I find it every time funny that when using languages that want to give you "total control" over the execution of your code (mostly C/C++) you actually almost never know what code gets executed in the end.

It depends on the compiler, it's version, it's flags, and likely "the position of the moon".

Of course the compiler is only allowed to do transformations that the spec permits. But it's impossible for a human being to anticipate the exact outcome. It's more like: "Compiler, do something that has the same outcome as this code I show you here". The output can be than something that doesn't resemble the input even slightly!

There's obviously nothing wrong when the compiler is so smart that it sees some patterns and transforms your code into something much more efficient. Only that there's not much difference to what happens when you use a high level language. In both cases you in fact don't control the exact code that gets executed, and in both cases you rely on the smartness of your compiler to produce some efficient code, "whatever" you've written.

That's why I think it's mostly a function of the code-style how performant or efficient some language can be (to some extend of course). When you write low-level style code (even in a high level language) a smart compiler will (hopefully) create something like what you would get form writing your code in C/C++.