[cfe-dev] Build Errors

[David Blaikie]

On Wed, Feb 29, 2012 at 1:22 PM, Chandler Carruth <chandlerc at google.com> wrote:
> I really would like to avoid silencing the GCC "may be used uninitialized"
> warnings by introducing unnecessary initialization.
>
> These warnings are almost always false positives due to the way the warning
> was implemented. What it means is that GCC has been unable to *prove*
> initialization took place, and has not hit one of a (very short) list of
> known impossible cases. This warning was bad enough that we (Google) lobbied
> upstream and I believe it is now under a separate flag from -Wuninitialized.
>
> Every time we add initializations like this we achieve three things:
>
> 1) placate a fundamentally flawed warning
> 2) slow down code in some cases (the ability to eliminate the initialization
> corresponds to when this warning *doesn't* fire)
> 3) prevent us from ever getting Valgrind errors if we in fact introduce a
> bug leaving the variable uninitialized.
>
> It is #3 that makes me really bothered by the spirit of these changes. I
> would like to recommend anyone using an older GCCs should simply disable
> -Wuninitialized.

Should we add some handling for this in the LLVM build if that's the
case/achievable/sufficiently useful?

- David

> We will catch all of the bugs with Clang's -Wuninitialized
> and Valgrind.
>
> On Wed, Feb 29, 2012 at 1:16 PM, Chad Rosier <mcrosier at apple.com> wrote:
>>
>> Eli took care of this in r151754.
>>
>>  Chad
>>
>> On Feb 29, 2012, at 12:54 PM, David Greene wrote:
>>
>> > I get the follwing build errors with -Werror:
>> >
>> > [sta-opt]    : [llvm]
>> > /ptmp/dag/llvm/staging/llvm/tools/clang/lib/AST/Expr.cpp: In static member
>> > function 'static int clang::StringLiteral::mapCharByteWidth(const
>> > clang::TargetInfo&, clang::StringLiteral::StringKind)':
>> > [sta-opt]    : [llvm]
>> > /ptmp/dag/llvm/staging/llvm/tools/clang/lib/AST/Expr.cpp:518:80: error:
>> > 'CharByteWidth' may be used uninitialized in this function
>> > [-Werror=uninitialized]
>> > [sta-opt]    : [llvm] cc1plus: all warnings being treated as errors
>> >
>> > Can someone fix this?  I don't have commit access.
>> >
>> > Thanks!
>> >
>> >                             -Dave
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