Qiskit / qiskit / 26948478985

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Add additional Z and X rotation gate handling to CommutativeCancellation (#16191)

* Add additional Z and X rotation gate handling to CommutativeCancellation

This commit expands the the handling of Z and X rotations to the
commutative cancellation pass to cover missing gates that it could
easily handle. In addition for the output rotation gates special
handling is added for x and sx gates since we can easily emit those
gates if appropriate when the x rotation angle aligns with using those
gates.

* Refactor mod 4pi and mod 2pi check to be more robust

Co-authored-by: Julien Gacon <gaconju@gmail.com>

* Add tests and handle phase correctly

This commit adds test coverage for the pass emitting X and SX gates. The
global phase handling for this was incorrect because it was not
correctly accounting for the phase difference between X/SX and RX. This
would lead to the phase being tracked incorrectly because for the
internal pass tracking it's all in terms of RX gates. So if the circuit
was in terms of RX gates added and we emitted an X we'd be off because
we didn't correct for the phase difference in the output circuit. This
was also a problem if the circuit was in terms of X gates and we emit an
X gate we had added the phase difference for the RX tracking but then we
emitted the X gate and didn't need the phase correction. To address this
we need to track the circuit gates and then on the output handle the
correction according to the gate we're emitting. This is different from
how Z angles are tracked because unlike the Z rotation gates, the other
options for X gates are only for discrete angles. We would need similar
handling if Z rotations could emit a Z gate but we don't support that
currently so it's not an issue.

* Add release note

* Avoid standalone tracking of gate counts

The previous commit that was correcting for the phase difference between
gates was relying on counting the X and SX gates used to compute the
angle and phase difference. This w... (continued)

Coverage Stats

35 of 35 new or added lines in 2 files covered. (100.0%)

27 existing lines in 4 files now uncovered.

109107 of 124720 relevant lines covered (87.48%)

961989.43 hits per line