8000 Wasm: Use builtin string constants from JS string builtins. · sjrd/scala-js@64edcce · GitHub
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Wasm: Use builtin string constants from JS string builtins.
In addition to builtin functions, the JS string builtins proposal provides a way to import (valid UTF-8) string literals from a dedicated module. Instead of using a custom data segment, we now import all the strings we can from that builtin module. For the rare cases where we need a string literal that is not a valid UTF-16 string (and therefore cannot be encoded into valid UTF-8), we use custom imports that we fill in from the JS side. This alternate encoding is a lot more economical in terms of code size. It shaves off 5% of the fastLink output, and 8.5% of the fullLink output. Moreover, it means our string literals are constant expression globals, which we can directly use in the initialization of `typeData` constant structs.
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‎linker/shared/src/main/scala/org/scalajs/linker/backend/wasmemitter/ClassEmitter.scala

Lines changed: 6 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -212,8 +212,7 @@ class ClassEmitter(coreSpec: CoreSpec) {
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coreSpec.semantics.runtimeClassNameMapper,
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className.nameString
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)
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val nameDataValue: List[wa.Instr] =
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ctx.stringPool.getConstantStringDataInstr(nameStr)
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val nameValue = ctx.stringPool.getConstantStringInstr(nameStr)
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val kind = className match {
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case ObjectClass => KindObject
@@ -299,8 +298,10 @@ class ClassEmitter(coreSpec: CoreSpec) {
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elemsInstrs :+ wa.ArrayNewFixed(genTypeID.reflectiveProxies, reflectiveProxies.size)
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}
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nameDataValue :::
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(
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List(
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// name
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nameValue,
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// kind
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wa.I32Const(kind),
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// specialInstanceTypes
@@ -312,8 +313,6 @@ class ClassEmitter(coreSpec: CoreSpec) {
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List(
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// componentType - always `null` since this method is not used for array types
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wa.RefNull(watpe.HeapType(genTypeID.typeData)),
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// name - initially `null`; filled in by the `typeDataName` helper
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wa.RefNull(watpe.HeapType.NoExtern),
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// the classOf instance - initially `null`; filled in by the `createClassOf` helper
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wa.RefNull(watpe.HeapType(genTypeID.ClassStruct)),
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// arrayOf, the typeData of an array of this type - initially `null`; filled in by the `arrayTypeData` helper
@@ -327,6 +326,7 @@ class ClassEmitter(coreSpec: CoreSpec) {
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// Generated instructions create an array of reflective proxy structs, where each struct
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// contains the ID of the reflective proxy and a reference to the actual method implementation.
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reflectiveProxiesInstrs
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)
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}
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private def genTypeDataGlobal(className: ClassName, typeDataTypeID: wanme.TypeID,
@@ -1366,7 +1366,7 @@ class ClassEmitter(coreSpec: CoreSpec) {
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ctx.moduleBuilder.addImport(
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wamod.Import(
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"__scalaJSExportSetters",
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ExportSettersModule,
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exportedName,
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wamod.ImportDesc.Func(
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functionID,

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