Hi, LLVM and Clang developer here.<p>I don&#x27;t see anyone being blasé about this. The issue comes down to something really simple:<p>- The compiler can emit substantially simpler code if it has a guarantee from the platform&#x27;s implementation of memcpy.<p>- The compiler authors thought they had such a guarantee and so chose to leverage it.<p>Now, maybe they don&#x27;t have that guarantee on all platforms. If that&#x27;s the case, its flat out and simply a bug in the compiler. And you&#x27;ll find folks on that bug arguing that it doesn&#x27;t actually hold, which is good and important.<p>But it&#x27;s actually quite reasonable to have a guarantee from a platform&#x27;s libc that this will work and leverage that. The compiler isn&#x27;t generating C code or code bound by any standard. This is about two parts of the implementation of C agreeing about what internal invariants will hold.<p>The problem this bug highlights (and it is a real problem, and not one anyone takes lightly) is that we have insufficient agreement about these invariants, both for certain platforms (glibc) and even within LLVM. Fixing this remains absolutely critical, but may only involve documenting the agreement.