WASM: Implement simple try/catch codegen

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

@@ -64,7 +64,7 @@ fun compileWasm(
 
     wasmPhases.invokeToplevel(phaseConfig, context, moduleFragment)
 
-    val compiledWasmModule = WasmCompiledModuleFragment()
+    val compiledWasmModule = WasmCompiledModuleFragment(context.irBuiltIns)
     val codeGenerator = WasmModuleFragmentGenerator(context, compiledWasmModule)
     codeGenerator.generateModule(moduleFragment)
 

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

@@ -23,7 +23,6 @@ import org.jetbrains.kotlin.ir.types.*
 import org.jetbrains.kotlin.ir.util.*
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitorVoid
 import org.jetbrains.kotlin.ir.visitors.acceptVoid
-import org.jetbrains.kotlin.psi2ir.intermediate.generateExpressionValue
 import org.jetbrains.kotlin.wasm.ir.*
 
 class BodyGenerator(val context: WasmFunctionCodegenContext) : IrElementVisitorVoid {
@@ -67,6 +66,26 @@ class BodyGenerator(val context: WasmFunctionCodegenContext) : IrElementVisitorV
         body.buildThrow(context.tagIdx)
     }
 
+    override fun visitTry(aTry: IrTry) {
+        assert(aTry.isCanonical(irBuiltIns)) { "expected canonical try/catch" }
+        assert(aTry.type != irBuiltIns.nothingType) { "shouldn't happen" }
+
+        val resultType = context.transformBlockResultType(aTry.type)
+        body.buildTry(null, resultType)
+        generateExpression(aTry.tryResult)
+
+        body.buildCatch(context.tagIdx)
+
+        // Exception object is on top of the stack, store it into the local
+        aTry.catches.single().catchParameter.symbol.let {
+            context.defineLocal(it)
+            body.buildSetLocal(context.referenceLocal(it))
+        }
+        generateExpression(aTry.catches.single().result)
+
+        body.buildEnd()
+    }
+
     override fun visitTypeOperator(expression: IrTypeOperatorCall) {
         when (expression.operator) {
             IrTypeOperator.REINTERPRET_CAST -> generateExpression(expression.argument)

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

@@ -7,6 +7,7 @@ package org.jetbrains.kotlin.backend.wasm.ir2wasm
 
 import org.jetbrains.kotlin.backend.common.push
 import org.jetbrains.kotlin.backend.wasm.lower.WasmSignature
+import org.jetbrains.kotlin.ir.IrBuiltIns
 import org.jetbrains.kotlin.ir.declarations.IrDeclarationWithName
 import org.jetbrains.kotlin.ir.declarations.IrExternalPackageFragment
 import org.jetbrains.kotlin.ir.symbols.*
@@ -14,7 +15,7 @@ import org.jetbrains.kotlin.ir.util.fqNameWhenAvailable
 import org.jetbrains.kotlin.ir.util.getPackageFragment
 import org.jetbrains.kotlin.wasm.ir.*
 
-class WasmCompiledModuleFragment {
+class WasmCompiledModuleFragment(val irBuiltIns: IrBuiltIns) {
     val functions =
         ReferencableAndDefinable<IrFunctionSymbol, WasmFunction>()
     val globals =
@@ -33,12 +34,20 @@ class WasmCompiledModuleFragment {
         ReferencableElements<WasmSignature, Int>()
     val stringLiteralId =
         ReferencableElements<String, Int>()
-    val tagFuncType = WasmFunctionType("ex_handling_tag", listOf(WasmAnyRef), emptyList())
-    val tag = WasmTag(tagFuncType)
 
     val runtimeTypes =
         ReferencableAndDefinable<IrClassSymbol, WasmGlobal>()
 
+    val tagFuncType = WasmFunctionType(
+        "ex_handling_tag",
+        listOf(
+            WasmRefNullType(WasmHeapType.Type(gcTypes.reference(irBuiltIns.throwableClass)))
+        ),
+        emptyList()
+    )
+    val tag = WasmTag(tagFuncType)
+
+
     val classes = mutableListOf<IrClassSymbol>()
     val interfaces = mutableListOf<IrClassSymbol>()
     val virtualFunctions = mutableListOf<IrSimpleFunctionSymbol>()

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/utils/Utils.kt

@@ -0,0 +1,21 @@
+/*
+ * 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 org.jetbrains.kotlin.backend.wasm.utils
+
+import org.jetbrains.kotlin.ir.IrBuiltIns
+import org.jetbrains.kotlin.ir.expressions.IrTry
+
+// Backed codegen can only handle try/catch in canonical form.
+// Canonical form for the try/catch:
+// try {
+//   ...exprs
+// } catch (e: Throwable) {
+//   ...exprs
+// }
+// no-finally
+fun IrTry.isCanonical(builtIns: IrBuiltIns) =
+    catches.singleOrNull()?.catchParameter?.symbol?.owner?.type == builtIns.throwableType &&
+    finallyExpression == null

wasm/wasm.ir/src/org/jetbrains/kotlin/wasm/ir/WasmExpressionBuilder.kt

@@ -76,6 +76,12 @@ abstract class WasmExpressionBuilder {
         buildInstr(WasmOp.THROW, WasmImmediate.TagIdx(tagIdx))
     }
 
+    @Suppress("UNUSED_PARAMETER")
+    fun buildTry(label: String?, resultType: WasmType? = null) {
+        numberOfNestedBlocks++
+        buildInstr(WasmOp.TRY, WasmImmediate.BlockType.Value(resultType))
+    }
+
     fun buildCatch(tagIdx: Int) {
         buildInstr(WasmOp.CATCH, WasmImmediate.TagIdx(tagIdx))
     }