`fptr01` fails in the `sanity` way
fptr01 test fails when sanity-checking is enabled due to an assertion failure:
h33 g33 f33 f_env 3 35 f_env 2 35 f_env 1 35 fptr01: internal error: ASSERTION FAILED: file rts/sm/Sanity.c, line 333 (GHC version 9.1.20210103 for x86_64_unknown_linux) Please report this as a GHC bug: https://www.haskell.org/ghc/reportabug Aborted
The cause is quite straightforward: the weak pointer list check in
checkGenWeakPtrList (added by b1d2c1f3) failed to account for the fact that weak pointers may have
DEAD_WEAK closure type.