1 & 2

[notmgsk]

Oh -- 2 is your issue with the quil-spec?

[notmgsk]

Admittedly, I didn't think of that problem because I have come to see NONBLOCKING as having an effect on the following instructions.

[kalzoo]

Oh -- 2 is your issue with the quil-spec?

It’s similar but not quite the same because they do in fact share the used frame. (That being said, I think that might have been a typo in building this example, so in reality yes that might be what I meant to illustrate).

[github-actions]

🎉 This issue has been resolved in version 0.11.0 🎉

The release is available on:

• crate.io packages (1 packages published)
• GitHub release

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