| ▲ | pjc50 an hour ago | |
> Some of which is not actually UB because the implementation defines it No - if something is UB in the spec, it's UB. The implementation will do something, sure, but what it does is not fixed and may even change based on compiler version and optimization level. > DWORD-sized memory access is atomic on Windows because Microsoft said it is Well, Intel said it is. Mind you I don't think there are any 32-bit native architectures where aligned dword access isn't atomic. Unaligned, on the other hand ... | ||
| ▲ | trumpdong 22 minutes ago | parent | next [-] | |
"Undefined behavior" in the C standard literally means "behavior which this C standard does not put any requirements on" - it says so in the definitions section of the C standard. Other things can still put requirements on it. MSVC isn't just a C++ compiler - it's a C++ compiler for x64 Windows and therefore follows the rules of C++, x64, and Windows all at once. | ||
| ▲ | simiones an hour ago | parent | prev [-] | |
> No - if something is UB in the spec, it's UB. A compiler is still free to ignore the spec and declare that something is not UB. However, this is very much compiler based, not platform based. Windows might guarantee that aligned DWORD-sized memory accesses are atomic, but that doesn't mean Clang when compiling for Windows would respect this - but MSVC might. | ||