JVM IR: Avoid CHECKCASTs on type operators (KT-39520)

The type information coming from Java or Kotlin generics may be wrong
due to type erasure and a CHECKCAST instruction could throw an
exception.

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/TypeOperatorLowering.kt

@@ -58,7 +58,7 @@ private class TypeOperatorLowering(private val context: JvmBackendContext) : Fil
             type.isReifiedTypeParameter ->
                 irIs(argument, type)
             argument.type.isNullable() && type.isNullable() -> {
-                irLetS(argument) { valueSymbol ->
+                irLetS(argument, irType = context.irBuiltIns.anyNType) { valueSymbol ->
                     context.oror(
                         irEqualsNull(irGet(valueSymbol.owner)),
                         irIs(irGet(valueSymbol.owner), type.makeNotNull())
@@ -76,7 +76,7 @@ private class TypeOperatorLowering(private val context: JvmBackendContext) : Fil
             builder.irAs(argument, type)
         argument.type.isNullable() && !type.isNullable() ->
             with(builder) {
-                irLetS(argument) { valueSymbol ->
+                irLetS(argument, irType = context.irBuiltIns.anyNType) { valueSymbol ->
                     irIfNull(
                         type,
                         irGet(valueSymbol.owner),
@@ -118,7 +118,11 @@ private class TypeOperatorLowering(private val context: JvmBackendContext) : Fil
                     expression.transformChildrenVoid()
                     expression
                 } else {
-                    irLetS(expression.argument.transformVoid(), IrStatementOrigin.SAFE_CALL) { valueSymbol ->
+                    irLetS(
+                        expression.argument.transformVoid(),
+                        IrStatementOrigin.SAFE_CALL,
+                        irType = context.irBuiltIns.anyNType
+                    ) { valueSymbol ->
                         irIfThenElse(
                             expression.type,
                             lowerInstanceOf(irGet(valueSymbol.owner), expression.typeOperand.makeNotNull()),
@@ -138,7 +142,7 @@ private class TypeOperatorLowering(private val context: JvmBackendContext) : Fil
                 val (startOffset, endOffset) = expression.extents()
                 val source = sourceViewFor(parent as IrDeclaration).subSequence(startOffset, endOffset).toString()
 
-                fun checkExpressionValue(valueSymbol: IrValueSymbol): IrExpression =
+                irLetS(expression.argument.transformVoid(), irType = context.irBuiltIns.anyNType) { valueSymbol ->
                     irComposite(resultType = expression.type) {
                         +irCall(checkExpressionValueIsNotNull).apply {
                             putValueArgument(0, irGet(valueSymbol.owner))
@@ -146,14 +150,6 @@ private class TypeOperatorLowering(private val context: JvmBackendContext) : Fil
                         }
                         +irGet(valueSymbol.owner)
                     }
-
-                val argument = expression.argument.transformVoid()
-                if (argument is IrGetValue) {
-                    checkExpressionValue(argument.symbol)
-                } else {
-                    irLetS(argument) { valueSymbol ->
-                        checkExpressionValue(valueSymbol)
-                    }
                 }
             }
 

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/builders/ExpressionHelpers.kt

@@ -12,6 +12,7 @@ import org.jetbrains.kotlin.ir.expressions.*
 import org.jetbrains.kotlin.ir.expressions.impl.*
 import org.jetbrains.kotlin.ir.symbols.*
 import org.jetbrains.kotlin.ir.types.IrType
+import org.jetbrains.kotlin.ir.util.isImmutable
 import org.jetbrains.kotlin.ir.util.parentAsClass
 import org.jetbrains.kotlin.ir.util.render
 import org.jetbrains.kotlin.types.KotlinType
@@ -23,14 +24,23 @@ inline fun IrBuilderWithScope.irLetS(
     value: IrExpression,
     origin: IrStatementOrigin? = null,
     nameHint: String? = null,
+    irType: IrType? = null,
     body: (IrValueSymbol) -> IrExpression
 ): IrExpression {
-    val irTemporary = scope.createTemporaryVariable(value, nameHint)
-    val irResult = body(irTemporary.symbol)
-    val irBlock = IrBlockImpl(startOffset, endOffset, irResult.type, origin)
-    irBlock.statements.add(irTemporary)
-    irBlock.statements.add(irResult)
-    return irBlock
+    val (valueSymbol, irTemporary) = if (value is IrGetValue && value.symbol.owner.isImmutable) {
+        value.symbol to null
+    } else {
+        scope.createTemporaryVariable(value, nameHint, irType = irType).let { it.symbol to it }
+    }
+    val irResult = body(valueSymbol)
+    return if (irTemporary == null) {
+        irResult
+    } else {
+        val irBlock = IrBlockImpl(startOffset, endOffset, irResult.type, origin)
+        irBlock.statements.add(irTemporary)
+        irBlock.statements.add(irResult)
+        irBlock
+    }
 }