Add MinimumPoint transpiler pass #9612

mtreinish · 2023-02-17T17:38:02Z

Summary

This commit adds a new transpiler pass MinimumPoint which is used to find a local minimum point from the property set between executions of the pass. This is similar to the existing FixedPoint pass but will find the minimum fixed point over the past n exeuctions as opposed to finding a when two subsequent exectuions are at the same point. This is then used in optimization level 3 because the 2q unitary synthesis optimization that is part of the optimization loop can occasionally get stuck oscillating between multiple different equivalent decompositions which prevents the fixed point condition from ever being reached. By checking that we've reached the minimum over the last 5 executions we ensure we're reaching an exit condition in this situation.

Details and comments

Fixes #5832
Fixes #9177
Fixes #9776

(the underlying cause of the optimization loop's inability to converge at optimization level 3 is not fixed here, there is still a root cause of instability in UnitarySynthesis this just changes the loop exit condition so we're never stuck in an infinte loop)

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coveralls · 2023-02-17T18:03:21Z

Pull Request Test Coverage Report for Build 4565674227

45 of 45 (100.0%) changed or added relevant lines in 4 files are covered.
No unchanged relevant lines lost coverage.
Overall coverage decreased (-0.01%) to 85.367%

Totals
Change from base Build 4564463001:	-0.01%
Covered Lines:	67151
Relevant Lines:	78662

💛 - Coveralls

test/python/compiler/test_transpiler.py

qiskit/transpiler/passes/utils/minimum_point.py

1ucian0 · 2023-03-11T14:10:40Z

qiskit/transpiler/passes/utils/minimum_point.py

+     * ``{prefix}_minimum_point_count`` - Used to track the number of executions since
+        the current minimum was found
+     * ``{prefix}_backtrack_history`` - Stores the current minimum value and :class:`~.DAGCircuit`
+     * ``{prefix}_minimum_point`` - This value gets set to ``True`` when either a fixed point
+        is reached over the ``backtrack_depth`` executions, or ``backtrack_depth`` was exceeded
+        and an earlier minimum is restored.
+    """


This bullet list seems to not render correctly:

there's an extra space in the indentation, which is causing it to be parsed as a bullet point containing a single-item definition list

test/python/transpiler/test_minimum_point.py

jakelishman

I'm happy with the logic of what this PR is trying to accomplish, and I'm happy that it'll be superior to what we've got in place already, although maybe we should replace all use of FixedPoint with this - it feels like an accident waiting to happen in other places too. My issues are mostly just with legibility - the logic is quite tricksy, so I think it's important that we put a good amount of effort into making both it and its tests as readable as possible.

qiskit/transpiler/passes/utils/minimum_point.py

test/python/compiler/test_transpiler.py

jakelishman · 2023-03-13T17:17:42Z

test/python/transpiler/test_minimum_point.py

+    def test_min_reset_backtrack_range(self):
+        """Test minimum resets backtrack depth."""
+        min_pass = MinimumPoint(["fidelity", "depth", "size"], prefix="test")
+        dag = DAGCircuit()
+        min_pass.property_set["fidelity"] = 0.875
+        min_pass.property_set["depth"] = 15
+        min_pass.property_set["size"] = 20
+        min_pass.run(dag)
+        self.assertEqual(min_pass.property_set["test_minimum_point_count"], 1)
+        self.assertIsNone(min_pass.property_set["test_backtrack_history"])
+        self.assertIsNone(min_pass.property_set["test_min_point"])


Some of the assertions in these tests feel rather like testing relatively minor implementation details, like the exact objects we expect are tracked with very specific names in the property set.

Leaving that aside, though, the test is quite hard to quickly check what the sequence of values are being set as the properties; for something like this, I think it's maybe easier if we could define the sequence of inserted values and expected values up in single lists at the top of the test so all the context is localised, then loop through them.

I left the tests mostly in place like this primarily to make it explicit what is happening in each iteration. I worry the details of the exact logic flow would be lost with a for loop. Especially given the complexity of the logic going on here my thinking was it might be difficult to track and testing it explicitly like this made it easier for me to ensure I got the expected logic. I agree that it does end up being a bit repetitive and a bit too detailed. In e2c8cd0 I added a bunch of comments to each iteration to explain the context.

