If I have a constant like: ```const val DEBUG = false``` and then code like: ```if (DEBUG) { print...

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[cfleming]

If I have a constant like:

const val DEBUG = false

and then code like:

if (DEBUG) {
  println("Addthread: $thread")
}

If DEBUG is set to false, will the `println`s be totally compiled out of the class file?

[nanodeath]

you can decompile in IntelliJ and check. even if it's not decompiled, I'd expect the JVM to very quickly optimize it out at runtime

[ephemient]

https://github.com/JetBrains/kotlin/blob/f79afd67f46d3c2d5a13ff47ffc24007a5d97a46/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/JvmOptimizationLowering.kt#L192

[nanodeath]

huh. nice find!

[ephemient]

I was curious, tried it out; simple test case showed that it was eliminated, so ran kotlinc -Xlist-phases and just did a quick check of the ones that looked relevant

[ephemient]

but yeah even if the kotlin compiler didn't optimize it out, the JVM certainly will

[ephemient]

or if you're targeting android, dx/d8 will perform this optimization, and ART on the device will also perform this optimization

[cfleming]

Interesting, thanks for the investigation! I didn’t know about list-phases, I’ll have to play around with that. Certainly the JVM will optimise, but it’ll end up with more bytecode, string constants etc.

[cfleming]

Probably nothing in the big scheme of things, but my OCD will sleep a little better knowing that Kotlin will take care of it 🙂

[nanodeath]

well, a bool const should take up very little overhead

[cfleming]

Sure, I was referring to the constants etc involved in debug printing if it wasn’t optimised out.

[Vampire]

But is this also true for legacy backend?
The linked code is from the experimental ir backend.