FIR DFA: x !is T? => x != null

^KT-22996 tag fixed-in-k2

compiler/testData/diagnostics/tests/infos/SmartCasts.fir.kt

@@ -58,7 +58,7 @@ fun f11(a : A?) {
     is A -> a.foo()
     is Any -> a.foo()
     <!USELESS_IS_CHECK!>is Any?<!> -> a.<!UNRESOLVED_REFERENCE!>bar<!>()
-    else -> a?.foo()
+    else -> a<!UNNECESSARY_SAFE_CALL!>?.<!>foo()
   }
 }
 
@@ -68,8 +68,8 @@ fun f12(a : A?) {
     is A -> a.foo()
     is Any -> a.foo();
     <!USELESS_IS_CHECK!>is Any?<!> -> a.<!UNRESOLVED_REFERENCE!>bar<!>()
-    is C -> a.bar()
-    else -> a?.foo()
+    <!USELESS_IS_CHECK!>is C<!> -> a.bar()
+    else -> a<!UNNECESSARY_SAFE_CALL!>?.<!>foo()
   }
 
   if (<!USELESS_IS_CHECK!>a is Any?<!>) {

compiler/testData/ir/irText/expressions/bangbang.fir.ir.txt

@@ -56,5 +56,5 @@ FILE fqName:<root> fileName:/bangbang.kt
           then: CALL 'public final fun useString (s: kotlin.String): kotlin.Unit declared in <root>' type=kotlin.Unit origin=null
             s: CALL 'public final fun CHECK_NOT_NULL <T0> (arg0: T0 of kotlin.internal.ir.CHECK_NOT_NULL?): {T0 of kotlin.internal.ir.CHECK_NOT_NULL & Any} declared in kotlin.internal.ir' type=kotlin.String origin=EXCLEXCL
               <T0>: kotlin.String
-              arg0: TYPE_OP type=kotlin.String? origin=IMPLICIT_CAST typeOperand=kotlin.String?
+              arg0: TYPE_OP type=kotlin.String origin=IMPLICIT_CAST typeOperand=kotlin.String
                 GET_VAR 'a: X of <root>.test4 declared in <root>.test4' type=X of <root>.test4 origin=null

compiler/testData/ir/irText/expressions/bangbang.fir.kt.txt

@@ -24,6 +24,6 @@ fun <X : Any?> test4(a: X) {
     a is String? -> CHECK_NOT_NULL<String>(arg0 = a /*as String? */) /*~> Unit */
   }
   when {
-    a is String? -> useString(s = CHECK_NOT_NULL<String>(arg0 = a /*as String? */))
+    a is String? -> useString(s = CHECK_NOT_NULL<String>(arg0 = a /*as String */))
   }
 }