This commit adds a new transpiler pass MinimumPoint which is used to find a local minimum point from the property set between executions of the pass. This is similar to the existing FixedPoint pass but will find the minimum fixed point over the past n exeuctions as opposed to finding a when two subsequent exectuions are at the same point. This is then used in optimization level 3 because the 2q unitary synthesis optimization that is part of the optimization loop can occasionally get stuck oscillating between multiple different equivalent decompositions which prevents the fixed point condition from ever being reached. By checking that we've reached the minimum over the last 5 executions we ensure we're reaching an exit condition in this situation. Fixes Qiskit#5832 Fixes Qiskit#9177 (the underlying cause of the optimization loop's inability to converge at optimization level 3 is not fixed here, there is still a root cause of instability in UnitarySynthesis this just changes the loop exit condition so we're never stuck in an infinte loop)

This commit reworks the logic of the pass to track the state via a dataclass instead of using separate property set fields. This cleans up the code for dealing with checking the current state relative to earlier iterations by making the access just attributes instead of secret strings. At the same time the tests were updated to handle this new data structure comments were added to better explain the logic flow being tested.

jakelishman

The slots thing is Python 3.10+ only, but with that and the minor grammar tweaks in the comments for better legibility, this looks good to me. The comments help a lot, and I think you're probably right about not wanting to do things in a loop in the tests.

qiskit/transpiler/passes/utils/minimum_point.py

test/python/transpiler/test_minimum_point.py

Co-authored-by: Jake Lishman <jake@binhbar.com>

jakelishman

Ace, thanks!

* Add MinimumPoint transpiler pass This commit adds a new transpiler pass MinimumPoint which is used to find a local minimum point from the property set between executions of the pass. This is similar to the existing FixedPoint pass but will find the minimum fixed point over the past n exeuctions as opposed to finding a when two subsequent exectuions are at the same point. This is then used in optimization level 3 because the 2q unitary synthesis optimization that is part of the optimization loop can occasionally get stuck oscillating between multiple different equivalent decompositions which prevents the fixed point condition from ever being reached. By checking that we've reached the minimum over the last 5 executions we ensure we're reaching an exit condition in this situation. Fixes Qiskit#5832 Fixes Qiskit#9177 (the underlying cause of the optimization loop's inability to converge at optimization level 3 is not fixed here, there is still a root cause of instability in UnitarySynthesis this just changes the loop exit condition so we're never stuck in an infinte loop) * Doc copy-paste error cleanups * Rework logic to track state with a dataclass This commit reworks the logic of the pass to track the state via a dataclass instead of using separate property set fields. This cleans up the code for dealing with checking the current state relative to earlier iterations by making the access just attributes instead of secret strings. At the same time the tests were updated to handle this new data structure comments were added to better explain the logic flow being tested. * Fix doc typo * Apply suggestions from code review Co-authored-by: Jake Lishman <jake@binhbar.com> * Update slots syntax for dataclass to be compatible with Python < 3.10 * Update property set check in tests --------- Co-authored-by: Jake Lishman <jake@binhbar.com>

mtreinish added Changelog: New Feature Include in the "Added" section of the changelog mod: transpiler Issues and PRs related to Transpiler labels Feb 17, 2023

mtreinish added this to the 0.24.0 milestone Feb 17, 2023

mtreinish requested a review from a team as a code owner February 17, 2023 17:38

1ucian0 self-assigned this Feb 22, 2023

1ucian0 reviewed Mar 3, 2023

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jakelishman mentioned this pull request Mar 10, 2023

Max iteration being hit on QV circuits targetting ECR-based systems #9776

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1ucian0 reviewed Mar 11, 2023

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jakelishman reviewed Mar 13, 2023

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mtreinish added 3 commits March 29, 2023 10:28

Doc copy-paste error cleanups

8e96ad7

mtreinish force-pushed the minimum-point-pass branch from 44b6b4e to e2c8cd0 Compare March 29, 2023 15:31

Fix doc typo

3f74311

jakelishman reviewed Mar 29, 2023

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mtreinish and others added 4 commits March 30, 2023 10:31

Apply suggestions from code review

e603007

Co-authored-by: Jake Lishman <jake@binhbar.com>

Update slots syntax for dataclass to be compatible with Python < 3.10

a339bb1

Update property set check in tests

f889fbd

Merge remote-tracking branch 'origin/main' into minimum-point-pass

0581884

jakelishman approved these changes Mar 30, 2023

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jakelishman enabled auto-merge March 30, 2023 14:45

jakelishman linked an issue Mar 30, 2023 that may be closed by this pull request

Max iteration being hit on QV circuits targetting ECR-based systems #9776

Closed

jakelishman added this pull request to the merge queue Mar 30, 2023

Merged via the queue into Qiskit:main with commit 694ade4 Mar 30, 2023

jakelishman mentioned this pull request Aug 22, 2023

Optimization stage as a plugin. #10581

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Add MinimumPoint transpiler pass #9612

Add MinimumPoint transpiler pass #9612

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Add MinimumPoint transpiler pass #9612

Add MinimumPoint transpiler pass #9612

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mtreinish commented Feb 17, 2023 • edited Loading

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Pull Request Test Coverage Report for Build 4565674227

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