Go编译器技巧

Question

I read in a talk that the Go compiler will aggressively remove code that isn't used in the output binary. The talk which I can't find used this for adding some code useful to testing. Does anybody have more information on how this works? Are there talks on advanced testing techniques?

Answer 1

Five things that make Go fast

Dave Cheney

Dead Code Elimination

func Test() bool { return false }

func Expensive() {
  if Test() {
      // something expensive
  }
}

In this example, although the function Test always returns false, Expensive cannot know that without executing it.

When Test is inlined, we get something like this

func Expensive() {
  if false {
      // something expensive is
      // now unreachable
  }
}

The compiler now knows that the expensive code is unreachable.

Not only does this save the cost of calling Test, it saves compiling or running any of the expensive code that is now unreachable.

---

For example, adding some code useful to testing,

func Complicated() {
    if Test() {
        // something for testing
    }
}

Switching Test from

func Test() bool { return false }

inlined

func Complicated() {
    if false {
        // something for testing
        // unreachable
    }
}

to

func Test() bool { return true }

inlined

func Complicated() {
    if true {
        // something for testing
        // reachable
    }
}

can be useful to include code just for testing.