WASM: Implement wasm-native strings part 1

There are several changes here but they all required for at least one test to pass.
- Implemented String class and several utility functions using built-in CharArray
- Added new constant memory segment to hold string literals and required funcs to work with them
- Added very crude mostly incorrect rudimentary ability to pass strings back to javascript

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

@@ -154,7 +154,3 @@ public class Char private constructor(public val value: Char) : Comparable<Char>
         public const val SIZE_BITS: Int = 16
     }
 }
-
-@WasmImport("runtime", "Char_toString")
-private fun charToString(c: Char): String = implementedAsIntrinsic
-

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

@@ -341,7 +341,7 @@ public class Byte private constructor(public val value: Byte) : Number(), Compar
         wasm_i32_eq(this.toInt(), other.toInt())
 
     public override fun toString(): String =
-        byteToStringImpl(this)
+        TODO("Wasm: string coercion")
 
     public override inline fun hashCode(): Int =
         this.toInt()
@@ -352,10 +352,6 @@ public class Byte private constructor(public val value: Byte) : Number(), Compar
         implementedAsIntrinsic
 }
 
-@WasmImport("runtime", "coerceToString")
-private fun byteToStringImpl(byte: Byte): String =
-    implementedAsIntrinsic
-
 /**
  * Represents a 16-bit signed integer.
  */
@@ -684,7 +680,8 @@ public class Short private constructor(public val value: Short) : Number(), Comp
     public override fun equals(other: Any?): Boolean =
         other is Short && wasm_i32_eq(this.toInt(), other.toInt())
 
-    public override fun toString(): String = shortToStringImpl(this)
+    public override fun toString(): String =
+        TODO("Wasm: string coercion")
 
     public override inline fun hashCode(): Int =
         this.toInt()
@@ -695,9 +692,6 @@ public class Short private constructor(public val value: Short) : Number(), Comp
         implementedAsIntrinsic
 }
 
-@WasmImport("runtime", "coerceToString")
-private fun shortToStringImpl(x: Short): String = implementedAsIntrinsic
-
 /**
  * Represents a 32-bit signed integer.
  */
@@ -1066,7 +1060,7 @@ public class Int private constructor(val value: Int) : Number(), Comparable<Int>
         other is Int && wasm_i32_eq(this, other)
 
     public override fun toString(): String =
-        intToStringImpl(this)
+        TODO("Wasm: string coercion")
 
     public override inline fun hashCode(): Int =
         this
@@ -1092,10 +1086,6 @@ public class Int private constructor(val value: Int) : Number(), Comparable<Int>
         implementedAsIntrinsic
 }
 
-@WasmImport("runtime", "coerceToString")
-private fun intToStringImpl(x: Int): String =
-    implementedAsIntrinsic
-
 /**
  * Represents a 64-bit signed integer.
  */
@@ -1462,9 +1452,8 @@ public class Long private constructor(val value: Long) : Number(), Comparable<Lo
     public override fun equals(other: Any?): Boolean =
         other is Long && wasm_i64_eq(this, other)
 
-    // TODO: Implement proper Long.toString
     public override fun toString(): String =
-        toDouble().toString()
+        TODO("Wasm: string coercion")
 
     public override fun hashCode(): Int =
         ((this ushr 32) xor this).toInt()
@@ -1769,7 +1758,7 @@ public class Float private constructor(public val value: Float) : Number(), Comp
         other is Float && this.equals(other)
 
     public override fun toString(): String =
-        floatToStringImpl(this)
+        TODO("Wasm: string coercion")
 
     public override inline fun hashCode(): Int =
         bits()
@@ -1779,10 +1768,6 @@ public class Float private constructor(public val value: Float) : Number(), Comp
     internal fun bits(): Int = implementedAsIntrinsic
 }
 
-@WasmImport("runtime", "coerceToString")
-private fun floatToStringImpl(x: Float): String =
-    implementedAsIntrinsic
-
 /**
  * Represents a double-precision 64-bit IEEE 754 floating point number.
  */
@@ -2086,7 +2071,7 @@ public class Double private constructor(public val value: Double) : Number(), Co
         other is Double && this.bits() == other.bits()
 
     public override fun toString(): String =
-        doubleToStringImpl(this)
+        TODO("Wasm: string coercion")
 
     public override inline fun hashCode(): Int = bits().hashCode()
 
