psi2ir: Consistently use type unit for statements

These changes allow us to accurately distinguish between statements and
expressions in the IR.

This also fixes the types of non-exhaustive conditional statements.

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/ExpressionCodegen.kt

@@ -599,7 +599,10 @@ class ExpressionCodegen(
         SwitchGenerator(expression, data, this).generate()?.let { return it }
 
         val endLabel = Label()
-        val exhaustive = expression.branches.any { it.condition.isTrueConst() }
+        val exhaustive = expression.branches.any { it.condition.isTrueConst() } && !expression.type.isUnit()
+        assert(exhaustive || expression.type.isUnit()) {
+            "non-exhaustive conditional should return Unit: ${expression.dump()}"
+        }
         for (branch in expression.branches) {
             val elseLabel = Label()
             if (branch.condition.isFalseConst() || branch.condition.isTrueConst()) {
@@ -614,26 +617,21 @@ class ExpressionCodegen(
             } else {
                 branch.condition.accept(this, data).coerceToBoolean().jumpIfFalse(elseLabel)
             }
-            val result = branch.result.accept(this, data).coerce(expression.type).materialized
+            val result = branch.result.accept(this, data)
             if (!exhaustive) {
                 result.discard()
-            } else if (branch.condition.isTrueConst()) {
+            } else {
-                // The rest of the expression is dead code.
+                val materializedResult = result.coerce(expression.type).materialized
-                mv.mark(endLabel)
+                if (branch.condition.isTrueConst()) {
-                return result
+                    // The rest of the expression is dead code.
+                    mv.mark(endLabel)
+                    return materializedResult
+                }
             }
             mv.goTo(endLabel)
             mv.mark(elseLabel)
         }
         mv.mark(endLabel)
-        // NOTE: using a non-exhaustive if/when as an expression is invalid, so it should theoretically
-        //       always return Unit. However, with the current frontend this is not always the case.
-        //       Most notably, 1. when all branches return/break/continue, the type is Nothing;
-        //       2. the frontend may sometimes infer Any instead of Unit, probably due to a bug
-        //       (see compiler/testData/codegen/box/controlStructures/ifIncompatibleBranches.kt).
-        //       It should still be safe to produce a soon-to-be-discarded Unit. (What is not ok is
-        //       inserting *any* code here, though, as its line number will be that of the last line
-        //       of the last branch.)
         return immaterialUnitValue
     }
 

compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/BranchingExpressionGenerator.kt

@@ -16,7 +16,6 @@
 
 package org.jetbrains.kotlin.psi2ir.generators
 
-import org.jetbrains.kotlin.builtins.KotlinBuiltIns
 import org.jetbrains.kotlin.ir.UNDEFINED_OFFSET
 import org.jetbrains.kotlin.ir.builders.buildStatement
 import org.jetbrains.kotlin.ir.builders.irIfThenMaybeElse
@@ -38,8 +37,6 @@ import org.jetbrains.kotlin.utils.SmartList
 class BranchingExpressionGenerator(statementGenerator: StatementGenerator) : StatementGeneratorExtension(statementGenerator) {
 
     fun generateIfExpression(expression: KtIfExpression): IrExpression {
-        val resultType = getInferredTypeWithImplicitCastsOrFail(expression).toIrType()
-
         var ktLastIf: KtIfExpression = expression
         val irBranches = SmartList<IrBranch>()
         var irElseBranch: IrExpression? = null
@@ -61,7 +58,7 @@ class BranchingExpressionGenerator(statementGenerator: StatementGenerator) : Sta
             }
         }
 
-        return createIrWhen(expression, irBranches, irElseBranch, resultType)
+        return createIrWhen(expression, irBranches, irElseBranch, getExpressionTypeWithCoercionToUnitOrFail(expression).toIrType())
     }
 
     private fun generateEmptyBlockForMissingBranch(ktLastIf: KtIfExpression) =
@@ -100,16 +97,10 @@ class BranchingExpressionGenerator(statementGenerator: StatementGenerator) : Sta
     fun generateWhenExpression(expression: KtWhenExpression): IrExpression {
         val irSubject = generateWhenSubject(expression)
 
-        val inferredType = getInferredTypeWithImplicitCastsOrFail(expression)
+        val irWhen = IrWhenImpl(
-
+            expression.startOffsetSkippingComments, expression.endOffset,
-        val resultType = when {
+            getExpressionTypeWithCoercionToUnitOrFail(expression).toIrType(), IrStatementOrigin.WHEN
-            // Non-exhaustive when can only be used as statement.
+        )
-            expression.isExhaustiveWhen() -> inferredType.toIrType()
-            KotlinBuiltIns.isNothing(inferredType) -> inferredType.toIrType()
-            else -> context.irBuiltIns.unitType
-        }
-
-        val irWhen = IrWhenImpl(expression.startOffsetSkippingComments, expression.endOffset, resultType, IrStatementOrigin.WHEN)
 
         for (ktEntry in expression.entries) {
             if (ktEntry.isElse) {
@@ -170,12 +161,22 @@ class BranchingExpressionGenerator(statementGenerator: StatementGenerator) : Sta
     private fun generateWhenBody(expression: KtWhenExpression, irSubject: IrVariable?, irWhen: IrWhen): IrExpression =
         if (irSubject == null) {
             if (irWhen.branches.isEmpty())
-                IrBlockImpl(expression.startOffsetSkippingComments, expression.endOffset, context.irBuiltIns.unitType, IrStatementOrigin.WHEN)
+                IrBlockImpl(
+                    expression.startOffsetSkippingComments,
+                    expression.endOffset,
+                    context.irBuiltIns.unitType,
+                    IrStatementOrigin.WHEN
+                )
             else
                 irWhen
         } else {
             if (irWhen.branches.isEmpty()) {
-                val irBlock = IrBlockImpl(expression.startOffsetSkippingComments, expression.endOffset, context.irBuiltIns.unitType, IrStatementOrigin.WHEN)
+                val irBlock = IrBlockImpl(
+                    expression.startOffsetSkippingComments,
+                    expression.endOffset,
+                    context.irBuiltIns.unitType,
+                    IrStatementOrigin.WHEN
+                )
                 irBlock.statements.add(irSubject)
                 irBlock
             } else {

compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/ClassGenerator.kt

@@ -173,7 +173,7 @@ class ClassGenerator(
         delegatedMembers: List<CallableMemberDescriptor>
     ) {
         val ktDelegateExpression = ktEntry.delegateExpression!!
-        val delegateType = getInferredTypeWithImplicitCastsOrFail(ktDelegateExpression)
+        val delegateType = getTypeInferredByFrontendOrFail(ktDelegateExpression)
         val superType = getOrFail(BindingContext.TYPE, ktEntry.typeReference!!)
         val superTypeConstructorDescriptor = superType.constructor.declarationDescriptor
         val superClass = superTypeConstructorDescriptor as? ClassDescriptor

compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/DelegatedPropertyGenerator.kt

@@ -306,7 +306,7 @@ class DelegatedPropertyGenerator(declarationGenerator: DeclarationGenerator) : D
         return if (provideDelegateResolvedCall != null)
             provideDelegateResolvedCall.resultingDescriptor.returnType!!
         else
-            getInferredTypeWithImplicitCastsOrFail(ktDelegate.expression!!)
+            getTypeInferredByFrontendOrFail(ktDelegate.expression!!)
     }
 
     private fun generateInitializerForLocalDelegatedPropertyDelegate(

compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/ErrorExpressionGenerator.kt

@@ -66,7 +66,7 @@ class ErrorExpressionGenerator(statementGenerator: StatementGenerator) : Stateme
     }
 
     private fun getErrorExpressionType(ktExpression: KtExpression) =
-        getInferredTypeWithImplicitCasts(ktExpression) ?: ErrorUtils.createErrorType("")
+        getTypeInferredByFrontend(ktExpression) ?: ErrorUtils.createErrorType("")
 
     fun generateErrorSimpleName(ktName: KtSimpleNameExpression): IrExpression = generateErrorExpression(ktName) {
         val type = getErrorExpressionType(ktName).toIrType()

compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/Generator.kt

@@ -21,6 +21,7 @@ import org.jetbrains.kotlin.ir.builders.IrGenerator
 import org.jetbrains.kotlin.ir.builders.IrGeneratorWithScope
 import org.jetbrains.kotlin.psi.KtElement
 import org.jetbrains.kotlin.psi.KtExpression
+import org.jetbrains.kotlin.resolve.bindingContextUtil.isUsedAsExpression
 import org.jetbrains.kotlin.resolve.calls.callUtil.getResolvedCall
 import org.jetbrains.kotlin.resolve.calls.model.ResolvedCall
 import org.jetbrains.kotlin.types.KotlinType
@@ -44,11 +45,20 @@ fun <K, V : Any> Generator.getOrFail(slice: ReadOnlySlice<K, V>, key: K): V =
 inline fun <K, V : Any> Generator.getOrFail(slice: ReadOnlySlice<K, V>, key: K, message: (K) -> String): V =
     context.bindingContext[slice, key] ?: throw RuntimeException(message(key))
 
-fun Generator.getInferredTypeWithImplicitCasts(key: KtExpression): KotlinType? =
+fun Generator.getTypeInferredByFrontend(key: KtExpression): KotlinType? =
     context.bindingContext.getType(key)
 
-fun Generator.getInferredTypeWithImplicitCastsOrFail(key: KtExpression): KotlinType =
+fun Generator.getTypeInferredByFrontendOrFail(key: KtExpression): KotlinType =
-    getInferredTypeWithImplicitCasts(key) ?: throw RuntimeException("No type for expression: ${key.text}")
+    getTypeInferredByFrontend(key) ?: throw RuntimeException("No type for expression: ${key.text}")
+
+fun Generator.getExpressionTypeWithCoercionToUnit(key: KtExpression): KotlinType? =
+    if (key.isUsedAsExpression(context.bindingContext))
+        getTypeInferredByFrontend(key)
+    else
+        context.builtIns.unitType
+
+fun Generator.getExpressionTypeWithCoercionToUnitOrFail(key: KtExpression): KotlinType =
+    getExpressionTypeWithCoercionToUnit(key) ?: throw RuntimeException("No type for expression: ${key.text}")
 
 fun Generator.getResolvedCall(key: KtElement): ResolvedCall<out CallableDescriptor>? =
     key.getResolvedCall(context.bindingContext)

compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/LocalClassGenerator.kt

@@ -29,7 +29,7 @@ class LocalClassGenerator(statementGenerator: StatementGenerator) : StatementGen
     fun generateObjectLiteral(ktObjectLiteral: KtObjectLiteralExpression): IrStatement {
         val startOffset = ktObjectLiteral.startOffsetSkippingComments
         val endOffset = ktObjectLiteral.endOffset
-        val objectLiteralType = getInferredTypeWithImplicitCastsOrFail(ktObjectLiteral).toIrType()
+        val objectLiteralType = getTypeInferredByFrontendOrFail(ktObjectLiteral).toIrType()
         val irBlock = IrBlockImpl(startOffset, endOffset, objectLiteralType, IrStatementOrigin.OBJECT_LITERAL)
 
         val irClass = DeclarationGenerator(statementGenerator.context).generateClassOrObjectDeclaration(ktObjectLiteral.objectDeclaration)

compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/LocalFunctionGenerator.kt

@@ -28,7 +28,7 @@ class LocalFunctionGenerator(statementGenerator: StatementGenerator) : Statement
 
     fun generateLambda(ktLambda: KtLambdaExpression): IrStatement {
         val ktFun = ktLambda.functionLiteral
-        val lambdaExpressionType = getInferredTypeWithImplicitCastsOrFail(ktLambda).toIrType()
+        val lambdaExpressionType = getTypeInferredByFrontendOrFail(ktLambda).toIrType()
         val irLambdaFunction = FunctionGenerator(context).generateLambdaFunctionDeclaration(ktFun)
 
         return IrFunctionExpressionImpl(
@@ -43,7 +43,7 @@ class LocalFunctionGenerator(statementGenerator: StatementGenerator) : Statement
         val irFun = generateFunctionDeclaration(ktFun)
         if (ktFun.name != null) return irFun
 
