-Wclass-memaccess warning should be in -Wextra, not -Wall

[Martin Sebor]

On 07/05/2018 05:14 PM, Soul Studios wrote:
> Simply because a struct has a constructor does not mean it isn't a
> viable target/source for use with memcpy/memmove/memset.

As the documentation that Segher quoted explains, it does
mean exactly that.

Some classes have user-defined copy and default ctors with
the same effect as memcpy/memset.  In modern C++ those ctors
should be defaulted (= default) and GCC should emit optimal
code for them.  In fact, in loops they can result in more
efficient code than the equivalent memset/memcpy calls.  In
any case, "native" operations lend themselves more readily
to code analysis than raw memory accesses and as a result
allow all compilers (not just GCC) do a better a job of
detecting bugs or performing interesting transformations
that they may not be able to do otherwise.

> Having benchmarked the alternatives memcpy/memmove/memset definitely
> makes a difference in various scenarios.

Please open bugs with small test cases showing
the inefficiencies so the optimizers can be improved.

Martin