@@ -2095,7 +2080,3 @@ public class Double private constructor(public val value: Double) : Number(), Co
     internal fun bits(): Long =
         implementedAsIntrinsic
 }
-
-@WasmImport("runtime", "coerceToString")
-private fun doubleToStringImpl(x: Double): String =
-    implementedAsIntrinsic

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

@@ -11,18 +11,17 @@ import kotlin.wasm.internal.*
  * The `String` class represents character strings. All string literals in Kotlin programs, such as `"abc"`, are
  * implemented as instances of this class.
  */
-@WasmAutoboxed
-public class String constructor(public val string: String) : Comparable<String>, CharSequence {
+public class String internal constructor(internal val chars: CharArray) : Comparable<String>, CharSequence {
     public companion object;
 
     /**
      * Returns a string obtained by concatenating this string with the string representation of the given [other] object.
      */
     public operator fun plus(other: Any?): String =
-        stringPlusImpl(this, other.toString())
+        String(chars + other.toString().chars)
 
     public override val length: Int
-        get() = stringLengthImpl(this)
+        get() = chars.size
 
     /**
      * Returns the character of this string at the specified [index].
@@ -30,43 +29,49 @@ public class String constructor(public val string: String) : Comparable<String>,
      * If the [index] is out of bounds of this string, throws an [IndexOutOfBoundsException] except in Kotlin/JS
      * where the behavior is unspecified.
      */
-    public override fun get(index: Int): Char =
-        stringGetCharImpl(this, index)
+    public override fun get(index: Int): Char = chars[index]
 
     public override fun subSequence(startIndex: Int, endIndex: Int): CharSequence =
-        stringSubSequenceImpl(this, startIndex, endIndex)
+        TODO("todo")
 
     public override fun compareTo(other: String): Int =
-        stringCompareToImpl(this, other)
+        TODO("todo")
 
     public override fun equals(other: Any?): Boolean {
         if (other is String)
-            return this.compareTo(other) == 0
+            return chars.contentEquals(other.chars)
+            //return this.compareTo(other) == 0
         return false
     }
 
     public override fun toString(): String = this
 
-    // TODO: Implement
+    // TODO: this is not nice
     public override fun hashCode(): Int = 10
 }
 
-@JsFun("(it, other) => it + String(other)")
-private fun stringPlusImpl(it: String, other: String): String =
-    implementedAsIntrinsic
+internal fun stringLiteral(startAddr: Int, length: Int) = String(unsafeRawMemoryToCharArray(startAddr, length))
 
-@JsFun("(it) => it.length")
-private fun stringLengthImpl(it: String): Int =
-    implementedAsIntrinsic
+internal fun charToString(c: Char): String = String(charArrayOf(c))
 
-@WasmImport("runtime", "String_getChar")
-private fun stringGetCharImpl(it: String, index: Int): Char =
-    implementedAsIntrinsic
+internal fun wasm_string_eq(x: String, y: String): Boolean = x.equals(y)
 
-@WasmImport("runtime", "String_compareTo")
-private fun stringCompareToImpl(it: String, other: String): Int =
-    implementedAsIntrinsic
-
-@WasmImport("runtime", "String_subsequence")
-private fun stringSubSequenceImpl(string: String, startIndex: Int, endIndex: Int): String =
-    implementedAsIntrinsic
+//@JsFun("(it, other) => it + String(other)")
+//private fun stringPlusImpl(it: String, other: String): String =
+//    implementedAsIntrinsic
+//
+//@JsFun("(it) => it.length")
+//private fun stringLengthImpl(it: String): Int =
+//    implementedAsIntrinsic
+//
+//@WasmImport("runtime", "String_getChar")
+//private fun stringGetCharImpl(it: String, index: Int): Char =
+//    implementedAsIntrinsic
+//
+//@WasmImport("runtime", "String_compareTo")
+//private fun stringCompareToImpl(it: String, other: String): Int =
+//    implementedAsIntrinsic
+//
+//@WasmImport("runtime", "String_subsequence")
+//private fun stringSubSequenceImpl(string: String, startIndex: Int, endIndex: Int): String =
+//    implementedAsIntrinsic

