[cfe-dev] Undiagnosed "reference to stack memory [...] returned"

[Argyrios Kyrtzidis]

Hi Matthieu,

Sorry for the (very..) late response. We now warn for all cases since
http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20101129/036838.html

Thanks for reporting the issue!

-Argiris

On Wed, Sep 15, 2010 at 11:04 AM, Matthieu Monrocq <
matthieu.monrocq at gmail.com> wrote:

> Hi guys,
>
> here is a very simple test case:
>
>     int const& get_reference_warning()
>     {
>       int w = 0;
>       return w; // expected-warning{{reference to stack memory associated
> with local variable 'w' returned}}
>     }
>
>     int get_value();
>
>     int const& get_reference_no_warning() { return get_value(); } //
> Diagnosed by VC++ 2010 (haven't tested on gcc), but unnoticed by Clang
>
>     int const& get_reference_no_warning_2()
>     {
>       int const& w2 = get_value();         // Correct, lifetime of the
> value is extended to the lifetime of the const reference
>       return w2;                                   // Undefined behavior:
> goes unnoticed by Clang, VC++ 2010 and gcc 3.4.2
>     }
>
> I compiled it with:   clang.exe -fsyntax-only -Wall -pedantic test.cpp
> (on Windows, using PowerShell)
>
>     test.cpp(9) :  warning: reference to stack memory associated with local
> variable 'w' returned
>       return w; // expected-warning{{reference to stack memory associated
> with local variable 'w' returned}}
>          ^
>     1 warning generated.
>
> As expected, the first return provoked a warning.
>
> However in the two other cases, no warning is generated.
>
> I was wondering if it would be possible for clang to diagnose those cases
> as well. I guess the third case is the trickier, though since the lifetime
> of the value is correctly extended, therre should be a way to detect that
> `w2` is not just an ordinary const reference. I must admit I haven't come
> over the Clang code base yet so it's still a bit blurry to me (by the way if
> someone could kindly point me to some doc for developers...)
>
> Should I file a bug ? (or perhaps one already exists...)
>
> Matthieu.
>
> _______________________________________________
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> cfe-dev at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
>
>
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