[Wasm]: Make the Wasm backend also generate NothingValueException.

In commit 00f6197, the test in compiler/testData/codegen/box/nothingValue/nothingValueException.kt was muted for the WebAssembly backend. This commit fixes the issue and re-enables the test.


Merge-request: KT-MR-24551
Merged-by: Charlie Zhang <charles.zhang@jetbrains.com>

Author: Charles Zhang

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/KotlinNothingValueExceptionLowering.kt

@@ -42,7 +42,7 @@ open class KotlinNothingValueExceptionLowering(
                 // Replace call 'foo' of type 'kotlin.Nothing' with a block:
                 //
                 //  {
-                //      [ call 'foo' with type: 'kotlin.Unit' ]
+                //      [ call 'foo' with type: 'kotlin.Nothing' ]
                 //      call ThrowKotlinNothingValueException(): Nothing
                 //  }: Nothing
                 //

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

@@ -96,6 +96,11 @@ private val lateinitPhase = makeIrModulePhase(
     name = "LateinitLowering",
 )
 
+private val kotlinNothingValueExceptionPhase = makeIrModulePhase(
+    ::KotlinNothingValueExceptionLowering,
+    name = "KotlinNothingValueException",
+)
+
 private val rangeContainsLoweringPhase = makeIrModulePhase(
     ::RangeContainsLowering,
     name = "RangeContainsLowering",
@@ -680,6 +685,12 @@ fun getWasmLowerings(
         addContinuationToFunctionCallsLoweringPhase,
         generateMainFunctionWrappersPhase,
 
+        // We need to generate nothing value exceptions after suspend
+        // functions have been lowered so that suspend functions
+        // declared to return nothing get a chance to get lowered
+        // without the exception being inserted.
+        kotlinNothingValueExceptionPhase,
+
         invokeOnExportedFunctionExitLowering,
 
         tryCatchCanonicalization,

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

@@ -74,8 +74,7 @@ class WasmSymbols(
     val throwTypeCastWithInfoException = CallableIds.THROW_CCE_WITH_INFO.functionSymbol()
     override val throwIAE = CallableIds.THROW_IAE.functionSymbol()
     val throwNoBranchMatchedException = CallableIds.throwNoBranchMatchedException.functionSymbol()
-    override val throwKotlinNothingValueException: IrSimpleFunctionSymbol
-        get() = TODO()
+    override val throwKotlinNothingValueException = CallableIds.throwKotlinNothingValueException.functionSymbol()
     override val stringBuilder = ClassIds.StringBuilder.classSymbol()
     override val getContinuation = CallableIds.getContinuation.functionSymbol()
     override val returnIfSuspended = CallableIds.returnIfSuspended.functionSymbol()
@@ -409,6 +408,7 @@ private object CallableIds {
     val THROW_CCE_WITH_INFO = "THROW_CCE_WITH_INFO".wasmCallableId
     val THROW_IAE = "THROW_IAE".wasmCallableId
     val throwNoBranchMatchedException = "throwNoBranchMatchedException".wasmCallableId
+    val throwKotlinNothingValueException = "throwKotlinNothingValueException".wasmCallableId
     val getContinuation = "getContinuation".wasmCallableId
     val returnIfSuspended = "returnIfSuspended".wasmCallableId
     val enumValueOfIntrinsic = "enumValueOfIntrinsic".wasmCallableId

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

@@ -27,6 +27,7 @@ import org.jetbrains.kotlin.ir.util.isNullable
 import org.jetbrains.kotlin.ir.util.isSubtypeOfClass
 import org.jetbrains.kotlin.ir.visitors.IrVisitorVoid
 import org.jetbrains.kotlin.ir.visitors.acceptVoid
+import org.jetbrains.kotlin.ir.visitors.acceptChildrenVoid
 import org.jetbrains.kotlin.wasm.config.WasmConfigurationKeys
 import org.jetbrains.kotlin.wasm.ir.*
 import org.jetbrains.kotlin.wasm.ir.source.location.SourceLocation
@@ -65,7 +66,19 @@ class BodyGenerator(
     internal fun generateExpression(expression: IrExpression) {
         expression.acceptVoid(this)
 
