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Benchmarks: pass -Xwasm-use-new-exception-proposal to Wasm linkTask - #5787
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Oleksandr Karpovich (eymar) merged 1 commit intoNov 3, 2026
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In JetBrains#5359, -Xwasm-use-new-exception-proposal was added to compilation.compileTaskProvider, which only compiles .kt sources into .klib archives. Pass it to binary.linkTask (KotlinJsIrLink) as well so the linked .wasm binary uses standard WebAssembly exnref (try_table).
Oleksandr Karpovich (eymar)
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Thanks for the fix!
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Daniel Lehmann (danleh)
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Build the Compose Multiplatform benchmarks from upstream master (1574503571, which includes JetBrains/compose-multiplatform#5787 passing -Xwasm-use-new-exception-proposal to the Wasm linkTask) instead of the JetStream 3.0 hotfix branch (ok/jetstream3_hotfix, 84dad4d3f6), overriding compose.version to 1.13.0-beta01. This moves Kotlin from 2.2.20-Beta2 to 2.4.20 (stable), Compose from 1.8.2 to 1.13.0-beta01 (which includes the PR #3411 fix for per-frame JobCancellationException/Error stack allocation in RectManager and PR #3269/#3484 Skia wrapper reuse fixes), and Skiko from a custom 0.9.4.3 build to 0.156.0, while emitting standard WebAssembly exnref (try_table/throw_ref) with zero legacy try/catch instructions. Compiler option added in compiler-options.patch (both on compile and KotlinJsIrLink tasks): - -Xwasm-kclass-fqn=false: Works around KT-91066, where Kotlin 2.3+'s KClassImpl.hashCode() allocates and hashes "$packageName.$typeName" on every call (triggered on every Compose modifier node lookup). Removed workarounds: - The hotfix branch and its custom Skiko build. - use-beta-toolchain.patch: master uses a stable Kotlin (2.4.20). - jstag-workaround.patch: Safari's WebAssembly.JSTag fixes have shipped. - hook-print.patch: Kotlin's glue logs through console, and benchmark.js now silences console.log and console.warn unless verbose is set. - The skipFunMain global in benchmark.js, which nothing reads. Kept, rebased: empty-main-function.patch and skiko-disable-instantiate.patch (updated for Skiko 0.156.0's awaitSkikoCore). Also rewrite static imports in Kotlin 2.4's compose-benchmarks-benchmarks.import-object.mjs via sed in build.sh, instantiate compose-benchmarks-benchmarks.wasm directly in benchmark.js (replacing compose-benchmarks-benchmarks.uninstantiated.mjs), and disable window.caches in benchmark.js so Compose 1.12+'s ResourceWebCache uses the in-memory preload fetch polyfill in browsers just as in JS shells. TODOs once upstream updates ship: - Update CMP_REV to a newer compose-multiplatform commit once Compose 1.13.0 is stable (~mid-December 2026) and drop the explicit -Pcompose.version=1.13.0-beta01 override in build.sh. - Remove compiler-options.patch (-Xwasm-kclass-fqn=false) once KT-91066 is fixed and backported. Part of WebKit#277.
Daniel Lehmann (danleh)
added a commit
to danleh/JetStream
that referenced
this pull request
Nov 3, 2026
Build the Compose Multiplatform benchmarks from upstream master (1574503571, which includes JetBrains/compose-multiplatform#5787 passing -Xwasm-use-new-exception-proposal to the Wasm linkTask) instead of the JetStream 3.0 hotfix branch (ok/jetstream3_hotfix, 84dad4d3f6), overriding compose.version to 1.13.0-beta01. This moves Kotlin from 2.2.20-Beta2 to 2.4.20 (stable), Compose from 1.8.2 to 1.13.0-beta01 (which includes the PR #3411 fix for per-frame JobCancellationException/Error stack allocation in RectManager and PR #3269/#3484 Skia wrapper reuse fixes), and Skiko from a custom 0.9.4.3 build to 0.156.0, while emitting standard WebAssembly exnref (try_table/throw_ref) with zero legacy try/catch instructions. Compiler option added in compiler-options.patch (both on compile and KotlinJsIrLink tasks): - -Xwasm-kclass-fqn=false: Works around KT-91066, where Kotlin 2.3+'s KClassImpl.hashCode() allocates and hashes "$packageName.$typeName" on every call (triggered on every Compose modifier node lookup). Removed workarounds: - The hotfix branch and its custom Skiko build. - use-beta-toolchain.patch: master uses a stable Kotlin (2.4.20). - jstag-workaround.patch: Safari's WebAssembly.JSTag fixes have shipped. - hook-print.patch: Kotlin's glue logs through console, and benchmark.js now silences console.log and console.warn unless verbose is set. - The skipFunMain global in benchmark.js, which nothing reads. Kept, rebased: empty-main-function.patch and skiko-disable-instantiate.patch (updated for Skiko 0.156.0's awaitSkikoCore). Also rewrite static imports in Kotlin 2.4's compose-benchmarks-benchmarks.import-object.mjs via sed in build.sh, instantiate compose-benchmarks-benchmarks.wasm directly in benchmark.js (replacing compose-benchmarks-benchmarks.uninstantiated.mjs), and disable window.caches in benchmark.js so Compose 1.12+'s ResourceWebCache uses the in-memory preload fetch polyfill in browsers just as in JS shells. TODOs once upstream updates ship: - Update CMP_REV to a newer compose-multiplatform commit once Compose 1.13.0 is stable (~mid-December 2026) and drop the explicit -Pcompose.version=1.13.0-beta01 override in build.sh. - Remove compiler-options.patch (-Xwasm-kclass-fqn=false) once KT-91066 is fixed and backported. Part of WebKit#277.
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In #5359,
-Xwasm-use-new-exception-proposalwas added tocompilation.compileTaskProviderinbenchmarks/multiplatform/benchmarks/build.gradle.kts.In the Kotlin Gradle plugin for
wasmJs,compilation.compileTaskProvider(Kotlin2JsCompile) only compiles.ktsources into.klibarchives. Lowering.klibIR into the final.wasmbinary happens inbinary.linkTask(KotlinJsIrLink, such ascompileProductionExecutableKotlinWasmJs), which has its owncompilerOptionsblock and does not inheritfreeCompilerArgsfromcompileTaskProvider. As a result,compose-benchmarks-benchmarks.wasmwas still being linked with the legacy Wasm exception handling instructions (try/catch).Passing
-Xwasm-use-new-exception-proposaltolinkTaskas well switches the generated.wasmbinary to standard WebAssemblyexnref(try_table).We ran into this while updating the
Kotlin-compose-wasmworkload in WebKit/JetStream (WebKit/JetStream#277).cc Zalim Bashorov (@bashor) Oleksandr Karpovich (@eymar) Konstantin (@terrakok)
Testing
Built
:benchmarks:compileProductionExecutableKotlinWasmJsand verified withwasm-toolsthat the emittedcompose-benchmarks-benchmarks.wasmusestry_tableinstead of legacytry/catchinstructions.Release Notes
N/A