This is both factually incorrect and philosophically unsound.

Every asm or IR instruction is emitted by the compiler. It isn't a "doesn't say otherwise" kind of thing. Whatever the motivations are, the compiler and its authors are responsible for everything that results.

"if you're out of the spec's guarantees you get whatever emergent behaviour occurs" is simply and patently not factual. There isn't a single compiler in existence for which this is true. Every compiler makes additional guarantees beyond the ISO standard, sometimes due to local dialect, sometimes due to other standards like POSIX, sometimes controlled by configuration or switches (e.g., -fwrapv).