-        val funExpressionType = getInferredTypeWithImplicitCastsOrFail(ktFun).toIrType()
+        val funExpressionType = getTypeInferredByFrontendOrFail(ktFun).toIrType()
         return IrFunctionExpressionImpl(
             ktFun.startOffset, ktFun.endOffset,
             funExpressionType,

compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/ReflectionReferencesGenerator.kt

@@ -37,7 +37,7 @@ class ReflectionReferencesGenerator(statementGenerator: StatementGenerator) : St
     fun generateClassLiteral(ktClassLiteral: KtClassLiteralExpression): IrExpression {
         val ktArgument = ktClassLiteral.receiverExpression!!
         val lhs = getOrFail(BindingContext.DOUBLE_COLON_LHS, ktArgument)
-        val resultType = getInferredTypeWithImplicitCastsOrFail(ktClassLiteral).toIrType()
+        val resultType = getTypeInferredByFrontendOrFail(ktClassLiteral).toIrType()
 
         return if (lhs is DoubleColonLHS.Expression && !lhs.isObjectQualifier) {
             IrGetClassImpl(
@@ -69,7 +69,7 @@ class ReflectionReferencesGenerator(statementGenerator: StatementGenerator) : St
         ).call { dispatchReceiverValue, extensionReceiverValue ->
             generateCallableReference(
                 ktCallableReference,
-                getInferredTypeWithImplicitCastsOrFail(ktCallableReference),
+                getTypeInferredByFrontendOrFail(ktCallableReference),
                 callBuilder.descriptor,
                 callBuilder.typeArguments
             ).also { irCallableReference ->

compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/StatementGenerator.kt

@@ -161,7 +161,7 @@ class StatementGenerator(
         val isBlockBody = expression.parent is KtDeclarationWithBody && expression.parent !is KtFunctionLiteral
         if (isBlockBody) throw AssertionError("Use IrBlockBody and corresponding body generator to generate blocks as function bodies")
 
-        val returnType = getInferredTypeWithImplicitCasts(expression) ?: context.builtIns.unitType
+        val returnType = getExpressionTypeWithCoercionToUnitOrFail(expression)
         val irBlock = IrBlockImpl(expression.startOffsetSkippingComments, expression.endOffset, returnType.toIrType())
 
         expression.statements.forEach {
@@ -226,14 +226,14 @@ class StatementGenerator(
         context.constantValueGenerator.generateConstantValueAsExpression(
             expression.startOffsetSkippingComments,
             expression.endOffset,
-            constant.toConstantValue(getInferredTypeWithImplicitCastsOrFail(expression))
+            constant.toConstantValue(getTypeInferredByFrontendOrFail(expression))
         )
 
     override fun visitStringTemplateExpression(expression: KtStringTemplateExpression, data: Nothing?): IrStatement {
         val startOffset = expression.startOffsetSkippingComments
         val endOffset = expression.endOffset
 
-        val resultType = getInferredTypeWithImplicitCastsOrFail(expression).toIrType()
+        val resultType = getTypeInferredByFrontendOrFail(expression).toIrType()
         val entries = expression.entries.map { it.genExpr() }.postprocessStringTemplateEntries()
 
         return when (entries.size) {

compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/TryCatchExpressionGenerator.kt

@@ -27,7 +27,7 @@ import org.jetbrains.kotlin.resolve.BindingContext
 
 class TryCatchExpressionGenerator(statementGenerator: StatementGenerator) : StatementGeneratorExtension(statementGenerator) {
     fun generateTryCatch(ktTry: KtTryExpression): IrExpression {
-        val resultType = getInferredTypeWithImplicitCastsOrFail(ktTry).toIrType()
+        val resultType = getExpressionTypeWithCoercionToUnitOrFail(ktTry).toIrType()
         val irTryCatch = IrTryImpl(ktTry.startOffsetSkippingComments, ktTry.endOffset, resultType)
 
         irTryCatch.tryResult = ktTry.tryBlock.genExpr()

compiler/testData/ir/irCfg/when/whenReturn.txt

@@ -5,7 +5,7 @@ CONTENT
       1 FUN name:toString visibility:public modality:FINAL <> (grade:kotlin.String) returnType:kotlin.String
       2 GET_VAR 'grade: kotlin.String declared in <root>.toString' type=kotlin.String origin=null
       3 VAR IR_TEMPORARY_VARIABLE name:tmp0_subject type:kotlin.String [val]
-      4 WHEN type=kotlin.Nothing origin=WHEN
+      4 WHEN type=kotlin.Unit origin=WHEN
       5 GET_VAR 'val tmp0_subject: kotlin.String [val] declared in <root>.toString' type=kotlin.String origin=null
       6 CONST String type=kotlin.String value="A"
 OUTGOING -> BB 1, 5

