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
