Does Go optimize out unreachable if-statements?

Question

Go has a very unfortunate lack of built-in assertions. I want to implement them this way:

const ASSERT = true

func SomeFunction() {
        if ASSERT && !some_condition_that_should_always_be_true() {
                panic("Error message or object.")
        }
}

My question is will the if-statement be optimized out if I define const ASSERT = false?

Answer 1

As noted by the people in the comments to your question, it's implementation-specific.

gc does remove it. You can build your program with -gcflags '-S' and see that the ASSERT part is not in the binary.

E.g. compile the following code with -gcflags '-S', and you'll see that the code on lines 8 and 9 is included, but change Assert to be false, and they won't be there in the asm listing.

package main

const Assert = true

var cond = true

func main() {
    if Assert && !cond {
        panic("failed")
    }
}

EDIT:

As for gccgo, it removes this code at -O1 and above. You can see it by compiling the same code with

go build -compiler gccgo -gccgoflags '-O1' main.go

and then doing

objdump -S main

to see the annotated assembly.