[IR][Native] Remove redundant implicit casts

^KT-80953

Author: vsukharev

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

@@ -0,0 +1,35 @@
+/*
+ * Copyright 2010-2025 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.backend.common.lower
+
+import org.jetbrains.kotlin.backend.common.FileLoweringPass
+import org.jetbrains.kotlin.backend.common.LoweringContext
+import org.jetbrains.kotlin.ir.declarations.IrFile
+import org.jetbrains.kotlin.ir.expressions.IrExpression
+import org.jetbrains.kotlin.ir.expressions.IrTypeOperator
+import org.jetbrains.kotlin.ir.expressions.IrTypeOperatorCall
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformerVoid
+import org.jetbrains.kotlin.ir.visitors.transformChildrenVoid
+
+/**
+ * Removes redundant casts like
+ * - `TYPE_OP type=kotlin.Int origin=IMPLICIT_CAST typeOperand=kotlin.Int`
+ */
+class RedundantCastsRemoverLowering(val context: LoweringContext) : FileLoweringPass {
+    override fun lower(irFile: IrFile) {
+        irFile.transformChildrenVoid(Transformer())
+    }
+
+    private class Transformer : IrElementTransformerVoid() {
+        override fun visitTypeOperator(expression: IrTypeOperatorCall): IrExpression {
+            if (expression.operator == IrTypeOperator.IMPLICIT_CAST && expression.type == expression.argument.type) {
+                // Replace a redundant implicit cast with its argument
+                return super.visitExpression(expression.argument)
+            }
+            return super.visitTypeOperator(expression)
+        }
+    }
+}

kotlin-native/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/driver/phases/NativeLoweringPhases.kt

@@ -557,6 +557,12 @@ private val assertionRemoverPhase = createFileLoweringPhase(
         prerequisite = setOf(assertionWrapperPhase),
 )
 
+internal val redundantCastsRemoverPhase = createFileLoweringPhase(
+        lowering = ::RedundantCastsRemoverLowering,
+        name = "RedundantCastsRemoverLowering",
+        prerequisite = setOf(inlineAllFunctionsPhase),
+)
+
 internal val constEvaluationPhase = createFileLoweringPhase(
         lowering = { context: Context ->
             val configuration = IrInterpreterConfiguration(printOnlyExceptionMessage = true)

kotlin-native/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/driver/phases/TopLevelPhases.kt

@@ -163,7 +163,7 @@ internal fun <C : NativeBackendPhaseContext> PhaseEngine<C>.runBackend(backendCo
                 fragmentWithState.forEach { (fragment, state) -> state.runSpecifiedLowerings(fragment, getLoweringsUpToAndIncludingSyntheticAccessors()) }
                 fragmentWithState.forEach { (fragment, state) -> state.runSpecifiedLowerings(fragment, validateIrAfterInliningOnlyPrivateFunctions) }
                 fragmentWithState.forEach { (fragment, state) -> state.runSpecifiedLowerings(fragment, listOf(inlineAllFunctionsPhase)) }
-                fragmentWithState.forEach { (fragment, state) -> state.runSpecifiedLowerings(fragment, listOf(specialObjCValidationPhase)) }
+                fragmentWithState.forEach { (fragment, state) -> state.runSpecifiedLowerings(fragment, listOf(specialObjCValidationPhase, redundantCastsRemoverPhase)) }
             }
 
             fragmentWithState.forEach { (fragment, state) -> state.runSpecifiedLowerings(fragment, validateIrAfterInliningAllFunctions) }