Issue with LTO/-fwhole-program

[Joseph S. Myers]

On Sun, 13 Jun 2010, Dave Korn wrote:

> On 13/06/2010 20:55, Ian Lance Taylor wrote:
> > David Brown <david@westcontrol.com> writes:
> > 
> >> If -flto were to activate the -fno-common flag, would that then catch 
> >> these potential problems with a linker error?
> > 
> > We could perhaps do that for C/C++ code, but Fortran relies on common 
> > symbols.
> 
> Well we shouldn't do it for plain C either, or at the very least should make
> it depend on the -std= option in effect, but since the code is entirely valid
> and legitimate C, I think we should acknowledge this is a weakness in our
> compiler. The original testcase is a perfectly straightforward bit of C89;
> there are two compatible tentative declarations of a variable of type int
> called "v". We don't want to have to argue that one is in fact a variable of

This is not valid standard C; you can have two tentative definitions in 
the same translation unit, but not in different translation units.  
Allowing commons is listed as a common extension in C90 G.5.11.

-- 
Joseph S. Myers
joseph@codesourcery.com