  Polar codes are linear block codes that can achieve channel capacity at
infinite code length. Successive cancellation list (SCL) decoding relies on a
set of parallel decoders; it yields good error-correction performance at finite
code length, at the cost of increased implementation complexity and power
consumption. Current efforts in literature focus on design-time decoder
complexity reduction, while lacking practical run-time power reduction methods.
In this work, input-distribution-aware SCL (IDA-SCL) decoding is proposed, that
allows to determine the parallelism to adopt by performing simple observations
on the input of the decoder. This technique guarantees fixed, short latency and
allows hardware SCL decoders to dynamically shut down part of the internal
parallelism before each decoding process. It can be combined with existing
complexity- and power- reduction techniques. Simulation results show that
IDA-SCL can reduce the run-time complexity of SCL of up to 50\%.
