[FIR] Fix issue with multiple smartcasts of this.

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

@@ -32,6 +32,8 @@ import org.jetbrains.kotlin.fir.symbols.CallableId
 import org.jetbrains.kotlin.fir.symbols.impl.FirNamedFunctionSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirVariableSymbol
 import org.jetbrains.kotlin.fir.types.*
+import org.jetbrains.kotlin.fir.unwrapSmartcast
+import org.jetbrains.kotlin.fir.unwrapWhenSubjectExpression
 import org.jetbrains.kotlin.fir.visitors.transformSingle
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
@@ -838,23 +840,15 @@ class FirDataFlowAnalyzer(private val components: FirAbstractBodyResolveTransfor
     private fun getOrCreateSyntheticVariable(fir: FirElement): SyntheticDataFlowVariable =
         variableStorage.getOrCreateNewSyntheticVariable(fir)
 
-    private fun FirElement.unwrapWhenSubjectExpression(): FirElement = if (this is FirWhenSubjectExpression) {
-        val whenExpression = whenSubject.whenExpression
-        whenExpression.subjectVariable
-            ?: whenExpression.subject
-            ?: throw IllegalStateException("Subject or subject variable must be not null")
-    } else {
-        this
-    }
-
     private fun getOrCreateRealVariable(fir: FirElement): RealDataFlowVariable? {
         @Suppress("NAME_SHADOWING")
-        val fir = fir.unwrapWhenSubjectExpression()
+        val fir = fir.unwrapWhenSubjectExpression().unwrapSmartcast()
-        if (fir is FirThisReceiverExpressionImpl) {
+        val symbol = fir.resolvedSymbol ?: return null
-            return variableStorage.getOrCreateNewThisRealVariable(fir.calleeReference.boundSymbol ?: return null)
+        return when {
+            fir is FirThisReceiverExpressionImpl -> variableStorage.getOrCreateNewThisRealVariable(symbol)
+            symbol is FirVariableSymbol<*> -> variableStorage.getOrCreateNewRealVariable(symbol).variableUnderAlias
+            else -> null
         }
-        val symbol = fir.resolvedSymbol as? FirVariableSymbol<*> ?: return null
-        return variableStorage.getOrCreateNewRealVariable(symbol).variableUnderAlias
     }
 
     private fun getOrCreateVariable(fir: FirElement): DataFlowVariable {

compiler/fir/resolve/testData/resolve/smartcasts/implicitReceivers.dot

@@ -21,77 +21,89 @@ digraph implicitReceivers_kt {
 
   subgraph cluster_2 {
     color=red
-    4 [label="Enter function with" style="filled" fillcolor=red];
+    4 [label="Enter function <init>" style="filled" fillcolor=red];
-    5 [label="Exit function with" style="filled" fillcolor=red];
+    5 [label="Exit function <init>" style="filled" fillcolor=red];
   }
 
   4 -> {5};
 
   subgraph cluster_3 {
     color=red
-    6 [label="Enter function test_1" style="filled" fillcolor=red];
+    6 [label="Enter function bar" style="filled" fillcolor=red];
-    subgraph cluster_4 {
+    7 [label="Exit function bar" style="filled" fillcolor=red];
-      color=blue
-      7 [label="Enter when"];
-      subgraph cluster_5 {
-        color=blue
-        8 [label="Enter when branch condition "];
-        9 [label="Access variable this@R|/test_1|"];
-        10 [label="Type operator: this is A"];
-        11 [label="Exit when branch condition"];
-      }
-      subgraph cluster_6 {
-        color=blue
-        12 [label="Enter when branch condition else"];
-        13 [label="Exit when branch condition"];
-      }
-      14 [label="Enter when branch result"];
-      subgraph cluster_7 {
-        color=blue
-        15 [label="Enter block"];
-        16 [label="Access variable this@R|/test_1|"];
-        17 [label="Function call: this@R|/test_1|.<Unresolved name: foo>#()"];
-        18 [label="Function call: <Unresolved name: foo>#()"];
-        19 [label="Exit block"];
-      }
-      20 [label="Exit when branch result"];
-      21 [label="Enter when branch result"];
-      subgraph cluster_8 {
-        color=blue
-        22 [label="Enter block"];
-        23 [label="Access variable this@R|/test_1|"];
-        24 [label="Function call: this@R|/test_1|.R|/A.foo|()"];
-        25 [label="Function call: this@R|/A|.R|/A.foo|()"];
-        26 [label="Exit block"];
-      }
-      27 [label="Exit when branch result"];
-      28 [label="Exit when"];
-    }
-    29 [label="Access variable this@R|/test_1|"];
-    30 [label="Function call: this@R|/test_1|.<Unresolved name: foo>#()"];
-    31 [label="Function call: <Unresolved name: foo>#()"];
-    32 [label="Exit function test_1" style="filled" fillcolor=red];
   }
 
