[cfe-dev] Addresses of referenced objects in clang 3.5

[David Blaikie]

(+Nick who had a hand in implementing this optimization)

I don't think there's a flag to control this, no.
On Sep 19, 2014 1:47 AM, "Richtarsky, Martin" <martin.richtarsky at sap.com>
wrote:

> Hi,
>
> since clang 3.5 code as below is optimized away with -O1, assuming that
> the address of the object
> can never be NULL:
>
> class A { };
>
> int func(A& a)
> {
>     if (&a)
>     {
>         return 1;
>     }
>     return 0;
> }
>
> int main()
> {
>     A &a = *reinterpret_cast<A *>(0);
>     return func(a);
> }
>
> clang++ -Wall -O1  ptrnull.cpp -o ptrnull
>
> ptrnull.cpp:5:10: warning: reference cannot be bound to dereferenced null
> pointer
> in well-defined C++ code; pointer may be assumed to always convert to true
> [-Wundefined-bool-conversion]
>     if (&a)
>     ~~   ^
> 1 warning generated.
>
>
> ./ptrnull
> Return code: 1
>
> This is as described in the release notes.
>
> When changing func() as follows the warning is not shown, but clang still
> performs
> the same optimization. Shouldn't the warning be shown here aswell?
>
> int func(A& a)
> {
>     A *aptr = &a;
>     if (aptr)
>     {
>         return 1;
>     }
>     return 0;
> }
>
> Is it possible to disable this optimization specifically (without
> resorting to -O0)
> to gradually fix codebases that rely on such checks? I saw that I can use
> -fsanitize=null, which helps, but disabling the optimization would still
> be the best temporary workaround.
>
> Thanks and Best regards,
> Martin
>
>
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>
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