dseve40868
2015-04-15 15:20
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Go是否会优化无法访问的if语句?

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?

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  • dongsha1544 2015-04-15 15:30
    已采纳

    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.

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