Why are compilers so stupid?

Question

I always wonder why compilers can\'t figure out simple things that are obvious to the human eye. They do lots of simple optimizations, but never something even a little bit

Answer 1

Absolute optimization is an undecidable problem, that means, there is no Turing machine (and, therefore, no computer program) that can yield the optimal version of ANY given program.

Some simple optimizations can be (and, in fact, are) done, but, in the examples you gave...

1. To detect that your first program always prints zero, the compiler would have to detect that x remains constant despite all the loop iterations. How can you explain (I know, it's not the best word, but I can't come up with another) that to a compiler?

2. How can the compiler know that the StringBuilder is the right tool for the job without ANY reference to it?

In a real-world application, if efficiency is critical in a part of your application, it must be written in a low-level language like C. (Haha, seriously, I wrote this?)