[Bug c/65892] gcc fails to implement N685 aliasing of union members

[joseph at codesourcery dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65892

--- Comment #19 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
On Tue, 1 Nov 2016, txr at alumni dot caltech.edu wrote:

> Five:  The answer to the question is clearly No.  The example code
> is very much on point to the "one special guarantee" clause, and
> so the read access p1->m is permitted.  As the access is permitted,

I maintain that, as I said in comment#9, the textual history indicates 
that the original intent of saying things are permitted here is *only* an 
exception to the general implementation-defined nature of type punning, 
not to any other reason why things might be undefined (such as aliasing 
rules, data races, etc.).