compiler/testData/ir/irText/declarations/parameters/useNextParamInLambda.txt

@@ -23,15 +23,15 @@ FILE fqName:<root> fileName:/useNextParamInLambda.kt
     BLOCK_BODY
       VAR name:result type:kotlin.String [var]
         CONST String type=kotlin.String value="fail"
-      TYPE_OP type=kotlin.Unit origin=IMPLICIT_COERCION_TO_UNIT typeOperand=kotlin.Unit
+      TRY type=kotlin.Unit
-        TRY type=kotlin.Any
+        try: BLOCK type=kotlin.Unit origin=null
-          try: BLOCK type=kotlin.String origin=null
+          TYPE_OP type=kotlin.Unit origin=IMPLICIT_COERCION_TO_UNIT typeOperand=kotlin.Unit
             CALL 'public final fun f (f1: kotlin.Function0<kotlin.String>, f2: kotlin.Function0<kotlin.String>): kotlin.String declared in <root>' type=kotlin.String origin=null
-          CATCH parameter=val e: java.lang.Exception{ kotlin.Exception } [val] declared in <root>.box
+        CATCH parameter=val e: java.lang.Exception{ kotlin.Exception } [val] declared in <root>.box
-            VAR CATCH_PARAMETER name:e type:java.lang.Exception{ kotlin.Exception } [val]
+          VAR CATCH_PARAMETER name:e type:java.lang.Exception{ kotlin.Exception } [val]
-            BLOCK type=kotlin.Unit origin=null
+          BLOCK type=kotlin.Unit origin=null
-              SET_VAR 'var result: kotlin.String [var] declared in <root>.box' type=kotlin.Unit origin=EQ
+            SET_VAR 'var result: kotlin.String [var] declared in <root>.box' type=kotlin.Unit origin=EQ
-                CONST String type=kotlin.String value="OK"
+              CONST String type=kotlin.String value="OK"
       RETURN type=kotlin.Nothing from='public final fun box (): kotlin.String declared in <root>'
         CALL 'public final fun plus (other: kotlin.Any?): kotlin.String declared in kotlin.String' type=kotlin.String origin=PLUS
           $this: CALL 'public final fun f (f1: kotlin.Function0<kotlin.String>, f2: kotlin.Function0<kotlin.String>): kotlin.String declared in <root>' type=kotlin.String origin=null

compiler/testData/ir/irText/expressions/breakContinueInWhen.txt

@@ -23,8 +23,8 @@ FILE fqName:<root> fileName:/breakContinueInWhen.kt
             VAR FOR_LOOP_VARIABLE name:x type:kotlin.Int [val]
               CALL 'public final fun next (): kotlin.Int declared in kotlin.collections.IntIterator' type=kotlin.Int origin=FOR_LOOP_NEXT
                 $this: GET_VAR 'val tmp0_iterator: kotlin.collections.IntIterator [val] declared in <root>.testBreakFor' type=kotlin.collections.IntIterator origin=null
-            BLOCK type=kotlin.Nothing origin=null
+            BLOCK type=kotlin.Unit origin=null
-              WHEN type=kotlin.Nothing origin=WHEN
+              WHEN type=kotlin.Unit origin=WHEN
                 BRANCH
                   if: CALL 'public final fun greater (arg0: kotlin.Int, arg1: kotlin.Int): kotlin.Boolean declared in kotlin.internal.ir' type=kotlin.Boolean origin=GT
                     arg0: GET_VAR 'var k: kotlin.Int [var] declared in <root>.testBreakFor' type=kotlin.Int origin=null
@@ -39,7 +39,7 @@ FILE fqName:<root> fileName:/breakContinueInWhen.kt
           arg0: GET_VAR 'var k: kotlin.Int [var] declared in <root>.testBreakWhile' type=kotlin.Int origin=null
           arg1: CONST Int type=kotlin.Int value=10
         body: BLOCK type=kotlin.Unit origin=null
-          WHEN type=kotlin.Nothing origin=WHEN
+          WHEN type=kotlin.Unit origin=WHEN
             BRANCH
               if: CALL 'public final fun greater (arg0: kotlin.Int, arg1: kotlin.Int): kotlin.Boolean declared in kotlin.internal.ir' type=kotlin.Boolean origin=GT
                 arg0: GET_VAR 'var k: kotlin.Int [var] declared in <root>.testBreakWhile' type=kotlin.Int origin=null
@@ -52,7 +52,7 @@ FILE fqName:<root> fileName:/breakContinueInWhen.kt
       BLOCK type=kotlin.Unit origin=null
         DO_WHILE label=null origin=DO_WHILE_LOOP
           body: COMPOSITE type=kotlin.Unit origin=null
-            WHEN type=kotlin.Nothing origin=WHEN
+            WHEN type=kotlin.Unit origin=WHEN
               BRANCH
                 if: CALL 'public final fun greater (arg0: kotlin.Int, arg1: kotlin.Int): kotlin.Boolean declared in kotlin.internal.ir' type=kotlin.Boolean origin=GT
                   arg0: GET_VAR 'var k: kotlin.Int [var] declared in <root>.testBreakDoWhile' type=kotlin.Int origin=null
@@ -85,8 +85,8 @@ FILE fqName:<root> fileName:/breakContinueInWhen.kt
             VAR FOR_LOOP_VARIABLE name:x type:kotlin.Int [val]
               CALL 'public final fun next (): kotlin.Int declared in kotlin.collections.IntIterator' type=kotlin.Int origin=FOR_LOOP_NEXT
                 $this: GET_VAR 'val tmp0_iterator: kotlin.collections.IntIterator [val] declared in <root>.testContinueFor' type=kotlin.collections.IntIterator origin=null
-            BLOCK type=kotlin.Nothing origin=null
+            BLOCK type=kotlin.Unit origin=null
-              WHEN type=kotlin.Nothing origin=WHEN
+              WHEN type=kotlin.Unit origin=WHEN
                 BRANCH
                   if: CALL 'public final fun greater (arg0: kotlin.Int, arg1: kotlin.Int): kotlin.Boolean declared in kotlin.internal.ir' type=kotlin.Boolean origin=GT
                     arg0: GET_VAR 'var k: kotlin.Int [var] declared in <root>.testContinueFor' type=kotlin.Int origin=null
@@ -101,7 +101,7 @@ FILE fqName:<root> fileName:/breakContinueInWhen.kt
           arg0: GET_VAR 'var k: kotlin.Int [var] declared in <root>.testContinueWhile' type=kotlin.Int origin=null
           arg1: CONST Int type=kotlin.Int value=10
         body: BLOCK type=kotlin.Unit origin=null
-          WHEN type=kotlin.Nothing origin=WHEN
+          WHEN type=kotlin.Unit origin=WHEN
             BRANCH
               if: CALL 'public final fun greater (arg0: kotlin.Int, arg1: kotlin.Int): kotlin.Boolean declared in kotlin.internal.ir' type=kotlin.Boolean origin=GT
                 arg0: GET_VAR 'var k: kotlin.Int [var] declared in <root>.testContinueWhile' type=kotlin.Int origin=null
@@ -122,7 +122,7 @@ FILE fqName:<root> fileName:/breakContinueInWhen.kt
                   CALL 'public final fun inc (): kotlin.Int declared in kotlin.Int' type=kotlin.Int origin=PREFIX_INCR
                     $this: GET_VAR 'var k: kotlin.Int [var] declared in <root>.testContinueDoWhile' type=kotlin.Int origin=PREFIX_INCR
                 GET_VAR 'var k: kotlin.Int [var] declared in <root>.testContinueDoWhile' type=kotlin.Int origin=PREFIX_INCR
-            WHEN type=kotlin.Nothing origin=WHEN
+            WHEN type=kotlin.Unit origin=WHEN
               BRANCH
                 if: CALL 'public final fun greater (arg0: kotlin.Int, arg1: kotlin.Int): kotlin.Boolean declared in kotlin.internal.ir' type=kotlin.Boolean origin=GT
                   arg0: GET_VAR 'var k: kotlin.Int [var] declared in <root>.testContinueDoWhile' type=kotlin.Int origin=null

