Bug#225935: gcc-3.3: function static variable initialization allowed with pure functions only when -O is used
Britton <fsblk@aurora.uaf.edu> writes:
> > > Replaceing the strlen call with a call of an impure function
> > > (commented out above) results in the above error whether or not -O is
> > > used. It seems to me that pure function should either always be
> > > usable in this way regardless of -O (and C200? should endorse pure
> > > attribute and mandate the behavior), or never be supported.
> >
> > This has nothing to do with pureness; the standard mandates a constant
> > expression as initializer, and when optimizing, gcc replaces
> > "strlen(foo)" with 3. Correct handling of constant expressions in gcc
> > is mostly unimplemented, see http://gcc.gnu.org/PR456.
>
> It can only do that because it knows strlen is pure, thats the point
> of pureness.
That alone wouldn't suffice, the value has to be known at compile
time.
> If the standard says constant only, gcc should choke on strlen()
> with or without optimization.
Correct. Currently, it doesn't, which is what PR456 is about.
> > I suggest we either mark this as forwarded pointing to above bug, or
> > close it, since it is IMHO a pretty minor issue...
>
> I don't entirely understand that bug report, but I don't think it is the
> same since all the code in my example is evaluated.
I don't know what you mean by "evaluated".
> I don't agree that the bug is minor, it has already cost me several
> hours of confusion.
Well, it's an "accepts invalid", and it even does what you wanted...
> It lets you use the nice construct 'some_constant_string =
> "whatever"; static length_of_some_constant_string =
> strlen(some_constant_string);' instead of cutting and pasting the
> string constant only when optimization is on, which is confusing.
*shrug* it might be nice, but it's still invalid.
--
Falk
Reply to: