[Wasm] export __callFunction_* only when a respective closure/lambda converter is used

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/dce/Dce.kt

@@ -53,6 +53,9 @@ private fun buildRoots(modules: List<IrModuleFragment>, context: WasmBackendCont
     add(context.irBuiltIns.throwableClass.owner)
     add(context.mainCallsWrapperFunction)
     add(context.fieldInitFunction)
+
+    // Remove all functions used to call a kotlin closure from JS side, reachable ones will be added back later.
+    removeAll(context.closureCallExports.values)
 }
 
 private inline fun List<IrModuleFragment>.onAllFiles(body: IrFile.() -> Unit) {

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/dce/WasmUsefulDeclarationProcessor.kt

@@ -23,6 +23,10 @@ internal class WasmUsefulDeclarationProcessor(
 
     private val unitGetInstance: IrSimpleFunction = context.findUnitGetInstanceFunction()
 
+    // The mapping from function for wrapping a kotlin closure/lambda with JS closure to function used to call a kotlin closure from JS side.
+    private val kotlinClosureToJsClosureConvertFunToKotlinClosureCallFun =
+        context.kotlinClosureToJsConverters.entries.associate { (k, v) -> v to context.closureCallExports[k] }
+
     override val bodyVisitor: BodyVisitorBase = object : BodyVisitorBase() {
         override fun visitConst(expression: IrConst<*>, data: IrDeclaration) = when (expression.kind) {
             is IrConstKind.Null -> expression.type.enqueueType(data, "expression type")
@@ -160,6 +164,8 @@ internal class WasmUsefulDeclarationProcessor(
 
         irFunction.getEffectiveValueParameters().forEach { it.enqueueValueParameterType(irFunction) }
         irFunction.returnType.enqueueType(irFunction, "function return type")
+
+        kotlinClosureToJsClosureConvertFunToKotlinClosureCallFun[irFunction]?.enqueue(irFunction, "kotlin closure to JS closure conversion", false)
     }
 
     override fun processSimpleFunction(irFunction: IrSimpleFunction) {

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/lower/JsInteropFunctionsLowering.kt

@@ -458,6 +458,8 @@ class JsInteropFunctionsLowering(val context: WasmBackendContext) : DeclarationT
             }
             +irReturn(info.resultAdapter.adaptIfNeeded(callInvoke, builder))
         }
+
+        // TODO find out a better way to export the such declarations only when it's required. Also, fix building roots for DCE, then.
         result.annotations += builder.irCallConstructor(context.wasmSymbols.jsExportConstructor, typeArguments = emptyList())
         additionalDeclarations += result
         return result

compiler/testData/codegen/box/size/add.kt

@@ -1,7 +1,7 @@
 // TARGET_BACKEND: WASM
 
-// WASM_DCE_EXPECTED_OUTPUT_SIZE: wasm 34_869 
-// WASM_DCE_EXPECTED_OUTPUT_SIZE:  mjs  6_359 
+// WASM_DCE_EXPECTED_OUTPUT_SIZE: wasm 29_800 
+// WASM_DCE_EXPECTED_OUTPUT_SIZE:  mjs  6_104 
 
 // FILE: test.kt
 

compiler/testData/codegen/box/size/helloWorld.kt

@@ -1,7 +1,7 @@
 // TARGET_BACKEND: WASM
 
-// WASM_DCE_EXPECTED_OUTPUT_SIZE: wasm 65_687 
-// WASM_DCE_EXPECTED_OUTPUT_SIZE:  mjs  6_458 
+// WASM_DCE_EXPECTED_OUTPUT_SIZE: wasm 60_691 
+// WASM_DCE_EXPECTED_OUTPUT_SIZE:  mjs  6_130 
 
 fun box(): String {
     println("Hello, World!")

compiler/testData/codegen/box/size/helloWorldDOM.kt

@@ -1,7 +1,7 @@
 // TARGET_BACKEND: WASM
 
-// WASM_DCE_EXPECTED_OUTPUT_SIZE: wasm 38_128 
-// WASM_DCE_EXPECTED_OUTPUT_SIZE:  mjs  6_798
+// WASM_DCE_EXPECTED_OUTPUT_SIZE: wasm 31_232 
+// WASM_DCE_EXPECTED_OUTPUT_SIZE:  mjs  6_659
 
 // FILE: test.kt
 

compiler/testData/codegen/box/size/ok.kt

@@ -1,6 +1,6 @@
 // TARGET_BACKEND: WASM
 
-// WASM_DCE_EXPECTED_OUTPUT_SIZE: wasm 34_917 
-// WASM_DCE_EXPECTED_OUTPUT_SIZE:  mjs  6_231 
+// WASM_DCE_EXPECTED_OUTPUT_SIZE: wasm 29_848 
+// WASM_DCE_EXPECTED_OUTPUT_SIZE:  mjs  5_976 
 
 fun box() = "OK"