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

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