[Wasm][Stdlib] Add public APIs for linear memory access

Needed for interop with APIs that use linear memory.

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/WasmSymbols.kt

@@ -211,7 +211,6 @@ class WasmSymbols(
     val nullableDoubleIeee754Equals = getInternalFunction("nullableDoubleIeee754Equals")
 
     val unsafeGetScratchRawMemory = getInternalFunction("unsafeGetScratchRawMemory")
-    val unsafeGetScratchRawMemorySize = getInternalFunction("unsafeGetScratchRawMemorySize")
     val startCoroutineUninterceptedOrReturnIntrinsics =
         (0..2).map { getInternalFunction("startCoroutineUninterceptedOrReturnIntrinsic$it") }
 

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

@@ -568,15 +568,9 @@ class BodyGenerator(
             }
 
             wasmSymbols.unsafeGetScratchRawMemory -> {
-                // TODO: This drops size of the allocated segment. Instead we can check that it's in bounds for better error messages.
-                body.buildDrop()
                 body.buildConstI32Symbol(context.scratchMemAddr)
             }
 
-            wasmSymbols.unsafeGetScratchRawMemorySize -> {
-                body.buildConstI32Symbol(WasmSymbol(context.scratchMemSizeInBytes))
-            }
-
             wasmSymbols.wasmArrayCopy -> {
                 val immediate = WasmImmediate.GcType(
                     context.referenceGcType(call.getTypeArgument(0)!!.getRuntimeClass(irBuiltIns).symbol)
@@ -891,6 +885,8 @@ class BodyGenerator(
                                 WasmImmediate.HeapType(WasmHeapType.Type(getReferenceGcType()))
                             WasmImmediateKind.TYPE_IDX ->
                                 WasmImmediate.TypeIdx(getReferenceGcType())
+                            WasmImmediateKind.MEMORY_IDX ->
+                                WasmImmediate.MemoryIdx(0)
 
                             else ->
                                 error("Immediate $imm is unsupported")

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

@@ -65,7 +65,6 @@ class WasmCompiledModuleFragment(val irBuiltIns: IrBuiltIns) {
     val initFunctions = mutableListOf<FunWithPriority>()
 
     val scratchMemAddr = WasmSymbol<Int>()
-    val scratchMemSizeInBytes = 65_536
 
     val stringPoolSize = WasmSymbol<Int>()
 
@@ -127,11 +126,8 @@ class WasmCompiledModuleFragment(val irBuiltIns: IrBuiltIns) {
             currentDataSectionAddress += typeInfoElement.sizeInBytes
         }
 
-        // Reserve some memory to pass complex exported types (like strings). It's going to be accessible through 'unsafeGetScratchRawMemory'
-        // runtime call from stdlib.
         currentDataSectionAddress = alignUp(currentDataSectionAddress, INT_SIZE_BYTES)
         scratchMemAddr.bind(currentDataSectionAddress)
-        currentDataSectionAddress += scratchMemSizeInBytes
 
         bind(classIds.unbound, klassIds)
         interfaceId.unbound.onEachIndexed { index, entry -> entry.value.bind(index) }
@@ -176,9 +172,10 @@ class WasmCompiledModuleFragment(val irBuiltIns: IrBuiltIns) {
 
         val typeInfoSize = currentDataSectionAddress
         val memorySizeInPages = (typeInfoSize / 65_536) + 1
-        val memory = WasmMemory(WasmLimits(memorySizeInPages.toUInt(), memorySizeInPages.toUInt()))
+        val memory = WasmMemory(WasmLimits(memorySizeInPages.toUInt(), null /* "unlimited" */))
 
         // Need to export the memory in order to pass complex objects to the host language.
+        // Export name "memory" is a WASI ABI convention.
         exports += WasmExport.Memory("memory", memory)
 
         val importedFunctions = functions.elements.filterIsInstance<WasmFunction.Imported>()

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

@@ -28,9 +28,6 @@ class WasmModuleCodegenContext(
     val stringPoolSize: WasmSymbol<Int>
         get() = wasmFragment.stringPoolSize
 
-    val scratchMemSizeInBytes: Int
-        get() = wasmFragment.scratchMemSizeInBytes
-
     fun transformType(irType: IrType): WasmType {
         return with(typeTransformer) { irType.toWasmValueType() }
     }