`SIGSEGV` regression from Nim v2.2.4 to v2.2.6/devel with closure iteratures

[tersec]

Nim Version

No SIGSEGV:

Nim Compiler Version 2.2.4 [Linux: amd64]
Compiled at 2025-11-03
Copyright (c) 2006-2025 by Andreas Rumpf

git hash: f7145dd26efeeeb6eeae6fff649db244d81b212d
active boot switches: -d:release

SIGSEGV:

Nim Compiler Version 2.2.6 [Linux: amd64]
Compiled at 2025-11-05
Copyright (c) 2006-2025 by Andreas Rumpf

git hash: ab00c56904e3126ad826bb520d243513a139436a
active boot switches: -d:release

Nim Compiler Version 2.3.1 [Linux: amd64]
Compiled at 2025-11-05
Copyright (c) 2006-2025 by Andreas Rumpf

git hash: cfefd1d95b02fe8c099ee28074616031cf5a0b3b
active boot switches: -d:release

Description

iterator y(): int {.closure.} =
  try:
    try:
      raise newException(CatchableError, "")
    except CatchableError:
      return
    yield 0
  finally:
    discard

let w = y
discard w()

Current Output

/tmp/m.nim(7, 5) Warning: unreachable code after 'return' statement or '{.noReturn.}' proc [UnreachableCode]
CC: system/exceptions.nim
CC: std/private/digitsutils.nim
CC: system/dollars.nim
CC: system.nim
CC: m.nim
Hint:  [Link]
Hint: mm: orc; threads: on; opt: none (DEBUG BUILD, `-d:release` generates faster code)
28942 lines; 0.491s; 31.199MiB peakmem; proj: /tmp/m.nim; out: /tmp/m [SuccessX]
Hint: /tmp/m [Exec]
Traceback (most recent call last)
/tmp/m.nim(12)           m
/tmp/m.nim(1)            y
SIGSEGV: Illegal storage access. (Attempt to read from nil?)
Segmentation fault
Error: execution of an external program failed: '/tmp/m'

Expected Output

No SIGSEGV

Known Workarounds

No response

Additional Information

No response

[tersec]

Potentially more idiomatic-looking code apparently triggering the same issue (though, neither should SIGSEGV):

iterator y(): int {.closure.} =
  try:
    try:
      raise newException(CatchableError, "")
    except CatchableError:
      return
    yield 0
  finally:
    discard
for _ in y(): discard

[narimiran]

Git bisect points at: #25244

cc @yglukhov