> type1 *foo(const type1 *my_const_ptr)
> {
> union {
> type1 *t1;
> const type1 *ct1;
> } v;
> v.ct1 = my_const_ptr;
> return v.t1;
> }
Yes, that is sad, and it seems like just a matter of time before a C++
compiler looks at the code above and reasons that the write to ct1 can be
optimized away because there is no code that ever reads from ct1. Thus the
read from t1 will be recognized as undefined behavior (probably called a
poison value in LLVM) and anything could happen.
What was the problem with Mateusz's patch? I think people are implying it
results in compiler warnings, but I thought casting a pointer to a pointer
usually doesn't give any warnings.
--David
On Fri, Apr 7, 2017 at 4:33 AM, Norbert Pfeiler <
[email protected]> wrote:
> That’s a kinda sad stance for a compiler support project, don’t you think?
>
> Best, Norbert.
>
> Liu Hao <[email protected]> schrieb am Fr., 7. Apr. 2017 um 05:48 Uhr:
>
> > On 2017/4/7 8:11, Norbert Pfeiler wrote:
> > > Wasn’t LH_Mouse’s point that even if the warning is explicitly turned
> on
> > it
> > > wouldn’t be shown to the user?
> > >
> > > The situation for unions is different in C and C++: (I don’t think that
> > > it’s just about constness changes anything)
> > > http://stackoverflow.com/questions/11373203
> > Nice link. Nevertheless, I don't think most people care about UB unless
> > UB bites them (that is, unless UB refuses to work silently). XD
> >
> > --
> > Best regards,
> > LH_Mouse
> >
> >
> >
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