   6 -> {7};
-  7 -> {8};
+
+  subgraph cluster_4 {
+    color=red
+    8 [label="Enter function with" style="filled" fillcolor=red];
+    9 [label="Exit function with" style="filled" fillcolor=red];
+  }
+
   8 -> {9};
-  9 -> {10};
+
+  subgraph cluster_5 {
+    color=red
+    10 [label="Enter function test_1" style="filled" fillcolor=red];
+    subgraph cluster_6 {
+      color=blue
+      11 [label="Enter when"];
+      subgraph cluster_7 {
+        color=blue
+        12 [label="Enter when branch condition "];
+        13 [label="Access variable this@R|/test_1|"];
+        14 [label="Type operator: this is A"];
+        15 [label="Exit when branch condition"];
+      }
+      subgraph cluster_8 {
+        color=blue
+        16 [label="Enter when branch condition else"];
+        17 [label="Exit when branch condition"];
+      }
+      18 [label="Enter when branch result"];
+      subgraph cluster_9 {
+        color=blue
+        19 [label="Enter block"];
+        20 [label="Access variable this@R|/test_1|"];
+        21 [label="Function call: this@R|/test_1|.<Unresolved name: foo>#()"];
+        22 [label="Function call: <Unresolved name: foo>#()"];
+        23 [label="Exit block"];
+      }
+      24 [label="Exit when branch result"];
+      25 [label="Enter when branch result"];
+      subgraph cluster_10 {
+        color=blue
+        26 [label="Enter block"];
+        27 [label="Access variable this@R|/test_1|"];
+        28 [label="Function call: this@R|/test_1|.R|/A.foo|()"];
+        29 [label="Function call: this@R|/A|.R|/A.foo|()"];
+        30 [label="Exit block"];
+      }
+      31 [label="Exit when branch result"];
+      32 [label="Exit when"];
+    }
+    33 [label="Access variable this@R|/test_1|"];
+    34 [label="Function call: this@R|/test_1|.<Unresolved name: foo>#()"];
+    35 [label="Function call: <Unresolved name: foo>#()"];
+    36 [label="Exit function test_1" style="filled" fillcolor=red];
+  }
+
   10 -> {11};
-  11 -> {21 12};
+  11 -> {12};
   12 -> {13};
   13 -> {14};
   14 -> {15};
-  15 -> {16};
+  15 -> {25 16};
   16 -> {17};
   17 -> {18};
   18 -> {19};
   19 -> {20};
-  20 -> {28};
+  20 -> {21};
   21 -> {22};
   22 -> {23};
   23 -> {24};
-  24 -> {25};
+  24 -> {32};
   25 -> {26};
   26 -> {27};
   27 -> {28};
@@ -99,72 +111,72 @@ digraph implicitReceivers_kt {
   29 -> {30};
   30 -> {31};
   31 -> {32};
-
+  32 -> {33};
-  subgraph cluster_9 {
-    color=red
-    33 [label="Enter function test_2" style="filled" fillcolor=red];
-    subgraph cluster_10 {
-      color=blue
-      34 [label="Enter when"];
-      subgraph cluster_11 {
-        color=blue
-        35 [label="Enter when branch condition "];
-        36 [label="Access variable this@R|/test_2|"];
-        37 [label="Type operator: this !is A"];
-        38 [label="Exit when branch condition"];
-      }
-      subgraph cluster_12 {
-        color=blue
-        39 [label="Enter when branch condition else"];
-        40 [label="Exit when branch condition"];
-      }
-      41 [label="Enter when branch result"];
-      subgraph cluster_13 {
-        color=blue
-        42 [label="Enter block"];
-        43 [label="Access variable this@R|/test_2|"];
-        44 [label="Function call: this@R|/test_2|.R|/A.foo|()"];
-        45 [label="Function call: this@R|/A|.R|/A.foo|()"];
-        46 [label="Exit block"];
-      }
-      47 [label="Exit when branch result"];
-      48 [label="Enter when branch result"];
-      subgraph cluster_14 {
-        color=blue
-        49 [label="Enter block"];
-        50 [label="Access variable this@R|/test_2|"];
-        51 [label="Function call: this@R|/test_2|.<Unresolved name: foo>#()"];
-        52 [label="Function call: <Unresolved name: foo>#()"];
-        53 [label="Exit block"];
-      }
-      54 [label="Exit when branch result"];
