Does anyone have any advice for how to reduce the size of my final JS output? I'm worried I might be...

# compose-web

[David Herman]

Does anyone have any advice for how to reduce the size of my final JS output? I'm worried I might be writing my code in a way that accidentally prevents DCE from working without realizing it, for example.

[David Herman]

(I'm writing both a C4W app and some libraries -- not sure if the way I'm writing the libraries could be improved)

[David Herman]

A great place to start would be if I could get some sort of report about what code is being kept alive vs what's getting eliminated. I'm paranoid some stuff is sticking around that I don't expect.

[Oleksandr Karpovich [JB]]

I recall there was a compiler flag to report DCE for kjs. I tried to find it quickly, but it's inconvenient to do on the smartphone. I'll look for it later on a laptop.

[David Herman]

No rush! Thanks! Now that I know there's a compiler flag, I can look into it too later.

[Oleksandr Karpovich [JB]]

The flag I recalled was https://youtrack.jetbrains.com/issue/KT-45059/KJS-IR-Add-possibility-for-runtime-diagnostics-of-DCE-result

But it's only for runtime diagnostics, not like a log of the DCE actions/decisions.

Perhaps another flag https://github.com/JetBrains/kotlin/blob/master/compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/K2JSCompilerArguments.kt#L199 could be helpful

[David Herman]

Thank you for following up!

[bashor]

There is a compiler option -Xir-dce-print-reachability-info
Then DCE will print to stdout what and why was marked as reachable.

from.fqn -> to.fqn // comment

[sdeleuze]

@bashor @David Herman I struggle to make it working on a basic Compose for Web project. I configured:

js(IR) {
	browser()
	binaries.executable()
	compilations.all {
		kotlinOptions {
			freeCompilerArgs += "-Xir-dce-print-reachability-info"
			freeCompilerArgs.forEach(::println)
		}
	}
}

Then I run ./gradlew clean compileProductionExecutableKotlinJs but I see no reachability info on the standard output. What did I miss?

[David Herman]

(Ah glad to hear you're digging into this -- I'm still a bit backlogged and never got a chance)

[sdeleuze]

Ok so let's wait Zalim feedback.

[bashor]

AFAIR compilations.all { inside `js`/`wasm` block affects only first fase of compilation — klib generation.

Also, it turned out there is a bug so if you use -Xir-dce-print-reachability-info you also need restore -Xir-dce (cc @Ilya Goncharov [JB])

Final snippet could look like:

tasks.withType<org.jetbrains.kotlin.gradle.tasks.Kotlin2JsCompile>().configureEach {
    kotlinOptions.freeCompilerArgs += listOf(
        "-Xir-dce", 
        "-Xir-dce-print-reachability-info"
    )
}

[bashor]

you find printed result in kotlin-daemon.*.log inside your $TMPDIR

[bashor]

alternatively you can pass -Pkotlin.compiler.execution.strategy=in-process to the gradle so you will get compiler stdout right into your terminal

[sdeleuze]

Ok thanks!

[sdeleuze]

Tested, it works as expected with this configuration.