compiler/testData/ir/irText/expressions/catchParameterAccess.txt

@@ -9,6 +9,6 @@ FILE fqName:<root> fileName:/catchParameterAccess.kt
               $this: GET_VAR 'f: kotlin.Function0<kotlin.Unit> declared in <root>.test' type=kotlin.Function0<kotlin.Unit> origin=VARIABLE_AS_FUNCTION
           CATCH parameter=val e: java.lang.Exception{ kotlin.Exception } [val] declared in <root>.test
             VAR CATCH_PARAMETER name:e type:java.lang.Exception{ kotlin.Exception } [val]
-            BLOCK type=kotlin.Nothing origin=null
+            BLOCK type=kotlin.Unit origin=null
               THROW type=kotlin.Nothing
                 GET_VAR 'val e: java.lang.Exception{ kotlin.Exception } [val] declared in <root>.test' type=java.lang.Exception{ kotlin.Exception } origin=null

compiler/testData/ir/irText/expressions/forWithBreakContinue.txt

@@ -13,7 +13,7 @@ FILE fqName:<root> fileName:/forWithBreakContinue.kt
             VAR FOR_LOOP_VARIABLE name:s type:kotlin.String [val]
               CALL 'public abstract fun next (): T of kotlin.collections.Iterator declared in kotlin.collections.Iterator' type=kotlin.String origin=FOR_LOOP_NEXT
                 $this: GET_VAR 'val tmp0_iterator: kotlin.collections.Iterator<kotlin.String> [val] declared in <root>.testForBreak1' type=kotlin.collections.Iterator<kotlin.String> origin=null
-            BLOCK type=kotlin.Nothing origin=null
+            BLOCK type=kotlin.Unit origin=null
               BREAK label=null loop.label=null
   FUN name:testForBreak2 visibility:public modality:FINAL <> (ss:kotlin.collections.List<kotlin.String>) returnType:kotlin.Unit
     VALUE_PARAMETER name:ss index:0 type:kotlin.collections.List<kotlin.String>
@@ -29,7 +29,7 @@ FILE fqName:<root> fileName:/forWithBreakContinue.kt
             VAR FOR_LOOP_VARIABLE name:s1 type:kotlin.String [val]
               CALL 'public abstract fun next (): T of kotlin.collections.Iterator declared in kotlin.collections.Iterator' type=kotlin.String origin=FOR_LOOP_NEXT
                 $this: GET_VAR 'val tmp0_iterator: kotlin.collections.Iterator<kotlin.String> [val] declared in <root>.testForBreak2' type=kotlin.collections.Iterator<kotlin.String> origin=null
-            BLOCK type=kotlin.Nothing origin=null
+            BLOCK type=kotlin.Unit origin=null
               BLOCK type=kotlin.Unit origin=FOR_LOOP
                 VAR FOR_LOOP_ITERATOR name:tmp1_iterator type:kotlin.collections.Iterator<kotlin.String> [val]
                   CALL 'public abstract fun iterator (): kotlin.collections.Iterator<E of kotlin.collections.List> declared in kotlin.collections.List' type=kotlin.collections.Iterator<kotlin.String> origin=FOR_LOOP_ITERATOR
@@ -41,7 +41,7 @@ FILE fqName:<root> fileName:/forWithBreakContinue.kt
                     VAR FOR_LOOP_VARIABLE name:s2 type:kotlin.String [val]
                       CALL 'public abstract fun next (): T of kotlin.collections.Iterator declared in kotlin.collections.Iterator' type=kotlin.String origin=FOR_LOOP_NEXT
                         $this: GET_VAR 'val tmp1_iterator: kotlin.collections.Iterator<kotlin.String> [val] declared in <root>.testForBreak2' type=kotlin.collections.Iterator<kotlin.String> origin=null
-                    BLOCK type=kotlin.Nothing origin=null
+                    BLOCK type=kotlin.Unit origin=null
                       BREAK label=OUTER loop.label=OUTER
                       BREAK label=INNER loop.label=INNER
                       BREAK label=null loop.label=INNER
@@ -60,7 +60,7 @@ FILE fqName:<root> fileName:/forWithBreakContinue.kt
             VAR FOR_LOOP_VARIABLE name:s type:kotlin.String [val]
               CALL 'public abstract fun next (): T of kotlin.collections.Iterator declared in kotlin.collections.Iterator' type=kotlin.String origin=FOR_LOOP_NEXT
                 $this: GET_VAR 'val tmp0_iterator: kotlin.collections.Iterator<kotlin.String> [val] declared in <root>.testForContinue1' type=kotlin.collections.Iterator<kotlin.String> origin=null
-            BLOCK type=kotlin.Nothing origin=null
+            BLOCK type=kotlin.Unit origin=null
               CONTINUE label=null loop.label=null
   FUN name:testForContinue2 visibility:public modality:FINAL <> (ss:kotlin.collections.List<kotlin.String>) returnType:kotlin.Unit
     VALUE_PARAMETER name:ss index:0 type:kotlin.collections.List<kotlin.String>
@@ -76,7 +76,7 @@ FILE fqName:<root> fileName:/forWithBreakContinue.kt
             VAR FOR_LOOP_VARIABLE name:s1 type:kotlin.String [val]
               CALL 'public abstract fun next (): T of kotlin.collections.Iterator declared in kotlin.collections.Iterator' type=kotlin.String origin=FOR_LOOP_NEXT
                 $this: GET_VAR 'val tmp0_iterator: kotlin.collections.Iterator<kotlin.String> [val] declared in <root>.testForContinue2' type=kotlin.collections.Iterator<kotlin.String> origin=null
-            BLOCK type=kotlin.Nothing origin=null
+            BLOCK type=kotlin.Unit origin=null
               BLOCK type=kotlin.Unit origin=FOR_LOOP
                 VAR FOR_LOOP_ITERATOR name:tmp1_iterator type:kotlin.collections.Iterator<kotlin.String> [val]
                   CALL 'public abstract fun iterator (): kotlin.collections.Iterator<E of kotlin.collections.List> declared in kotlin.collections.List' type=kotlin.collections.Iterator<kotlin.String> origin=FOR_LOOP_ITERATOR
@@ -88,7 +88,7 @@ FILE fqName:<root> fileName:/forWithBreakContinue.kt
                     VAR FOR_LOOP_VARIABLE name:s2 type:kotlin.String [val]
                       CALL 'public abstract fun next (): T of kotlin.collections.Iterator declared in kotlin.collections.Iterator' type=kotlin.String origin=FOR_LOOP_NEXT
                         $this: GET_VAR 'val tmp1_iterator: kotlin.collections.Iterator<kotlin.String> [val] declared in <root>.testForContinue2' type=kotlin.collections.Iterator<kotlin.String> origin=null
-                    BLOCK type=kotlin.Nothing origin=null
+                    BLOCK type=kotlin.Unit origin=null
                       CONTINUE label=OUTER loop.label=OUTER
                       CONTINUE label=INNER loop.label=INNER
                       CONTINUE label=null loop.label=INNER

