[PATCH] Check for null pointers given to memcpy with ubsan

[Alexey Samsonov]

In http://reviews.llvm.org/D9673#170474, @nlopes wrote:

> > Wait a second, won't UBSan handle this automatically if memcpy/memmove are 
>
> >  declared with __attribute__((nonnull)) in the header? Otherwise, is there 
>
> >  a change to the standard that imposes these additional constraints on 
>
> >  memcpy/memmove?
>
>
> Not really. memcpy/memmove calls are handled by CGBultin and not CGCall. 
>  It's a different code path.
> Nuno


Interesting. I think that if we decide to implement such a check, we shouldn't depend on
attributes specified in the headers, so `nonnull-attribute` is no longer relevant. There are another
kind of compiler builtins which worth extra checks, and which don't even require headers - e.g. behavior of __builtin_ctz(0)
is undefined. I think we should implement another check kind `-fsanitize=builtin` that would verify arguments of
various builtin functions.


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http://reviews.llvm.org/D9673

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