[llvm] r176341 - GCC thinks that this variable might be used uninitialized (it isn't).

[Arnaud de Grandmaison]

On Thursday 21 March 2013 18:19:14 Duncan Sands wrote:
> I looked into this a bit more, and the problem occurs when using cmake not
> when using configure+make.  The problem is that cmake puts
> -Wno-maybe-uninitialized before -Wall while configure+make has them the
> other way round.  I'm not sure how to fix this, not knowing anything about
> cmake.
> 

In file "modules/HandleLLVMOptions.cmake", line 189 looks weird to me:

add_llvm_definitions( -Wall -W -Wno-unused-parameter -Wwrite-strings )

The add_definition (called inside the upper wrapper) is normally used fo
" -DVAR=blabla" things.

You would have rather expected the append_if(CMAKE_CXX_FLAGS... or 
append_if(CMAKE_C_FLAGS... to be used to setup the warning filters.

Cheers,
--
Arnaud

> Ciao, Duncan.
> 
> PS: I'm using cmake+ninja.
> 
> On 01/03/13 18:01, Michael Liao wrote:
> > On Fri, 2013-03-01 at 02:50 -0800, Chandler Carruth wrote:
> >> On Fri, Mar 1, 2013 at 1:46 AM, Duncan Sands <baldrick at free.fr> wrote:
> >>          GCC thinks that this variable might be used uninitialized (it
> >>          isn't).
> >> 
> >> Sorry to keep kicking the horse here, but I really oppose adding dead
> >> stores to silence a broken warning.
> >> 
> >> 
> >> We'll no longer be able to use Valgrind to catch a bug where the
> >> control flow that intends to initialize this variable suddenly changes
> >> and fails to do so in one case. =[ That seems really bad.
> >> 
> >> 
> >> Clang's warnings don't have this false positive, and there is even a
> >> way to silence GCCs in modern GCCs (-Wno-maybe-uninitialized) because
> >> of this problem. Can we just turn off old GCC -Wuninitialized and rely
> >> on the modern compilers' warnings instead?
> > 
> > shall we add that option by default in our makefile*?
> > 
> > - michael
> > 
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