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Speed up circuit construction when contents are a list of moments #5898

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Sep 29, 2022
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Speed up circuit construction when contents are a list of moments #5898

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ef0e9be
Speed up circuit construction when contents are a list of moments
tanujkhattar Sep 28, 2022
4b223a0
Add explicit cast to fix mypy errors
tanujkhattar Sep 29, 2022
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8 changes: 6 additions & 2 deletions cirq-core/cirq/circuits/circuit.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1741,11 +1741,15 @@ def __init__(
circuit.
"""
self._moments: List['cirq.Moment'] = []
flattened_contents = tuple(ops.flatten_to_ops_or_moments(contents))
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I'd probably go for list instead, since we don't need immutability here, but it'd be interesting to know if there is any performance difference one way or the other. If not, then up to you whether to use list or tuple.

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Tuples are usually slightly faster than lists because they don't overallocate like lists (to make append faster) so the memory footprint is more compact. Also, tuples don't need to go through an additional level of indirection when accessing elements like lists; see https://stackoverflow.com/a/22140115 for more details

As an example, here are numbers for running the operation by operation construction benchmark (in which the flattened_contents would contain all the operations and hence have a large size).

Using tuples for flattened_contents:

[  0.00%] ·· Benchmarking existing-py_usr_local_google_home_tanujkhattar_anaconda3_envs_cirq_bin_python
[ 50.00%] ··· Running (circuit_construction.SurfaceCodeRotatedMemoryZ.time_circuit_construction_operations_by_operation--).    
[100.00%] ··· circuit_construction.SurfaceCodeRotatedMemoryZ.time_circuit_construction_operations_by_operation                                                                                                                                                                          ok
[100.00%] ··· ========== ============
               distance              
              ---------- ------------
                  3       2.68±0.1ms 
                  5       18.2±0.7ms 
                  7        72.2±2ms  
                  9        198±6ms   
                  11       464±10ms  
                  13       933±40ms  
                  15      1.68±0.06s 
                  17      2.95±0.09s 
                  19      4.73±0.2s  
                  21      6.39±0.02s 
                  23      9.50±0.03s 
                  25      13.7±0.4s  
              ========== ============

Using lists for flattened_contents:

[  0.00%] ·· Benchmarking existing-py_usr_local_google_home_tanujkhattar_anaconda3_envs_cirq_bin_python
[ 50.00%] ··· Running (circuit_construction.SurfaceCodeRotatedMemoryZ.time_circuit_construction_operations_by_operation--).
[100.00%] ··· circuit_construction.SurfaceCodeRotatedMemoryZ.time_circuit_construction_operations_by_operation                                                                                                                                                                          ok
[100.00%] ··· ========== ============
               distance              
              ---------- ------------
                  3       2.81±0.2ms 
                  5       20.3±0.8ms 
                  7        79.9±3ms  
                  9        204±4ms   
                  11       467±10ms  
                  13       934±10ms  
                  15      1.75±0.1s  
                  17      2.92±0.08s 
                  19      4.42±0.1s  
                  21      6.65±0.02s 
                  23      9.85±0.04s 
                  25      13.8±0.2s  
              ========== ============

if all(isinstance(c, Moment) for c in flattened_contents):
self._moments[:] = cast(Iterable[Moment], flattened_contents)
return
with _compat.block_overlapping_deprecation('.*'):
if strategy == InsertStrategy.EARLIEST:
self._load_contents_with_earliest_strategy(contents)
self._load_contents_with_earliest_strategy(flattened_contents)
else:
self.append(contents, strategy=strategy)
self.append(flattened_contents, strategy=strategy)

@classmethod
def _from_moments(cls, moments: Iterable['cirq.Moment']) -> 'Circuit':
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