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

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