https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95349
--- Comment #37 from Richard Smith <richard-gccbugzilla at metafoo dot co.uk> --- (In reply to Richard Biener from comment #36) > The main issue I see is that this differing expectations of C and C++ are > impossible to get correct at the same time. That is a rather bold claim. I think you can satisfy both rule sets by using the C++ rule even in C. It is conservatively correct to discard the effective / dynamic type when you see a memcpy, and the C++ semantics require you to do so. The C semantics also appear to require the same thing, if you cannot track the destination back to either an object with a declared type or to a heap allocation; as described in comment#35, GCC gets this wrong and presumably miscompiles C code in some cases as a result. It seems to me that all you're allowed to do within the bounds of conformance is: #1 if you can track the destination back to an object with declared type in C code, then use its type as the effective type of the result #2 if you can track the destination back to a heap allocation in C code, then copy the effective type from source to destination #3 otherwise (in either C or C++) erase the effective type of the destination (#1 and #3 will presumably result in memcpy being replaced by some operation that updates the effective type, rather than being eliminated entirely.)
