[Wasm] UTF-8 encoding for strings (KT-79357)

Author: alex28sh

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/ir2wasm/ConstantData.kt

@@ -27,7 +27,7 @@ private fun addressToString(address: Int): String =
 class ConstantDataCharField(val value: WasmSymbol<Char>) : ConstantDataElement() {
     constructor(value: Char) : this(WasmSymbol(value))
 
-    override fun toBytes(): ByteArray = ByteArray(2).apply { value.owner.toLittleEndianBytes(this, 0) }
+    override fun toBytes(): ByteArray = ByteArray(2).apply { value.owner.toLittleEndianBytes(this, false, 0) }
 
     override fun dump(indent: String, startAddress: Int): String {
         return "${addressToString(startAddress)}: $indent i32   : ${value.owner}    ;;\n"
@@ -85,9 +85,12 @@ class ConstantDataIntArray(val value: List<WasmSymbol<Int>>) : ConstantDataEleme
 class ConstantDataCharArray(val value: List<WasmSymbol<Char>>) : ConstantDataElement() {
     constructor(value: CharArray) : this(value.map { WasmSymbol(it) })
 
+    private val isLatin: Boolean
+        get() = value.all { it.owner.code in 0..255 }
+
     override fun toBytes(): ByteArray {
-        return ByteArray(value.size * 2).apply {
-            value.forEachIndexed { index, symbol -> symbol.owner.toLittleEndianBytes(this, index * 2) }
+        return ByteArray(sizeInBytes).apply {
+            value.forEachIndexed { index, symbol -> symbol.owner.toLittleEndianBytes(this, isLatin, index * 2) }
         }
     }
 
@@ -96,7 +99,8 @@ class ConstantDataCharArray(val value: List<WasmSymbol<Char>>) : ConstantDataEle
         return "${addressToString(startAddress)}: $indent i16[] : ${value.map { it.owner }.toCharArray().contentToString()}   ;;\n"
     }
 
-    override val sizeInBytes: Int = value.size * CHAR_SIZE_BYTES
+    override val sizeInBytes: Int = value.size *
+            if (isLatin) BYTE_SIZE_BYTES else CHAR_SIZE_BYTES
 }
 
 class ConstantDataStruct(val elements: List<ConstantDataElement>) : ConstantDataElement() {
@@ -138,7 +142,9 @@ fun Int.toLittleEndianBytes(to: ByteArray, offset: Int) {
     to[offset + 3] = (this ushr 24).toByte()
 }
 
-fun Char.toLittleEndianBytes(to: ByteArray, offset: Int) {
+fun Char.toLittleEndianBytes(to: ByteArray, isLatin: Boolean, offset: Int) {
     to[offset] = (this.code and 0xFF).toByte()
-    to[offset + 1] = (this.code ushr Byte.SIZE_BITS).toByte()
+    if (!isLatin) {
+        to[offset + 1] = (this.code ushr Byte.SIZE_BITS).toByte()
+    }
 }

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/ir2wasm/DeclarationGenerator.kt

@@ -623,10 +623,12 @@ fun generateConstExpression(
         is IrConstKind.String -> {
             val stringValue = expression.value as String
             val (literalAddress, literalPoolId) = context.referenceStringLiteralAddressAndId(stringValue)
+            val isLatin = stringValue.all { it.code in 0..255 }
             body.commentGroupStart { "const string: \"$stringValue\"" }
             body.buildConstI32Symbol(literalPoolId, location)
             body.buildConstI32Symbol(literalAddress, location)
             body.buildConstI32(stringValue.length, location)
+            body.buildConstI32(if (isLatin) 1 else 0, location)
             body.buildCall(context.referenceFunction(backendContext.wasmSymbols.stringGetLiteral), location)
             body.commentGroupEnd()
         }

libraries/stdlib/wasm/builtins/kotlin/String.kt

@@ -157,13 +157,23 @@ public actual class String internal @WasmPrimitiveConstructor constructor(
 internal inline fun WasmCharArray.createString(): String =
     String(null, this.len(), this)
 
-internal fun stringLiteral(poolId: Int, startAddress: Int, length: Int): String {
+internal fun stringLiteral(poolId: Int, startAddress: Int, length: Int, isLatin: Int = 0): String {
     val cached = stringPool[poolId]
     if (cached !== null) {
         return cached
     }
 
-    val chars = array_new_data0<WasmCharArray>(startAddress, length)
+    val chars: WasmCharArray
+    if (isLatin == 0) {
+        chars = array_new_data0<WasmCharArray>(startAddress, length)
+    } else {
+        val bytes = array_new_data0<WasmByteArray>(startAddress, length)
+        chars = WasmCharArray(length)
+        for (i in 0..<length) {
+            val chr = bytes.get(i).toInt().toChar()
+            chars.set(i, chr)
+        }
+    }
     val newString = String(null, length, chars)
     stringPool[poolId] = newString
     return newString