functions bodies ending in infinite loops execute false branches

[Artyom Bologov]

I'm doing a CLI app that starts some threads and then does (loop) to force the executable stay alive and not (quit). However, having:
- function body ending in (loop) or equivalent infinite loop (I've tried (loop while t) and (loop for i = 0 until (plusp i)), for instance),
- (if arg ...) or (when arg ...) checks in the body,
- and some non-obviously-nil arg
makes the if/when before the (loop) to execute unconditionally, even if the condition is false.

The code snippet that shows the behavior reliably:
(progn
  (defvar *whatever-var* nil)
  (defun whatever ()
    (let ((arg (parse-integer
                ""
                :junk-allowed t)))
      (when arg
        (setf *whatever-var* "woo")))
    (loop))
  (sb-thread:make-thread (lambda ()
                    (whatever)))
  (sleep 1)
  *whatever-var*)

2. SBCL version:
$ sbcl --version
SBCL 2.2.6

3. uname output
$ uname -a
Linux paranoidal 5.18.10 #1 SMP PREEMPT_DYNAMIC 1 x86_64 GNU/Linux

4. Features
CL-USER> *features*
(:SLYNK CFFI-FEATURES:FLAT-NAMESPACE CFFI-FEATURES:X86-64 CFFI-FEATURES:UNIX
 :CFFI CFFI-SYS::FLAT-NAMESPACE ALEXANDRIA::SEQUENCE-EMPTYP :QUICKLISP :ASDF3.3
 :ASDF3.2 :ASDF3.1 :ASDF3 :ASDF2 :ASDF :OS-UNIX :NON-BASE-CHARS-EXIST-P
 :ASDF-UNICODE :X86-64 :GENCGC :64-BIT :ANSI-CL :COMMON-LISP :ELF
 :IEEE-FLOATING-POINT :LINUX :LITTLE-ENDIAN :PACKAGE-LOCAL-NICKNAMES
 :SB-CORE-COMPRESSION :SB-LDB :SB-PACKAGE-LOCKS :SB-THREAD :SB-UNICODE :SBCL
 :UNIX)

[Stas Boukarev (stassats)]

I hope you don't actually have a (loop) in your code. That just wastes enormous amounts of CPU time.