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From: James Kuyper <jameskuyper@alumni.caltech.edu>
Newsgroups: comp.lang.c,comp.lang.c++
Subject: Re: Compile time checking of standards conformance
Date: Thu, 23 May 2024 14:13:26 -0400
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On 5/23/24 02:23, Paavo Helde wrote:
....
> There are zillions of ways to write non-conforming code, for example an 
> endless loop is not conforming in C++.

Citation, please? How does it fail to conform?

> ... The compiler is not obliged to 
> diagnose it, but it is allowed for the compiler to silently optimize the 
> non-conforming code away, assuming it is never called. At least that's 
> what g++ folks think.

The C standard contains the following wording:

"An iteration statement may be assumed by the implementation to
terminate if its controlling expression is not a constant expression200)
, and none of the following operations are performed in its body,
controlling expression or (in the case of a for statement)
itsfexpression-3201) :
— input/output operations
— accessing a volatile object
— synchronization or atomic operations."

In essence, those restrictions mean that the body of the loop does
nothing that need take up any time, so it can be optimized to a nop.
Infinitely many repetitions times 0 execution time has a product that is
mathematically meaningless, but the C standard permits optimizing to
terminate after a finite amount of time.

Note that this does not apply to endless loops occurring by other means,
such as goto.

The optimization you describe would therefore be permitted for C if
those conditions are met - but I can find no corresponding language in
the latest draft I have of the C++ standard (n4928.pdf, dated
2022-12-18). It's a big standard - I might have missed something.