compiler/testData/ir/irText/expressions/ifElseIf.txt

@@ -36,22 +36,22 @@ FILE fqName:<root> fileName:/ifElseIf.kt
   FUN name:testEmptyBranches2 visibility:public modality:FINAL <> (flag:kotlin.Boolean) returnType:kotlin.Unit
     VALUE_PARAMETER name:flag index:0 type:kotlin.Boolean
     BLOCK_BODY
-      TYPE_OP type=kotlin.Unit origin=IMPLICIT_COERCION_TO_UNIT typeOperand=kotlin.Unit
+      WHEN type=kotlin.Unit origin=IF
-        WHEN type=kotlin.Any origin=IF
+        BRANCH
-          BRANCH
+          if: GET_VAR 'flag: kotlin.Boolean declared in <root>.testEmptyBranches2' type=kotlin.Boolean origin=null
-            if: GET_VAR 'flag: kotlin.Boolean declared in <root>.testEmptyBranches2' type=kotlin.Boolean origin=null
+          then: BLOCK type=kotlin.Unit origin=null
-            then: BLOCK type=kotlin.Unit origin=null
+        BRANCH
-          BRANCH
+          if: CONST Boolean type=kotlin.Boolean value=true
-            if: CONST Boolean type=kotlin.Boolean value=true
+          then: TYPE_OP type=kotlin.Unit origin=IMPLICIT_COERCION_TO_UNIT typeOperand=kotlin.Unit
-            then: CONST Boolean type=kotlin.Boolean value=true
+            CONST Boolean type=kotlin.Boolean value=true
-      TYPE_OP type=kotlin.Unit origin=IMPLICIT_COERCION_TO_UNIT typeOperand=kotlin.Unit
+      WHEN type=kotlin.Unit origin=IF
-        WHEN type=kotlin.Any origin=IF
+        BRANCH
-          BRANCH
+          if: GET_VAR 'flag: kotlin.Boolean declared in <root>.testEmptyBranches2' type=kotlin.Boolean origin=null
-            if: GET_VAR 'flag: kotlin.Boolean declared in <root>.testEmptyBranches2' type=kotlin.Boolean origin=null
+          then: TYPE_OP type=kotlin.Unit origin=IMPLICIT_COERCION_TO_UNIT typeOperand=kotlin.Unit
-            then: CONST Boolean type=kotlin.Boolean value=true
+            CONST Boolean type=kotlin.Boolean value=true
-          BRANCH
+        BRANCH
-            if: CONST Boolean type=kotlin.Boolean value=true
+          if: CONST Boolean type=kotlin.Boolean value=true
-            then: BLOCK type=kotlin.Unit origin=null
+          then: BLOCK type=kotlin.Unit origin=null
   FUN name:testEmptyBranches3 visibility:public modality:FINAL <> (flag:kotlin.Boolean) returnType:kotlin.Unit
     VALUE_PARAMETER name:flag index:0 type:kotlin.Boolean
     BLOCK_BODY

compiler/testData/ir/irText/expressions/throw.txt

@@ -10,7 +10,7 @@ FILE fqName:<root> fileName:/throw.kt
         BRANCH
           if: TYPE_OP type=kotlin.Boolean origin=INSTANCEOF typeOperand=kotlin.Throwable
             GET_VAR 'a: kotlin.Any declared in <root>.testImplicitCast' type=kotlin.Any origin=null
-          then: BLOCK type=kotlin.Nothing origin=null
+          then: BLOCK type=kotlin.Unit origin=null
             THROW type=kotlin.Nothing
               TYPE_OP type=kotlin.Throwable origin=IMPLICIT_CAST typeOperand=kotlin.Throwable
                 GET_VAR 'a: kotlin.Any declared in <root>.testImplicitCast' type=kotlin.Any origin=null

