On Mon, Dec 5, 2022 at 3:12 PM Marco Elver <elver@google.com> wrote:

> On Mon, 5 Dec 2022 at 14:26, Alexander Potapenko <glider@google.com>
> wrote:
> >
> > Recent Clang changes may cause it to delete calls of memcpy(), if the
> > source is an uninitialized volatile local.
> > This happens because passing a pointer to a volatile local into memcpy()
> > discards the volatile qualifier, giving the compiler a free hand to
> > optimize the memcpy() call away.
> >
> > To outsmart the compiler, we call __msan_memcpy() instead of memcpy()
> > in test_memcpy_aligned_to_aligned(), test_memcpy_aligned_to_unaligned()
> > and test_memcpy_aligned_to_unaligned2(), because it's the behavior of
> > __msan_memcpy() we are testing here anyway.
> >
> > Signed-off-by: Alexander Potapenko <glider@google.com>
>
> It might be nice to retain memcpy() calls somehow, as that tests
> end-to-end that the compiler does the right thing here i.e. replacing
> the memcpy() calls with instrumented versions.
>
> Does OPTIMIZER_HIDE_VAR() help? This should prevent the compiler from
> seeing it's uninitialized.
>
> It indeed does, thanks!
Let me send a v2.