[legalcorrection]

Oh really? Then why does every compiler I use have a parameter to turn off strict aliasing?

You cite to a source that contradicts you. In the llvm blog post: "It is also worth pointing out that both Clang and GCC nail down a few behaviors that the C standard leaves undefined."

[protomolecule]

Sometimes a compiler gives a guarantee that a particular UB is always handled in a specific way, but you cannot generalize this to all UB.

Added 'in general' to my comment to make this explicit.