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Re: [Patch to gcc/function] PR 58362

On Mon, Sep 09, 2013 at 11:37:31AM +0200, Richard Biener wrote:
> > > > > this patchlet fixes the column # of the unused parameter warnings emitted
> > > > > by
> > > > > do_warn_unused_parameter by explicitly passing DECL_SOURCE_LOCATION (decl)
> > > > > instead of wrongly relying on '+', which in this case ends up meaning the
> > > > > location of the function declaration. Tested x86_64-linux.
> > > > I would have expected %q+D to use the location of the corresponding
> > > > decl, not some random other location.  So, isn't the bug in the
> > > > C++ frontend diagnostic machinery?
> > > Well, first notice that the patch fixes the issue *both* for the C and C++
> > > front-ends, that's why I added the testcase to c-c++-common. This isn't a C++
> > > issue. Then notice that we do already have tens of cases where we use
> > > DECL_SOURCE_LOCATION + %qD, when we want to be precise about the location. The
> > > diagnostic machinery has this mechanism using + which uses location_of, which
> > > is often useful for expressions, but which very often we don't use for decls.
> > > In fact, some people, like Manuel, see the audit trail of the bug, find the
> > > mechanism quite confusing. Is there something specific you want me to check?
> > 
> > How is '+' in %q+D defined?  I failed to find documentation of the
> > diagnostic formats (but only searched for like two minutes).
> That said, grepping for %q+D reveals quite some uses and it looks like
> all of them expect the location being used to be that of the decl passed
> to the diagnostic call, not some random other location.

The C++ FE locus handling is in very bad shape (C FE is much better, Aldy
and others have spent quite some time fixing all the issues).  I guess this
is just one of the many issues.  The most annoying to me is that the C++ FE
for function calls uses the location of the closing ) of the call expression
rather than the function name or at least opening (, so if you have a 
  call_something (one_arg,
you really don't see what is being called in the debugger when debugging


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