JS IR: Remove nested blocks from bodies

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsLoweringPhases.kt

@@ -14,6 +14,7 @@ import org.jetbrains.kotlin.backend.common.lower.optimizations.PropertyAccessorI
 import org.jetbrains.kotlin.backend.common.phaser.*
 import org.jetbrains.kotlin.ir.backend.js.lower.*
 import org.jetbrains.kotlin.ir.backend.js.lower.calls.CallsLowering
+import org.jetbrains.kotlin.ir.backend.js.lower.cleanup.CleanupLowering
 import org.jetbrains.kotlin.ir.backend.js.lower.coroutines.JsSuspendFunctionsLowering
 import org.jetbrains.kotlin.ir.backend.js.lower.coroutines.RemoveSuspendLambdas
 import org.jetbrains.kotlin.ir.backend.js.lower.inline.CopyInlineFunctionBodyLowering
@@ -579,6 +580,12 @@ private val objectUsageLoweringPhase = makeBodyLoweringPhase(
     description = "Transform IrGetObjectValue into instance generator call"
 )
 
+private val cleanupLoweringPhase = makeBodyLoweringPhase(
+    { CleanupLowering() },
+    name = "CleanupLowering",
+    description = "Clean up IR before codegen"
+)
+
 val loweringList = listOf<Lowering>(
     scriptRemoveReceiverLowering,
     validateIrBeforeLowering,
@@ -650,6 +657,7 @@ val loweringList = listOf<Lowering>(
     objectDeclarationLoweringPhase,
     objectUsageLoweringPhase,
     callsLoweringPhase,
+    cleanupLoweringPhase,
     validateIrAfterLowering
 )
 

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/cleanup/CleanupLowering.kt

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2010-2019 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.ir.backend.js.lower.cleanup
+
+import org.jetbrains.kotlin.backend.common.BodyLoweringPass
+import org.jetbrains.kotlin.ir.IrElement
+import org.jetbrains.kotlin.ir.declarations.IrDeclaration
+import org.jetbrains.kotlin.ir.expressions.*
+import org.jetbrains.kotlin.ir.util.transformFlat
+import org.jetbrains.kotlin.ir.visitors.IrElementVisitorVoid
+import org.jetbrains.kotlin.ir.visitors.acceptChildrenVoid
+import org.jetbrains.kotlin.ir.visitors.acceptVoid
+
+class CleanupLowering : BodyLoweringPass {
+    override fun lower(irBody: IrBody, container: IrDeclaration) {
+        irBody.acceptVoid(BlockRemover())
+    }
+}
+
+private class BlockRemover: IrElementVisitorVoid {
+    override fun visitElement(element: IrElement) {
+        element.acceptChildrenVoid(this)
+    }
+
+    private fun process(container: IrStatementContainer) {
+        container.statements.transformFlat { statement ->
+            (statement as? IrStatementContainer)?.statements
+        }
+    }
+
+    override fun visitBlockBody(body: IrBlockBody) {
+        super.visitBlockBody(body)
+
+        process(body)
+    }
+
+    override fun visitContainerExpression(expression: IrContainerExpression) {
+        super.visitContainerExpression(expression)
+
+        process(expression)
+    }
+}