compiler/testData/ir/irText/expressions/tryCatch.txt

@@ -22,7 +22,7 @@ FILE fqName:<root> fileName:/tryCatch.kt
             BLOCK type=kotlin.Int origin=null
               CALL 'public final fun println (): kotlin.Unit [inline] declared in kotlin.io' type=kotlin.Unit origin=null
               CONST Int type=kotlin.Int value=24
-          finally: TYPE_OP type=kotlin.Unit origin=IMPLICIT_COERCION_TO_UNIT typeOperand=kotlin.Unit
+          finally: BLOCK type=kotlin.Unit origin=null
-            BLOCK type=kotlin.Int origin=null
+            CALL 'public final fun println (): kotlin.Unit [inline] declared in kotlin.io' type=kotlin.Unit origin=null
-              CALL 'public final fun println (): kotlin.Unit [inline] declared in kotlin.io' type=kotlin.Unit origin=null
+            TYPE_OP type=kotlin.Unit origin=IMPLICIT_COERCION_TO_UNIT typeOperand=kotlin.Unit
               CONST Int type=kotlin.Int value=555

compiler/testData/ir/irText/expressions/whenReturn.txt

@@ -2,10 +2,10 @@ FILE fqName:<root> fileName:/whenReturn.kt
   FUN name:toString visibility:public modality:FINAL <> (grade:kotlin.String) returnType:kotlin.String
     VALUE_PARAMETER name:grade index:0 type:kotlin.String
     BLOCK_BODY
-      BLOCK type=kotlin.Nothing origin=WHEN
+      BLOCK type=kotlin.Unit origin=WHEN
         VAR IR_TEMPORARY_VARIABLE name:tmp0_subject type:kotlin.String [val]
           GET_VAR 'grade: kotlin.String declared in <root>.toString' type=kotlin.String origin=null
-        WHEN type=kotlin.Nothing origin=WHEN
+        WHEN type=kotlin.Unit origin=WHEN
           BRANCH
             if: CALL 'public final fun EQEQ (arg0: kotlin.Any?, arg1: kotlin.Any?): kotlin.Boolean declared in kotlin.internal.ir' type=kotlin.Boolean origin=EQEQ
               arg0: GET_VAR 'val tmp0_subject: kotlin.String [val] declared in <root>.toString' type=kotlin.String origin=null

compiler/testData/ir/irText/expressions/whenReturnUnit.txt

@@ -10,10 +10,10 @@ FILE fqName:<root> fileName:/whenReturnUnit.kt
           block: FUN_EXPR type=kotlin.Function0<kotlin.Unit> origin=LAMBDA
             FUN LOCAL_FUNCTION_FOR_LAMBDA name:<anonymous> visibility:local modality:FINAL <> () returnType:kotlin.Unit
               BLOCK_BODY
-                BLOCK type=kotlin.Nothing origin=WHEN
+                BLOCK type=kotlin.Unit origin=WHEN
                   VAR IR_TEMPORARY_VARIABLE name:tmp0_subject type:kotlin.Int [val]
                     GET_VAR 'x: kotlin.Int declared in <root>.branch' type=kotlin.Int origin=null
-                  WHEN type=kotlin.Nothing origin=WHEN
+                  WHEN type=kotlin.Unit origin=WHEN
                     BRANCH
                       if: CALL 'public final fun EQEQ (arg0: kotlin.Any?, arg1: kotlin.Any?): kotlin.Boolean declared in kotlin.internal.ir' type=kotlin.Boolean origin=EQEQ
                         arg0: GET_VAR 'val tmp0_subject: kotlin.Int [val] declared in <root>.branch.<anonymous>' type=kotlin.Int origin=null

compiler/testData/ir/irText/expressions/whenUnusedExpression.txt

@@ -3,23 +3,25 @@ FILE fqName:<root> fileName:/whenUnusedExpression.kt
     VALUE_PARAMETER name:b index:0 type:kotlin.Boolean
     VALUE_PARAMETER name:i index:1 type:kotlin.Int
     BLOCK_BODY
-      TYPE_OP type=kotlin.Unit origin=IMPLICIT_COERCION_TO_UNIT typeOperand=kotlin.Unit
+      WHEN type=kotlin.Unit origin=IF
-        WHEN type=kotlin.Int? origin=IF
+        BRANCH
-          BRANCH
+          if: GET_VAR 'b: kotlin.Boolean declared in <root>.test' type=kotlin.Boolean origin=null
-            if: GET_VAR 'b: kotlin.Boolean declared in <root>.test' type=kotlin.Boolean origin=null
+          then: BLOCK type=kotlin.Unit origin=null
-            then: BLOCK type=kotlin.Int? origin=null
+            BLOCK type=kotlin.Unit origin=WHEN
-              BLOCK type=kotlin.Int? origin=WHEN
+              VAR IR_TEMPORARY_VARIABLE name:tmp0_subject type:kotlin.Int [val]
-                VAR IR_TEMPORARY_VARIABLE name:tmp0_subject type:kotlin.Int [val]
+                GET_VAR 'i: kotlin.Int declared in <root>.test' type=kotlin.Int origin=null
-                  GET_VAR 'i: kotlin.Int declared in <root>.test' type=kotlin.Int origin=null
+              WHEN type=kotlin.Unit origin=WHEN
-                WHEN type=kotlin.Int? origin=WHEN
+                BRANCH
-                  BRANCH
+                  if: CALL 'public final fun EQEQ (arg0: kotlin.Any?, arg1: kotlin.Any?): kotlin.Boolean declared in kotlin.internal.ir' type=kotlin.Boolean origin=EQEQ
-                    if: CALL 'public final fun EQEQ (arg0: kotlin.Any?, arg1: kotlin.Any?): kotlin.Boolean declared in kotlin.internal.ir' type=kotlin.Boolean origin=EQEQ
+                    arg0: GET_VAR 'val tmp0_subject: kotlin.Int [val] declared in <root>.test' type=kotlin.Int origin=null
-                      arg0: GET_VAR 'val tmp0_subject: kotlin.Int [val] declared in <root>.test' type=kotlin.Int origin=null
+                    arg1: CONST Int type=kotlin.Int value=0
-                      arg1: CONST Int type=kotlin.Int value=0
+                  then: TYPE_OP type=kotlin.Unit origin=IMPLICIT_COERCION_TO_UNIT typeOperand=kotlin.Unit
-                    then: CONST Int type=kotlin.Int value=1
+                    CONST Int type=kotlin.Int value=1
-                  BRANCH
+                BRANCH
-                    if: CONST Boolean type=kotlin.Boolean value=true
+                  if: CONST Boolean type=kotlin.Boolean value=true
-                    then: CONST Null type=kotlin.Nothing? value=null
+                  then: TYPE_OP type=kotlin.Unit origin=IMPLICIT_COERCION_TO_UNIT typeOperand=kotlin.Unit
-          BRANCH
+                    CONST Null type=kotlin.Nothing? value=null
-            if: CONST Boolean type=kotlin.Boolean value=true
+        BRANCH
-            then: CONST Null type=kotlin.Nothing? value=null
+          if: CONST Boolean type=kotlin.Boolean value=true
+          then: TYPE_OP type=kotlin.Unit origin=IMPLICIT_COERCION_TO_UNIT typeOperand=kotlin.Unit
+            CONST Null type=kotlin.Nothing? value=null

