The language specification covers the semantics and correctness of the code. Excepting some very specific things such as tail call elimination that also touch on semantics, optimizations do not belong in the language specification.
If we did have a principle saying that you can't get clever with optimization or take advantage of your language's optimizer, that would imply that the past 15-20 years of growth of Web technology was based on an invalid foundation: the v8 JavaScript engine and people's efforts to learn how to use it effectively and push what's possible in a browser.
You'd also have much less impressive video games, and your smartphone would have worse battery life.
If we did have a principle saying that you can't get clever with optimization or take advantage of your language's optimizer, that would imply that the past 15-20 years of growth of Web technology was based on an invalid foundation: the v8 JavaScript engine and people's efforts to learn how to use it effectively and push what's possible in a browser.
You'd also have much less impressive video games, and your smartphone would have worse battery life.