HLS fix to not synthesize instructions already supported

[alexanderivrii]

Summary

Fixes #13412.

Needs to be backported to 1.3.0.

Details and comments

Previously HighLevelSynthesis synthesized an instruction for which a synthesis plugin was available, even when the instruction was already considered supported (either supported by the target or a part of basis_gates). This commit fixes this behavior.
Update: the control-flow operations (e.g. for-loop) belong to basis_gates but need to be recursively synthesized.

Even though the problem was only discovered for "PauliEvolution" gates also added for 1.3, the incorrect behavior for other high-level gates existed before, so I added release notes. I was not sure if they should be under releasenotes/notes/1.3 or not.

[qiskit-bot]

One or more of the following people are relevant to this code:

• @Qiskit/terra-core

[coveralls]

Pull Request Test Coverage Report for Build 11813177643

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

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Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 35 unchanged lines in 4 files lost coverage.
• Overall coverage decreased (-0.02%) to 88.911%

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Files with Coverage Reduction	New Missed Lines	%
crates/accelerate/src/unitary_synthesis.rs	1	92.2%
crates/qasm2/src/lex.rs	4	91.98%
qiskit/transpiler/passes/synthesis/high_level_synthesis.py	12	92.94%
crates/qasm2/src/parse.rs	18	96.69%

Totals
Change from base Build 11749692210:	-0.02%
Covered Lines:	79044
Relevant Lines:	88902

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💛 - Coveralls

[Cryoris]

Just to double check: this bug with PauliEvolution only came up in 1.3, but already in 1.2 this was wrong. However, we didn't notice with PauliEvolution gate though, since we didn't have plugins, but it could've been triggered with something else, right?

[alexanderivrii]

Yes, exactly!

[Cryoris]

LGTM for this fix, thank you!

However, I’m mildly unhappy about that special treatment of control flow… there’s somehow a different meaning to basis gates. Usually a name being in basis_gates means we can run it, but for control_flow that’s not quite true, since we still need to synthesize it’s insides 🤔

[alexanderivrii]

However, I’m mildly unhappy about that special treatment of control flow… there’s somehow a different meaning to basis gates. Usually a name being in basis_gates means we can run it, but for control_flow that’s not quite true, since we still need to synthesize it’s insides 🤔

Thanks @Cryoris! I completely agree, I would also like to see a better separation between gates and between control-flow logic. However, for the purpose of the bug fix. Is there anything specific I should do?

[Cryoris]

No I agree this is the correct fix for now, this was more a comment to discuss this in general later on 🙂