[Bug c/68065] Size calculations for VLAs can overflow

[joseph at codesourcery dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68065

--- Comment #8 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
I think it's undefined at the point where a type exceeds the limit on the 
size of an object (half the address space minus one byte), whether or not 
sizeof is used or any object with that type is constructed - that is, as 
soon as the language semantics involve evaluation of the array sizes for 
the VLA type in question.  (If the sizes are neither evaluated nor 
required, e.g. sizeof (int (*)[size]), or when replaced by [*] at function 
prototype scope, I don't consider that undefined; if required but not 
evaluated, as in certain obscure cases of conditional expressions, that's 
a different case of undefined behavior.)