-        if (expression.type.isNothing()) {
+        // Checks if it is safe to assume the statement doesn't return
+        // (e.g. throws an exception or loops infinitely)
+        //
+        // Takes into account cases like `fun <T> foo(): T = Any() as
+        // T`, which could be used as `foo<Nothing>()` and terminate
+        // despite the call type `Nothing`.
+        //
+        // Assumes that only functions with explicit return type
+        // `Nothing` do not return.
+        //
+        // Also see KotlinNothingValueExceptionLowering.kt
+        if (expression.type.isNothing() &&
+                !(expression is IrCall && !expression.symbol.owner.returnType.isNothing())) {
             // TODO Ideally, we should generate unreachable only for specific cases and preferable on declaration site. 
             body.buildUnreachableAfterNothingType()
         }
@@ -74,7 +87,7 @@ class BodyGenerator(
     // Generates code for the given IR element but *never* leaves anything on the stack.
     private fun generateAsStatement(statement: IrExpression) {
         generateExpression(statement)
-        if (statement.type != wasmSymbols.voidType) {
+        if (statement.type != wasmSymbols.voidType && !statement.type.isNothing()) {
             body.buildDrop(SourceLocation.NoLocation("DROP"))
         }
     }

compiler/testData/codegen/box/nothingValue/nothingValueException.kt

@@ -1,6 +1,3 @@
-// IGNORE_BACKEND: WASM_JS, WASM_WASI
-// WASM_MUTE_REASON: REFLECTION
-
 fun <T> something(): T = Any() as T
 
 class Context<T>

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

@@ -1,7 +1,7 @@
 // TARGET_BACKEND: WASM_JS
 
 // RUN_THIRD_PARTY_OPTIMIZER
-// WASM_DCE_EXPECTED_OUTPUT_SIZE: wasm  55_229
+// WASM_DCE_EXPECTED_OUTPUT_SIZE: wasm  55_926
 // WASM_DCE_EXPECTED_OUTPUT_SIZE: mjs    5_940
 // WASM_OPT_EXPECTED_OUTPUT_SIZE:           76
 

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

@@ -1,7 +1,7 @@
 // TARGET_BACKEND: WASM
 
 // RUN_THIRD_PARTY_OPTIMIZER
-// WASM_DCE_EXPECTED_OUTPUT_SIZE: wasm  55_530
+// WASM_DCE_EXPECTED_OUTPUT_SIZE: wasm  56_266
 // WASM_DCE_EXPECTED_OUTPUT_SIZE: mjs    5_871
 // WASM_OPT_EXPECTED_OUTPUT_SIZE:        3_911
 

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

@@ -1,7 +1,7 @@
 // TARGET_BACKEND: WASM_JS
 
 // RUN_THIRD_PARTY_OPTIMIZER
-// WASM_DCE_EXPECTED_OUTPUT_SIZE: wasm 55_635
+// WASM_DCE_EXPECTED_OUTPUT_SIZE: wasm 56_329
 // WASM_DCE_EXPECTED_OUTPUT_SIZE:  mjs  6_103
 // WASM_OPT_EXPECTED_OUTPUT_SIZE:       4_131
 

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

@@ -1,7 +1,7 @@
 // TARGET_BACKEND: WASM
 
 // RUN_THIRD_PARTY_OPTIMIZER
-// WASM_DCE_EXPECTED_OUTPUT_SIZE: wasm 60_209
+// WASM_DCE_EXPECTED_OUTPUT_SIZE: wasm 60_909
 // WASM_DCE_EXPECTED_OUTPUT_SIZE:  mjs  5_806
 // WASM_OPT_EXPECTED_OUTPUT_SIZE:       4_822
 
@@ -68,4 +68,4 @@ fun box(): String {
     if (ClassWithCompanionWithConst.MAX != 5) return "Fail simple companion object with const val"
     SimpleWithDifferentMembers
     return "OK"
-}
+}

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

@@ -1,10 +1,10 @@
 // TARGET_BACKEND: WASM
 
 // RUN_THIRD_PARTY_OPTIMIZER
-// WASM_DCE_EXPECTED_OUTPUT_SIZE: wasm 55_280
+// WASM_DCE_EXPECTED_OUTPUT_SIZE: wasm 55_977
 // WASM_DCE_EXPECTED_OUTPUT_SIZE:  mjs  5_806
 // WASM_OPT_EXPECTED_OUTPUT_SIZE:       3_849
 
 // IGNORE_BACKEND: WASM_WASI
 
-fun box() = "OK"
+fun box() = "OK"