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Groups > muc.lists.netbsd.tech.toolchain > #3611

Re: netbsd-11 gcc bug

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> The reason for the "belief" that UB is (often) related to optimizers
> is squarely resting on the fact that when the optimizer is turned off
> then the UB goes away.

No, it doesn't.  It is still UB.  All that changes is what the compiler
chooses to do in that case where its behaviour is undefined by the
spec.

A more accurate phrasing would be that the compiler's choice of
behaviour changes depending on optimization.

The compiler must do *something* when faced with UB, whether it's
compiling code that does what the source author intended, segfaulting,
making usefulness-impairing inferences, or (in non-runtime cases)
printing all primes from 2 to 4294967291 at compile time.  UB just
means that the spec does not constrain what the compiler does.

> As I said, efforts to eliminate UB from C are actually happening at
> the standards committee level, so....

That will be difficult, unless some of them are handled by converting
UB to IDB by fiat.  Indirecting through a garbage pointer comes to mind
as an example.  (You're not going to get rid of garbage pointers
without crippling the language for use cases such as implementing VM
subsystems.)

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netbsd-11 gcc bug Manuel Bouyer <bouyer@antioche.eu.org> - 2026-05-23 10:59 +0200
  Re: netbsd-11 gcc bug Manuel Bouyer <bouyer@antioche.eu.org> - 2026-05-23 12:55 +0200
    Re: netbsd-11 gcc bug Manuel Bouyer <bouyer@antioche.eu.org> - 2026-05-23 20:45 +0200
  Re: netbsd-11 gcc bug Valery Ushakov <uwe@stderr.spb.ru> - 2026-05-23 14:22 +0300
    Re: netbsd-11 gcc bug Manuel Bouyer <bouyer@antioche.eu.org> - 2026-05-23 13:28 +0200
  Re: netbsd-11 gcc bug Roland Illig <roland.illig@gmx.de> - 2026-05-23 20:38 +0200
    Re: netbsd-11 gcc bug Manuel Bouyer <bouyer@antioche.eu.org> - 2026-05-23 20:47 +0200
      Re: netbsd-11 gcc bug Robert Elz <kre@munnari.OZ.AU> - 2026-05-24 02:29 +0700
        Re: netbsd-11 gcc bug Mouse <mouse@Rodents-Montreal.ORG> - 2026-05-23 19:11 -0400
          Re: netbsd-11 gcc bug Martin Husemann <martin@duskware.de> - 2026-05-24 10:44 +0200
            Re: netbsd-11 gcc bug Mouse <mouse@Rodents-Montreal.ORG> - 2026-05-24 08:33 -0400
              Re: netbsd-11 gcc bug Jason Thorpe <thorpej@me.com> - 2026-05-24 11:38 -0400
                Re: netbsd-11 gcc bug "Greg A. Woods" <woods@planix.ca> - 2026-05-24 16:53 -0700
              Re: netbsd-11 gcc bug David Holland <dholland-tech@netbsd.org> - 2026-05-25 00:02 +0000
                Re: netbsd-11 gcc bug Mouse <mouse@Rodents-Montreal.ORG> - 2026-05-25 08:23 -0400
                C compiler (over-)optimization (was: netbsd-11 gcc bug) Edgar Fuß <ef@math.uni-bonn.de> - 2026-05-29 19:12 +0200
                Re: C compiler (over-)optimization (was: netbsd-11 gcc bug) Mouse <mouse@Rodents-Montreal.ORG> - 2026-05-29 14:21 -0400
                Re: C compiler (over-)optimization (was: netbsd-11 gcc bug) "Greg A. Woods" <woods@planix.ca> - 2026-05-29 14:27 -0700
                Re: C compiler (over-)optimization Anders Magnusson <ragge@tethuvudet.se> - 2026-05-30 12:30 +0200
                Re: C compiler (over-)optimization (was: netbsd-11 gcc bug) Andrew Cagney <andrew.cagney@gmail.com> - 2026-05-31 13:02 -0400
                Re: C compiler (over-)optimization (was: netbsd-11 gcc bug) Jason Thorpe <thorpej@me.com> - 2026-05-31 14:29 -0500
                Re: netbsd-11 gcc bug "Greg A. Woods" <woods@planix.ca> - 2026-05-28 14:40 -0700
                Re: netbsd-11 gcc bug Mouse <mouse@Rodents-Montreal.ORG> - 2026-05-28 18:36 -0400
                Re: netbsd-11 gcc bug Jason Thorpe <thorpej@me.com> - 2026-05-28 19:04 -0400
                Re: netbsd-11 gcc bug "Greg A. Woods" <woods@planix.ca> - 2026-05-29 14:31 -0700
      Re: netbsd-11 gcc bug Jörg Sonnenberger <joerg@bec.de> - 2026-05-26 13:52 +0200
        Re: netbsd-11 gcc bug Jason Thorpe <thorpej@me.com> - 2026-05-26 10:02 -0400

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