failed AVER: (EQ (SB-C::IR2-LVAR-KIND SB-C::2LVAR) :UNKNOWN)

[Paul F. Dietz]

(lambda ()
  (let ((x (ignore-errors (funcall #'list 0))))
    (declare (dynamic-extent x))
    x))

==>

failed AVER: (EQ (SB-C::IR2-LVAR-KIND SB-C::2LVAR) :UNKNOWN)
This is probably a bug in SBCL itself. (Alternatively, SBCL
might have been corrupted by bad user code, e.g. by an undefined
Lisp operation like (FMAKUNBOUND 'COMPILE), or by stray pointers
from alien code or from unsafe Lisp code; or there might be a
bug in the OS or hardware that SBCL is running on.) If it seems
to be a bug in SBCL itself, the maintainers would like to know
about it. Bug reports are welcome on the SBCL mailing lists,
which you can find at <http://sbcl.sourceforge.net/>.
   [Condition of type SB-INT:BUG]

Restarts:
 0: [RETRY] Retry SLIME REPL evaluation request.
 1: [*ABORT] Return to SLIME's top level.
 2: [ABORT] abort thread (#<THREAD tid=31593 "repl-thread" RUNNING {10011F0003}>)

Backtrace:
  0: (SB-C::%NIP-VALUES-IR2-CONVERT-OPTIMIZER #<SB-C::COMBINATION :FUN #<SB-C::REF :LEAF #<SB-C::GLOBAL-VAR :%SOURCE-NAME SB-C::%NIP-VALUES :TYPE #1=#<SB-KERNEL:FUN-TYPE #> :DEFINED-TYPE #1# :WHERE-FROM :..
  1: (SB-C::IR2-CONVERT-BLOCK #<SB-C::CBLOCK 3 :START c1 {100F7584D3}>)
  2: (SB-C:IR2-CONVERT #<SB-C:COMPONENT :NAME "<unknown>" {100F7473E3}>)
  3: (SB-C::%COMPILE-COMPONENT #<SB-C:COMPONENT :NAME "<unknown>" {100F7473E3}>)
  4: (SB-C::COMPILE-COMPONENT #<SB-C:COMPONENT :NAME "<unknown>" {100F7473E3}>)
  5: (SB-C::%COMPILE (LAMBDA NIL (LET (#) (DECLARE #) X)) NIL NIL)
[...]

x86-64, "2.3.11.167-1ba132815"

This is not valid code (the freshly consed list is in a dynamic-extent variable, but is returned), but it should not cause a compiler error.