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Re: Issue with LTO/-fwhole-program


On 13/06/2010 23:20, Joseph S. Myers wrote:
> 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; 

  Not valid *which 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.

  So your objection is that it *is* valid after all?  I'm not following.  As
far as I remember that sort of thing, ropey though it seems nowadays, was
always an accepted part of K'n'R C, which I thought was what C89 aimed to
formalize.

    cheers,
      DaveK


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