unsafeCoerce of data constructor application results in invalid code generation

@RyanGlScott noticed that a program using his parameterized-utils library crashes reliably in all GHC versions from 8.6 to 9.0.1 and helpfully produced a minimal reproducer ($2777). Specifically compiling and running this program under -O0 results in a runtime error:

hi: internal error: stg_ap_pp_ret
    (GHC version 9.0.1 for x86_64_unknown_linux)
    Please report this as a GHC bug:  https://www.haskell.org/ghc/reportabug
Aborted (core dumped)

Running with -O2 prints an different result depending upon which GHC version is used.

Edited May 19, 2021 by Ben Gamari

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