With Kotlin `1 7 20 Beta` I try to use Binaryen to optimize

Question

With Kotlin `1 7 20 Beta` I try to use Binaryen to optimize the generated Wasm but it fails ```wasm opt build compileSync main productionExecutable kotlin add wasm wasm o build compileSync main productionExecutable kotlin add wasm opt wasm enable nontrapping float to int enable typed function references enable gc enable reference types enable exception handling O3 inline functions with loops traps never happen fast math parse exception Recursion groups not allowed with equirecursive typing at 0 15 Fatal error parsing wasm``` Could you please share what version parameters I should use The related sample is available on <https github com sdeleuze wasm footprint tree main kotlin>

sdeleuze · Answer

The app I compile is ```fun main add 2 3 fun add a Int b Int = a + b``` And in the generated 1 1M wasm most of the footprint is taken by collection and exception infra ``` grep $kotlin collections build compileSync main productionExecutable kotlin add wasm wat | wc l 774 grep Exception build compileSync main productionExecutable kotlin add wasm wat | wc l 346``` Is it due to the fact I am not using `wasm opt`

Svyatoslav Kuzmich [JB] · Answer

Flags that we use by default listed <https github com JetBrains kotlin blob 1 7 20 libraries tools kotlin gradle plugin src common kotlin org jetbrains kotlin gradle targets js binaryen BinaryenExec kt L30|here> I think that the lack of ` hybrid` is whats causing the error

Svyatoslav Kuzmich [JB] · Answer

We use version <https github com JetBrains kotlin blob 1 7 20 libraries tools kotlin gradle plugin src common kotlin org jetbrains kotlin gradle targets js binaryen BinaryenRootExtension kt L29|109>

sdeleuze · Answer

Nice with ` hybrid` that works as expected ``` exa l build compileSync main productionExecutable kotlin rw r r 15k seb 18 Aug 19 41 add wasm opt wasm rw r r 4 5k seb 14 Aug 13 58 add wasm mjs rw r r 156k seb 14 Aug 13 58 add wasm wasm rw r r 1 1M seb 14 Aug 13 58 add wasm wat``` After optimization the generated Wasm file is 10x smaller

sdeleuze · Answer

< Svyatoslav Kuzmich JB > Do you know how `wasm opt` is able to optimize the size that much Is it doing a second pass of code removal of unreachable code paths after Kotlin Wasm