WASM: NFC. Move IrBlockBody visit into body builder

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

@@ -339,6 +339,10 @@ class BodyGenerator(val context: WasmFunctionCodegenContext) : IrElementVisitorV
         return true
     }
 
+    override fun visitBlockBody(body: IrBlockBody) {
+        body.statements.forEach(::statementToWasmInstruction)
+    }
+
     override fun visitContainerExpression(expression: IrContainerExpression) {
         val statements = expression.statements
         if (statements.isEmpty()) {

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

@@ -137,14 +137,8 @@ class DeclarationGenerator(val context: WasmModuleCodegenContext) : IrElementVis
         val exprGen = functionCodegenContext.bodyGen
         val bodyBuilder = BodyGenerator(functionCodegenContext)
 
-        when (val body = declaration.body) {
-            is IrBlockBody ->
-                for (statement in body.statements) {
-                    bodyBuilder.statementToWasmInstruction(statement)
-                }
-
-            else -> error("Unexpected body $body")
-        }
+        require(declaration.body is IrBlockBody) { "Only IrBlockBody is supported" }
+        declaration.body?.acceptVoid(bodyBuilder)
 
         // Return implicit this from constructions to avoid extra tmp
         // variables on constructor call sites.
@@ -155,8 +149,8 @@ class DeclarationGenerator(val context: WasmModuleCodegenContext) : IrElementVis
         }
 
         // Add unreachable if function returns something but not as a last instruction.
-        if (wasmFunctionType.resultTypes.isNotEmpty() && declaration.body is IrBlockBody) {
-            // TODO: Add unreachable only if needed
+        // We can do a separate lowering which adds explicit returns everywhere instead.
+        if (wasmFunctionType.resultTypes.isNotEmpty()) {
             exprGen.buildUnreachable()
         }