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04:38:39 <esolangs> [[Talk:Footsteps]] https://esolangs.org/w/index.php?diff=106838&oldid=105580 * Ais523 * (+615) /* Start 0 */ reply to [[User:Salpynx]]
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08:18:06 <esolangs> [[User:Orisphera/Completeness]] https://esolangs.org/w/index.php?diff=106839&oldid=106822 * Orisphera * (+39) /* What is a programming language? */
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15:40:40 <int-e> TIL that unproductive endless loops like `for (;;) {}` are UB in C++ :-/
15:43:35 <FireFly> in general? I know that having main diverge is UB in C++ but I thought it might be specific to main somehow
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15:46:00 <int-e> FireFly: https://en.cppreference.com/w/cpp/language/memory_model includes a "progress guarantee" and LLVM has started to take advantage of it, leading to https://karlsruhe-social.de/system/cache/media_attachments/files/109/856/328/357/566/082/original/abdcd25332d18d5a.png (confirmed with versions 13.x and 14.x)
15:47:44 <int-e> (seen on ##rust-offtopic)
15:54:09 <FireFly> *nod*
15:59:42 <fizzie> There's a similar C thing (since C11) but it's restricted to loops that have a non-constant controlling expression.
16:01:32 <fizzie> C11 6.8.5p6: "An iteration statement whose controlling expression is not a constant expression, that performs no input/output operations, does not access volatile objects, and performs no synchronization or atomic operations in its body, controlling expression, or (in the case of a `for` statement) its /expression-3/, may be assumed by the implementation to terminate."
16:01:54 <fizzie> Inherited from one of those C <-> C++ harmonization efforts, I believe.
16:02:32 <fizzie> https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1349.htm "Non-terminating loops"
16:03:51 <fizzie> AIUI the "-- controlling expression is not a constant expression --" part was added in committee deliberations because of the body of existing C code that used `for (;;);` as a "should not be reached, and execution should not continue if reached" construct.
16:07:35 <esolangs> [[Special:Log/newusers]] create * Vodracseck * New user account
16:12:05 <esolangs> [[Esolang:Introduce yourself]] https://esolangs.org/w/index.php?diff=106840&oldid=106825 * Vodracseck * (+74) /* Introductions */
16:19:28 <b_jonas> int-e: ok, that does look weird. I'd not be surprised if the while(1); loop could end in finite time, since that's a look with no side effects so it can be optimized away to nothing. but I don't see how you'd enter the other function. it can't be UB caused by the missing return statement in main because this is C++ code, not C, and C++ has an implicit return 0 at the end of main.
16:24:05 <b_jonas> are you saying that the while(1); loop can be optimized to unreachable somehow instead of just optimized to a nop?
16:27:02 <FireFly> how would the loop ned in finite time?
16:27:04 <FireFly> end*
16:28:33 <b_jonas> FireFly: it can't really, but since it never causes side effects and never changes any value that can be observed from the outside, I assume the compiler can optimize it as if it ended in finite time and did nothign
16:28:40 <b_jonas> I don't think it can optimize it to UB
16:31:11 <b_jonas> but no, I can't cite the standard for this
16:31:18 <b_jonas> it's just how I think it might work
16:31:50 <b_jonas> but maybe that's not right
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16:32:04 <b_jonas> yeah, it shouldn't be optimized to a nop
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16:33:03 <FireFly> I've heard the thing about divergence being explicitly UB, and I think a compiler replacing an infinite loop without side-effect with a nop def woludn't be fine (well uh, I guess it would be as a consequence when it's UB, but like, just indirectly in that it could do anything)
16:33:13 <FireFly> but I don't really speak C++ much
16:33:26 <b_jonas> imagine a loop that searches for a counterexample to the Goldbach conjecture (or a contradiction in ZF or whatever), and then the statement after the loop just prints "found" without printing any more specific info about the loop. presumably you don't want that loop to be optimized away to nop, so this infinite loop shouldn't be either
16:34:29 <b_jonas> (of course that loop might be hard to write in a way that the compiler can prove it has no side-effect, since a naive implementation will have malloc call sbrk or mmap, but that's just a technical problem, the compiler can know enough about malloc to know that those aren't real side effects)
16:35:52 <b_jonas> (I think both C++ and rust folks are working on that you can eventually heap-allocate from compile-time code)
16:36:41 <b_jonas> (and besides, you can just avoid the malloc by searching for a counterexample that fits a gigabyte of pre-allocated memory, presumably the compiler won't be smart enough to be able to prove that that doesn't terminate)
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22:02:27 <esolangs> [[Abc!?]] https://esolangs.org/w/index.php?diff=106841&oldid=100412 * 1hals * (+2371) Clarify variables and operation types
22:05:11 <esolangs> [[Abc!?]] https://esolangs.org/w/index.php?diff=106842&oldid=106841 * 1hals * (+85) /* Move statement */
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22:09:48 <esolangs> [[Abc!?]] https://esolangs.org/w/index.php?diff=106843&oldid=106842 * 1hals * (+316) re-organize the operators section
22:10:38 <esolangs> [[Abc!?]] https://esolangs.org/w/index.php?diff=106844&oldid=106843 * 1hals * (-293) remove the redundant special features section
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22:31:55 <esolangs> [[Abc!?]] https://esolangs.org/w/index.php?diff=106845&oldid=106844 * 1hals * (+598) Add untested Fibonacci example
22:34:20 <esolangs> [[Abc!?]] https://esolangs.org/w/index.php?diff=106846&oldid=106845 * 1hals * (+210)
22:38:29 <esolangs> [[Abc!?]] M https://esolangs.org/w/index.php?diff=106847&oldid=106846 * 1hals * (+24) /* Variables */
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23:21:10 <int-e> b_jonas: the crazy thing is that it discards the code *after* the loop as unreachable, but also discards the loop.
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