[clang] [libcxx] [clang] Warn about memset/memcpy to NonTriviallyCopyable types (PR #111434)

[Nikolas Klauser via cfe-commits]

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@@ -102,7 +102,7 @@ struct __aliasing_iterator_wrapper {
 
     _LIBCPP_HIDE_FROM_ABI _Alias operator*() const _NOEXCEPT {
       _Alias __val;
-      __builtin_memcpy(&__val, std::__to_address(__base_), sizeof(value_type));
+      __builtin_memcpy(&__val, static_cast<const void*>(std::__to_address(__base_)), sizeof(value_type));
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philnik777 wrote:

@AaronBallman IIUC you're saying that it would be UB if some padding bytes ended up in the value representation of a different type, which could indeed arguably be UB. We can't have this scenario here though, since we only instantiate the type with integers as the `_Alias` and make sure that the source objects have a unique object representation via `__is_trivially_equality_comparable`. 

I think it would be interesting to diagnose such cases, but that seems quite complicated, since we'd have to check whether any padding bytes end up in non-padding bytes. (though definitely not impossible)


https://github.com/llvm/llvm-project/pull/111434