FIR DFA: do not remove statements about LHS of !!

Value equality statements about the result also propagate to left-hand
side, so these statements can still be useful.

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/dfa/FirDataFlowAnalyzer.kt

@@ -678,30 +678,14 @@ abstract class FirDataFlowAnalyzer<FLOW : Flow>(
         val (node, unionNode) = graphBuilder.exitCheckNotNullCall(checkNotNullCall, callCompleted)
         node.mergeIncomingFlow()
 
-        checkNotNullCall.argument.propagateNotNullInfo(node)
+        val argumentVariable = variableStorage.getOrCreateVariable(node.previousFlow, checkNotNullCall.argument)
+        node.flow.assumeNotNull(argumentVariable, shouldForkFlow = false, shouldRemoveSynthetics = false)
 
         unionNode?.let { unionFlowFromArguments(it) }
     }
 
-    private fun FirExpression.propagateNotNullInfo(node: CFGNode<*>) {
-        val symbol = this.symbol
-        if (symbol != null) {
-            variableStorage.getOrCreateRealVariable(node.previousFlow, symbol, this)?.let { operandVariable ->
-                node.flow.assumeNotNull(operandVariable, shouldForkFlow = false, shouldRemoveSynthetics = true)
-            }
-        }
-        when (this) {
-            is FirSafeCallExpression -> receiver.propagateNotNullInfo(node)
-            is FirTypeOperatorCall -> {
-                if (operation == FirOperation.AS || operation == FirOperation.SAFE_AS) {
-                    argument.propagateNotNullInfo(node)
-                }
-            }
-        }
-    }
-
     private fun FLOW.assumeNotNull(variable: DataFlowVariable, shouldForkFlow: Boolean, shouldRemoveSynthetics: Boolean): FLOW =
-        logicSystem.approveStatementsInsideFlow(this, variable notEq null, shouldForkFlow, shouldRemoveSynthetics,).also {
+        logicSystem.approveStatementsInsideFlow(this, variable notEq null, shouldForkFlow, shouldRemoveSynthetics).also {
             if (variable is RealVariable) {
                 it.addTypeStatement(variable typeEq any andTypeNotEq nullableNothing)
             }
@@ -1380,7 +1364,8 @@ abstract class FirDataFlowAnalyzer<FLOW : Flow>(
         node.mergeIncomingFlow()
         mergePostponedLambdaExitsNode?.mergeIncomingFlow()
         if (isLhsNotNull) {
-            elvisExpression.lhs.propagateNotNullInfo(node)
+            val lhsVariable = variableStorage.getOrCreateVariable(node.previousFlow, elvisExpression.lhs)
+            node.flow.assumeNotNull(lhsVariable, shouldForkFlow = false, shouldRemoveSynthetics = true)
         }
 
         if (!components.session.languageVersionSettings.supportsFeature(LanguageFeature.BooleanElvisBoundSmartCasts)) return
@@ -1396,7 +1381,7 @@ abstract class FirDataFlowAnalyzer<FLOW : Flow>(
             val lhsVariable = variableStorage.getOrCreateVariable(flow, lhs)
 
             val value = rhs.value as Boolean
-            flow.addImplication(elvisVariable.eq(!value) implies (lhsVariable.notEq(null)))
+            flow.addImplication((elvisVariable eq !value) implies (lhsVariable notEq null))
         }
     }
 

compiler/tests-spec/testData/diagnostics/notLinked/contracts/analysis/smartcasts/pos/14.fir.kt

@@ -63,7 +63,7 @@ fun case_2(value_1: Int?) {
 // TESTCASE NUMBER: 3
 fun case_3(value_1: Int?) {
     if (contracts.case_3(value_1)!!) {
-        value_1<!UNSAFE_CALL!>.<!>inv()
+        value_1.inv()
     }
 }
 

compiler/tests-spec/testData/diagnostics/notLinked/dfa/pos/25.fir.kt

@@ -49,7 +49,7 @@ inline fun <reified T : CharSequence>case_3(x: Any?) {
 // TESTCASE NUMBER: 4
 inline fun <reified T : CharSequence>case_4(x: Any?) {
     (x as? T)!!
-    if (x is T?) {
+    if (<!USELESS_IS_CHECK!>x is T?<!>) {
         <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Any? & T?!!")!>x<!>
         <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Any? & T?!!")!>x<!>.length
         <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Any? & T?!!")!>x<!>.get(0)

compiler/tests-spec/testData/diagnostics/notLinked/dfa/pos/26.fir.kt

@@ -49,7 +49,7 @@ inline fun <reified T : CharSequence>case_3(x: Any?) {
 // TESTCASE NUMBER: 4
 inline fun <reified T : CharSequence>case_4(x: Any?) {
     (x as? T)!!
-    if (x is T?) {
+    if (<!USELESS_IS_CHECK!>x is T?<!>) {
         <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Any? & T?!!")!>x<!>
         <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Any? & T?!!")!>x<!>.length
         <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Any? & T?!!")!>x<!>.get(0)

compiler/tests-spec/testData/diagnostics/notLinked/dfa/pos/27.fir.kt

@@ -49,7 +49,7 @@ inline fun <reified T : CharSequence>case_3(x: Any?) {
 // TESTCASE NUMBER: 4
 inline fun <reified T : CharSequence>case_4(x: Any?) {
     (x as? T)!!
-    if (x is T?) {
+    if (<!USELESS_IS_CHECK!>x is T?<!>) {
         <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Any? & T?!!")!>x<!>
         <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Any? & T?!!")!>x<!>.length
         <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Any? & T?!!")!>x<!>.get(0)