libraries/stdlib/wasm/internal/kotlin/wasm/internal/ImportExport.kt

@@ -0,0 +1,18 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package kotlin.wasm.internal
+
+// This is called when exported function returns a string. It writes [i32 length, [i16 chars ...]] into a temporary raw memory area and
+// returns pointer to the start of it.
+// Note: currently there is a single temporary raw memory area so it's not possible to export more than one string at a time.
+internal fun exportStringRet(src: String): Int {
+    val retAddr = unsafeGetScratchRawMemory(INT_SIZE_BYTES + src.length * CHAR_SIZE_BYTES)
+    wasm_i32_store(retAddr, src.length)
+    unsafeCharArrayToRawMemory(src.toCharArray(), retAddr + INT_SIZE_BYTES)
+    return retAddr
+}
+
+// See importStringToJs for the JS-side import for strings

libraries/stdlib/wasm/internal/kotlin/wasm/internal/Runtime.kt

@@ -5,10 +5,34 @@
 
 package kotlin.wasm.internal
 
-@WasmImport("runtime", "String_getLiteral")
-internal fun stringLiteral(index: Int): String =
+internal const val CHAR_SIZE_BYTES = 2
+internal const val INT_SIZE_BYTES = 4
+
+internal fun unsafeRawMemoryToChar(addr: Int) = wasm_i32_load16_u(addr).toChar()
+
+internal fun unsafeRawMemoryToCharArray(startAddr: Int, length: Int): CharArray {
+    val ret = CharArray(length)
+    for (i in 0 until length) {
+        ret[i] = unsafeRawMemoryToChar(startAddr + i * CHAR_SIZE_BYTES)
+    }
+    return ret
+}
+
+// Returns a pointer into a temporary scratch segment in the raw wasm memory. Aligned by 4.
+// Note: currently there is single such segment for a whole wasm module, so use with care.
+@ExcludedFromCodegen
+internal fun unsafeGetScratchRawMemory(sizeBytes: Int): Int =
     implementedAsIntrinsic
 
+// Assumes there is enough space at the destination, fails with wasm trap otherwise.
+internal fun unsafeCharArrayToRawMemory(src: CharArray, dstAddr: Int) {
+    var curAddr = dstAddr
+    for (i in src) {
+        wasm_i32_store16(curAddr, i)
+        curAddr += CHAR_SIZE_BYTES
+    }
+}
+
 @WasmReinterpret
 internal fun unsafeNotNull(x: Any?): Any =
     implementedAsIntrinsic

libraries/stdlib/wasm/internal/kotlin/wasm/internal/WasmInstructions.kt

@@ -308,4 +308,13 @@ public external fun wasm_i64_trunc_sat_f32_s(a: Float): Long
 public external fun wasm_i64_trunc_sat_f64_s(a: Double): Long
 
 @WasmOp(WasmOp.I32_LOAD)
-public external fun wasm_i32_load(x: Int): Int
+public external fun wasm_i32_load(x: Int): Int
+
+@WasmOp(WasmOp.I32_LOAD16_U)
+public external fun wasm_i32_load16_u(x: Int): Int
+
+@WasmOp(WasmOp.I32_STORE)
+public external fun wasm_i32_store(addr: Int, i: Int): Unit
+
+@WasmOp(WasmOp.I32_STORE16)
+public external fun wasm_i32_store16(addr: Int, c: Char): Unit

libraries/stdlib/wasm/internal/kotlin/wasm/internal/WasmMath.kt

@@ -12,7 +12,3 @@ fun wasm_i32_compareTo(x: Int, y: Int): Int =
 
 fun wasm_i64_compareTo(x: Long, y: Long): Int =
     wasm_i64_ge_s(x, y).toInt() - wasm_i64_le_s(x, y).toInt()
-
-@WasmImport("runtime", "String_equals")
-fun wasm_string_eq(x: String, y: String): Boolean =
-    implementedAsIntrinsic

libraries/stdlib/wasm/src/kotlin/Text.kt

@@ -287,7 +287,7 @@ public actual fun CharArray.concatToString(startIndex: Int, endIndex: Int): Stri
  */
 @SinceKotlin("1.3")
 @ExperimentalStdlibApi
-public actual fun String.toCharArray(): CharArray = TODO("Wasm stdlib: Text")
+public actual fun String.toCharArray(): CharArray = this.chars
 
 /**
  * Returns a [CharArray] containing characters of this string or its substring.