  This paper has been prepared by the HEP Software Foundation (HSF) Physics
Event Generator Working Group (WG), as an input to the second phase of the LHCC
review of High-Luminosity LHC (HL-LHC) computing, which is due to take place in
November 2021. It complements previous documents prepared by the WG in the
context of the first phase of the LHCC review in 2020, including in particular
the WG paper on the specific challenges in Monte Carlo event generator software
for HL-LHC, which has since been updated and published, and which we are also
submitting to the November 2021 review as an integral part of our contribution.
