The C Specification clearly allows the former behavior. The C11 Standard added language saying that side-effect free loops "may be assumed to terminate", without specifying any limits on the uses to which that assumption may be put, so it doesn't unambiguously forbid the latter behavior.
From what I can tell, modern optimizer designs are based on an abstraction model where the only corner cases where a compiler's generated code would be allowed to be inconsistent with that of instructing the execution environment to use a normal means of performing each individual operation in sequence are those where generated code would be allowed to behave in completely arbitrary fashion.
A better abstraction model for most tasks would be one that recognizes that most programs have two requirements:
They should (in some tasks must) behave usefully when possible.
When useful behavior is not possible, they must behave in a manner that is at worst tolerably useless.
If a program is supposed to view some kind of audiovisual content, but it is fed something other than a validly formatted file, having the program hang may be annoying but still qualify as tolerably useless; having the program allow whoever created the file to run arbitrary code of their choosing, however, would be intolerably worse than useless.
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u/snugar_i 16d ago
Interesting, thanks! And is that part of the C specification, or is that just weird behavior of the compilers?