[libcxx] r176640 - Albert Wong: definition for regex_traits<_CharT>::__regex_word.

[Albert Wong (王重傑)]

On Thu, Mar 7, 2013 at 12:40 PM, David Blaikie <dblaikie at gmail.com> wrote:

> On Thu, Mar 7, 2013 at 12:31 PM, Albert Wong (王重傑) <ajwong at google.com>
> wrote:
> > My understanding was that static data members needed to be defined, even
> if
> > they are integral types that are initialized with a constant expression
> with
> > an exception being made if they are not "odr-used."  (See
> > [class.static.data]p3)
> >
> > I don't 100% understand odr-used but I think __regex_word's usage in a
> > non-const expression at line 1205 means this it needs to be defined and
> not
> > just declared.
>
> In C++98 this is probably true (were you compiling in C++98 mode?). In
> C++11 I don't believe this is true.
>
> "A variable whose name appears as a potentially-evaluated expression
> is odr-used unless it is an
> object that satisfies the requirements for appearing in a constant
> expression (5.19) and the lvalue-to-rvalue
> conversion (4.1) is immediately applied"
>
> (what this basically means, as I understand it, is: so long as you
> don't need the "object" (eg: you don't take its address/want to point
> to it at any time) just the value, you don't need to provide
> definitions for constants)
>

Sounds sensible. Then I'm guessing gcc must be doing something silly. I was
indeed building --std=c++11.

 > As for making a test for this...it'd probably be difficult to write one
> that
> > was guaranteed to fail.  In the specific failure that prompted this, the
> > MIPS g++ somehow ended up with an unresolved symbol.  Oddly enough, the
> ARM
> > and x86 variants of the same compiler version didn't do this.
>
> Do you have a MIPS bot or could contribute one? Some way to avoid
> regressing things like this would be helpful for yourself & the
> community.
>

Sadly, no.  I'm only 20% on the project to make libcxx work on Android
(normally a Chrome dev) so I don't really have much knowledge about their
builders, etc.  Also, until libcxx actually works on the Android toolchain,
I doubt if such a bot would ever stay green.

-Albert



> >
> > -Albert
> >
> >
> >
> > On Thu, Mar 7, 2013 at 11:56 AM, Howard Hinnant <hhinnant at apple.com>
> wrote:
> >>
> >> I don't have one.  In order for me to detect this I would have to take
> the
> >> address of __regex_word, and to the best I've been able to tell, on
> Apple
> >> platforms libc++ never does this.  However Albert Wong reported errors
> on
> >> MIPS Android which this addition fixed.  I did run the regex tests on
> OS X
> >> before and after this addition and they all passed.  I view this
> addition as
> >> benign on Apple platforms, and happy to help out on MIPS Android.
> >>
> >> Howard
> >>
> >> On Mar 7, 2013, at 2:47 PM, David Blaikie <dblaikie at gmail.com> wrote:
> >>
> >> > Is there a test case to go with this?
> >> >
> >> > On Thu, Mar 7, 2013 at 11:38 AM, Howard Hinnant <hhinnant at apple.com>
> >> > wrote:
> >> >> Author: hhinnant
> >> >> Date: Thu Mar  7 13:38:08 2013
> >> >> New Revision: 176640
> >> >>
> >> >> URL: http://llvm.org/viewvc/llvm-project?rev=176640&view=rev
> >> >> Log:
> >> >> Albert Wong: definition for regex_traits<_CharT>::__regex_word.
> >> >>
> >> >> Modified:
> >> >>   libcxx/trunk/include/regex
> >> >>
> >> >> Modified: libcxx/trunk/include/regex
> >> >> URL:
> >> >>
> http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/regex?rev=176640&r1=176639&r2=176640&view=diff
> >> >>
> >> >>
> ==============================================================================
> >> >> --- libcxx/trunk/include/regex (original)
> >> >> +++ libcxx/trunk/include/regex Thu Mar  7 13:38:08 2013
> >> >> @@ -1009,6 +1009,10 @@ private:
> >> >> };
> >> >>
> >> >> template <class _CharT>
> >> >> +const typename regex_traits<_CharT>::char_class_type
> >> >> +regex_traits<_CharT>::__regex_word;
> >> >> +
> >> >> +template <class _CharT>
> >> >> regex_traits<_CharT>::regex_traits()
> >> >> {
> >> >>    __init();
> >> >>
> >> >>
> >> >> _______________________________________________
> >> >> cfe-commits mailing list
> >> >> cfe-commits at cs.uiuc.edu
> >> >> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
> >>
> >
>
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