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Qiskit
add controlflow handling to Layout2qDistance transpiler pass
Summary
This pr adds controlflow handling to the Layout2qDistance transpiler pass.
Details and comments
This implementation adds an init parameter weight_loops to indicate whether the number of blocks/loops should contribute to the overall 2q layout score. If True for while loops, NaN is returned.
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Pull Request Test Coverage Report for Build 3040745492
- 26 of 29 (89.66%) changed or added relevant lines in 1 file are covered.
- No unchanged relevant lines lost coverage.
- Overall coverage increased (+0.005%) to 84.309%
| Changes Missing Coverage | Covered Lines | Changed/Added Lines | % |
|---|---|---|---|
| qiskit/transpiler/passes/layout/layout_2q_distance.py | 26 | 29 | 89.66% |
| <!-- | Total: | 26 | 29 |
| Totals | |
|---|---|
| Change from base Build 3039251673: | 0.005% |
| Covered Lines: | 57854 |
| Relevant Lines: | 68621 |
💛 - Coveralls
I tend to agree, the 2q distance does seem like overkill for determining that a trivial layout is perfect. CheckMap is more than enough to determine if the trivial layout is enough and should be faster. I'm not sure the history on the use of Layout2qDistance for this either, I never really questioned its usage when I touched the layout path code in the past, but from my perspective making that switch in level1 makes the most sense to me. (it's not used in level 2 or 3 because vf2layout does the checking for us)
On its own this pass proposes to score the quality of a layout in a reasonable way. Whether or not other passes use this analysis is a somewhat separate issue, although it doesn't seem like anything in terra currently use this information in a way that can't be replaced by CheckMap as pointed out.
In the case of level1 it seems fine to replace this pass with CheckMap, put this PR on hold, and perhaps deprecate the pass.