compiler/testData/ir/irText/regressions/kt24114.txt

@@ -12,19 +12,19 @@ FILE fqName:<root> fileName:/kt24114.kt
       WHILE label=null origin=WHILE_LOOP
         condition: CONST Boolean type=kotlin.Boolean value=true
         body: BLOCK type=kotlin.Unit origin=null
-          BLOCK type=kotlin.Nothing origin=WHEN
+          BLOCK type=kotlin.Unit origin=WHEN
             VAR IR_TEMPORARY_VARIABLE name:tmp0_subject type:kotlin.Int [val]
               CALL 'public final fun one (): kotlin.Int declared in <root>' type=kotlin.Int origin=null
-            WHEN type=kotlin.Nothing origin=WHEN
+            WHEN type=kotlin.Unit origin=WHEN
               BRANCH
                 if: CALL 'public final fun EQEQ (arg0: kotlin.Any?, arg1: kotlin.Any?): kotlin.Boolean declared in kotlin.internal.ir' type=kotlin.Boolean origin=EQEQ
                   arg0: GET_VAR 'val tmp0_subject: kotlin.Int [val] declared in <root>.test1' type=kotlin.Int origin=null
                   arg1: CONST Int type=kotlin.Int value=1
-                then: BLOCK type=kotlin.Nothing origin=null
+                then: BLOCK type=kotlin.Unit origin=null
-                  BLOCK type=kotlin.Nothing origin=WHEN
+                  BLOCK type=kotlin.Unit origin=WHEN
                     VAR IR_TEMPORARY_VARIABLE name:tmp1_subject type:kotlin.Int [val]
                       CALL 'public final fun two (): kotlin.Int declared in <root>' type=kotlin.Int origin=null
-                    WHEN type=kotlin.Nothing origin=WHEN
+                    WHEN type=kotlin.Unit origin=WHEN
                       BRANCH
                         if: CALL 'public final fun EQEQ (arg0: kotlin.Any?, arg1: kotlin.Any?): kotlin.Boolean declared in kotlin.internal.ir' type=kotlin.Boolean origin=EQEQ
                           arg0: GET_VAR 'val tmp1_subject: kotlin.Int [val] declared in <root>.test1' type=kotlin.Int origin=null
@@ -40,18 +40,18 @@ FILE fqName:<root> fileName:/kt24114.kt
       WHILE label=null origin=WHILE_LOOP
         condition: CONST Boolean type=kotlin.Boolean value=true
         body: BLOCK type=kotlin.Unit origin=null
-          BLOCK type=kotlin.Nothing origin=WHEN
+          BLOCK type=kotlin.Unit origin=WHEN
             VAR IR_TEMPORARY_VARIABLE name:tmp0_subject type:kotlin.Int [val]
               CALL 'public final fun one (): kotlin.Int declared in <root>' type=kotlin.Int origin=null
-            WHEN type=kotlin.Nothing origin=WHEN
+            WHEN type=kotlin.Unit origin=WHEN
               BRANCH
                 if: CALL 'public final fun EQEQ (arg0: kotlin.Any?, arg1: kotlin.Any?): kotlin.Boolean declared in kotlin.internal.ir' type=kotlin.Boolean origin=EQEQ
                   arg0: GET_VAR 'val tmp0_subject: kotlin.Int [val] declared in <root>.test2' type=kotlin.Int origin=null
                   arg1: CONST Int type=kotlin.Int value=1
-                then: BLOCK type=kotlin.Nothing origin=WHEN
+                then: BLOCK type=kotlin.Unit origin=WHEN
                   VAR IR_TEMPORARY_VARIABLE name:tmp1_subject type:kotlin.Int [val]
                     CALL 'public final fun two (): kotlin.Int declared in <root>' type=kotlin.Int origin=null
-                  WHEN type=kotlin.Nothing origin=WHEN
+                  WHEN type=kotlin.Unit origin=WHEN
                     BRANCH
                       if: CALL 'public final fun EQEQ (arg0: kotlin.Any?, arg1: kotlin.Any?): kotlin.Boolean declared in kotlin.internal.ir' type=kotlin.Boolean origin=EQEQ
                         arg0: GET_VAR 'val tmp1_subject: kotlin.Int [val] declared in <root>.test2' type=kotlin.Int origin=null