Fix for https://youtrack.jetbrains.com/issue/KT-36980

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/llvm/IrToBitcode.kt

@@ -1818,11 +1818,7 @@ internal class CodeGeneratorVisitor(val context: Context, val lifetimes: Map<IrE
         val bbExit = returnableBlockScope.bbExit
         if (bbExit != null) {
             if (!functionGenerationContext.isAfterTerminator()) {                 // TODO should we solve this problem once and for all
-                if (returnableBlockScope.resultPhi != null) {
-                    functionGenerationContext.unreachable()
-                } else {
-                    functionGenerationContext.br(bbExit)
-                }
+                functionGenerationContext.unreachable()
             }
             functionGenerationContext.positionAtEnd(bbExit)
         }

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/lower/ReturnsInsertionLowering.kt

@@ -14,8 +14,7 @@ import org.jetbrains.kotlin.ir.builders.irReturn
 import org.jetbrains.kotlin.ir.declarations.IrConstructor
 import org.jetbrains.kotlin.ir.declarations.IrFile
 import org.jetbrains.kotlin.ir.declarations.IrFunction
-import org.jetbrains.kotlin.ir.expressions.IrBlockBody
-import org.jetbrains.kotlin.ir.types.classifierOrNull
+import org.jetbrains.kotlin.ir.expressions.*
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitorVoid
 import org.jetbrains.kotlin.ir.visitors.acceptChildrenVoid
 import org.jetbrains.kotlin.ir.visitors.acceptVoid
@@ -32,14 +31,25 @@ internal class ReturnsInsertionLowering(val context: Context) : FileLoweringPass
             override fun visitFunction(declaration: IrFunction) {
                 declaration.acceptChildrenVoid(this)
 
-                val body = declaration.body
-                if ((declaration is IrConstructor || declaration.returnType.classifierOrNull == symbols.unit) && body != null) {
+                val body = declaration.body ?: return
+                if (declaration is IrConstructor || declaration.returnType == context.irBuiltIns.unitType) {
                     val irBuilder = context.createIrBuilder(declaration.symbol, declaration.endOffset, declaration.endOffset)
                     irBuilder.run {
                          (body as IrBlockBody).statements += irReturn(irGetObject(symbols.unit))
                     }
                 }
             }
+
+            override fun visitBlock(expression: IrBlock) {
+                expression.acceptChildrenVoid(this)
+                if (expression !is IrReturnableBlock) return
+                if (expression.inlineFunctionSymbol?.owner?.returnType == context.irBuiltIns.unitType) {
+                    val irBuilder = context.createIrBuilder(expression.symbol, expression.endOffset, expression.endOffset)
+                    irBuilder.run {
+                        expression.statements += irReturn(irGetObject(symbols.unit))
+                    }
+                }
+            }
         })
     }
 }

backend.native/tests/build.gradle

@@ -2994,6 +2994,11 @@ task inline_correctOrderFunctionReference(type: KonanLocalTest) {
     source = "codegen/inline/correctOrderFunctionReference.kt"
 }
 
+task inline_coercionToUnit(type: KonanLocalTest) {
+    goldValue = "kotlin.Unit\n"
+    source = "codegen/inline/coercionToUnit.kt"
+}
+
 task classDeclarationInsideInline(type: KonanLocalTest) {
     source = "codegen/inline/classDeclarationInsideInline.kt"
     goldValue = "test1: 1.0\n1\ntest2\n"

backend.native/tests/codegen/inline/coercionToUnit.kt

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the LICENSE file.
+ */
+
+package codegen.inline.coercionToUnit
+
+import kotlin.test.*
+
+fun <T> myRun(action: () -> T): T = action()
+
+fun foo(n: Number, b: Boolean) {
+    n.let {
+        if (b) return@let
+
+        myRun() { 42 }
+    }
+}
+
+@Test fun runTest() {
+    println(foo(42, false))
+}