JVM IR: Don't produce CHECKCASTs on null constants (KT-36650)

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

@@ -718,7 +718,7 @@ class ExpressionCodegen(
             is Float -> mv.fconst(value)
             is Double -> mv.dconst(value)
             is Number -> mv.iconst(value.toInt())
-            else -> mv.aconst(value)
+            else -> if (expression.kind == IrConstKind.Null) return nullConstant else mv.aconst(value)
         }
         return expression.onStack
     }

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

@@ -13,6 +13,7 @@ import org.jetbrains.kotlin.codegen.AsmUtil
 import org.jetbrains.kotlin.codegen.StackValue
 import org.jetbrains.kotlin.ir.types.*
 import org.jetbrains.kotlin.ir.util.parentAsClass
+import org.jetbrains.kotlin.resolve.jvm.AsmTypes
 import org.jetbrains.kotlin.types.KotlinType
 import org.jetbrains.org.objectweb.asm.Label
 import org.jetbrains.org.objectweb.asm.Type
@@ -162,3 +163,12 @@ val IrType.unboxed: IrType
 // A Non-materialized value of Unit type that is only materialized through coercion.
 val ExpressionCodegen.unitValue: PromisedValue
     get() = MaterialValue(this, Type.VOID_TYPE, context.irBuiltIns.unitType)
+
+val ExpressionCodegen.nullConstant: PromisedValue
+    get() = object : PromisedValue(this, AsmTypes.OBJECT_TYPE, context.irBuiltIns.nothingNType) {
+        override fun materializeAt(target: Type, irTarget: IrType) {
+            mv.aconst(null)
+        }
+
+        override fun discard() {}
+    }

compiler/testData/codegen/box/classes/kt1018.kt

@@ -1,3 +1,6 @@
+// IGNORE_BACKEND_FIR: JVM_IR
+// The IR prduced by FIR implicitly casts `null` of type `Nothing?` to type `Int` instead of `Int?` in `getColumnCount`.
+
 public class StockMarketTableModel() {
 
     public fun getColumnCount() : Int {

compiler/testData/codegen/box/coroutines/tailCallOptimizations/crossinline_ir.txt

@@ -2,7 +2,6 @@
 @kotlin.coroutines.jvm.internal.DebugMetadata
 public final class CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1$1 {
     field L$0: java.lang.Object
-    field L$1: java.lang.Object
     field label: int
     synthetic field result: java.lang.Object
     synthetic final field this$0: CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1
@@ -98,7 +97,6 @@ public final class CrossinlineKt$consumeEach$2 {
 @kotlin.coroutines.jvm.internal.DebugMetadata
 public final class CrossinlineKt$filter$$inlined$source$1$1 {
     field L$0: java.lang.Object
-    field L$1: java.lang.Object
     field label: int
     synthetic field result: java.lang.Object
     synthetic final field this$0: CrossinlineKt$filter$$inlined$source$1
@@ -190,7 +188,6 @@ public final class CrossinlineKt$range$$inlined$source$1$1 {
     field I$1: int
     field L$0: java.lang.Object
     field L$1: java.lang.Object
-    field L$2: java.lang.Object
     field label: int
     synthetic field result: java.lang.Object
     synthetic final field this$0: CrossinlineKt$range$$inlined$source$1
@@ -216,7 +213,6 @@ public final class CrossinlineKt$range$$inlined$source$1 {
 public final class CrossinlineKt$source$1$consume$1 {
     // source: 'crossinline.kt'
     field L$0: java.lang.Object
-    field L$1: java.lang.Object
     field label: int
     synthetic field result: java.lang.Object
     synthetic final field this$0: CrossinlineKt$source$1

compiler/testData/codegen/bytecodeText/checkcast/kt15411.kt

@@ -1,7 +1,3 @@
-// IGNORE_BACKEND: JVM_IR
-// TODO KT-36650 Don't generate CHECKCAST on null values in JVM_IR
-// KT-15411 Unnecessary CHECKCAST bytecode when dealing with null
-
 fun test1(): String? {
     return null
 }

compiler/testData/codegen/bytecodeText/coercionToUnitOptimization/safeLet.kt

@@ -16,14 +16,12 @@ fun test(ss: List<String?>) {
     }
 }
 
-// JVM_TEMPLATES
-// 2 POP
 // 0 INVOKESTATIC java/lang/Boolean\.valueOf
 // 0 CHECKCAST java/lang/Boolean
 // 0 ACONST_NULL
 
-// JVM_IR_TEMPLATES
+// JVM_TEMPLATES
 // 2 POP
-// 0 INVOKESTATIC java/lang/Boolean\.valueOf
-// 1 CHECKCAST java/lang/Boolean
-// 1 ACONST_NULL
+
+// JVM_IR_TEMPLATES
+// 1 POP

compiler/testData/codegen/bytecodeText/coroutines/cleanup/nullCleanup.kt

@@ -12,6 +12,12 @@ suspend fun test() {
     blackhole(a)
 }
 
-// jsut before suspension point
+// 2 PUTFIELD .*L\$0 : Ljava/lang/Object;
+
+// JVM_TEMPLATES:
+// just before suspension point
 // 1 ACONST_NULL
-// 2 PUTFIELD .*L\$0 : Ljava/lang/Object;
+
+// JVM_IR_TEMPLATES:
+// two stores to initialize the `a` variable and one null constant to store in the spill slot.
+// 3 ACONST_NULL