[simonster]

It's true that implementation makes a bigger difference to performance than language features, but language features can indeed affect speed. One clear example is that a language that checks for integer overflow will be slower than a language that doesn't. There are a lot of situations where there's no way you could optimize out the extra instructions you'd need to check for overflow.

Some language features are easy to optimize away for some common cases (e.g. array bounds checks, so that your program throws an exception instead of segfaulting), but you can't optimize these if, for example, you're iterating over data you read from a file using indices you also read from that file.