-      55 [label="Exit when"];
-    }
-    56 [label="Access variable this@R|/test_2|"];
-    57 [label="Function call: this@R|/test_2|.<Unresolved name: foo>#()"];
-    58 [label="Function call: <Unresolved name: foo>#()"];
-    59 [label="Exit function test_2" style="filled" fillcolor=red];
-  }
-
   33 -> {34};
   34 -> {35};
   35 -> {36};
-  36 -> {37};
+
+  subgraph cluster_11 {
+    color=red
+    37 [label="Enter function test_2" style="filled" fillcolor=red];
+    subgraph cluster_12 {
+      color=blue
+      38 [label="Enter when"];
+      subgraph cluster_13 {
+        color=blue
+        39 [label="Enter when branch condition "];
+        40 [label="Access variable this@R|/test_2|"];
+        41 [label="Type operator: this !is A"];
+        42 [label="Exit when branch condition"];
+      }
+      subgraph cluster_14 {
+        color=blue
+        43 [label="Enter when branch condition else"];
+        44 [label="Exit when branch condition"];
+      }
+      45 [label="Enter when branch result"];
+      subgraph cluster_15 {
+        color=blue
+        46 [label="Enter block"];
+        47 [label="Access variable this@R|/test_2|"];
+        48 [label="Function call: this@R|/test_2|.R|/A.foo|()"];
+        49 [label="Function call: this@R|/A|.R|/A.foo|()"];
+        50 [label="Exit block"];
+      }
+      51 [label="Exit when branch result"];
+      52 [label="Enter when branch result"];
+      subgraph cluster_16 {
+        color=blue
+        53 [label="Enter block"];
+        54 [label="Access variable this@R|/test_2|"];
+        55 [label="Function call: this@R|/test_2|.<Unresolved name: foo>#()"];
+        56 [label="Function call: <Unresolved name: foo>#()"];
+        57 [label="Exit block"];
+      }
+      58 [label="Exit when branch result"];
+      59 [label="Exit when"];
+    }
+    60 [label="Access variable this@R|/test_2|"];
+    61 [label="Function call: this@R|/test_2|.<Unresolved name: foo>#()"];
+    62 [label="Function call: <Unresolved name: foo>#()"];
+    63 [label="Exit function test_2" style="filled" fillcolor=red];
+  }
+
   37 -> {38};
-  38 -> {48 39};
+  38 -> {39};
   39 -> {40};
   40 -> {41};
   41 -> {42};
-  42 -> {43};
+  42 -> {52 43};
   43 -> {44};
   44 -> {45};
   45 -> {46};
   46 -> {47};
-  47 -> {55};
+  47 -> {48};
   48 -> {49};
   49 -> {50};
   50 -> {51};
-  51 -> {52};
+  51 -> {59};
   52 -> {53};
   53 -> {54};
   54 -> {55};
@@ -172,41 +184,45 @@ digraph implicitReceivers_kt {
   56 -> {57};
   57 -> {58};
   58 -> {59};
+  59 -> {60};
+  60 -> {61};
+  61 -> {62};
+  62 -> {63};
 
-  subgraph cluster_15 {
+  subgraph cluster_17 {
     color=red
-    60 [label="Enter function test_3" style="filled" fillcolor=red];
+    64 [label="Enter function test_3" style="filled" fillcolor=red];
-    61 [label="Access variable R|<local>/a|"];
+    65 [label="Access variable R|<local>/a|"];
-    subgraph cluster_16 {
+    subgraph cluster_18 {
       color=blue
-      62 [label="Enter function anonymousFunction"];
+      66 [label="Enter function anonymousFunction"];
-      63 [label="Access variable R|<local>/b|"];
+      67 [label="Access variable R|<local>/b|"];
-      subgraph cluster_17 {
+      subgraph cluster_19 {
         color=blue
-        64 [label="Enter function anonymousFunction"];
+        68 [label="Enter function anonymousFunction"];
-        65 [label="Access variable R|<local>/c|"];
+        69 [label="Access variable R|<local>/c|"];
-        subgraph cluster_18 {
+        subgraph cluster_20 {
           color=blue
-          66 [label="Enter function anonymousFunction"];
+          70 [label="Enter function anonymousFunction"];
-          67 [label="Access variable this@R|special/anonymous|"];
+          71 [label="Access variable this@R|special/anonymous|"];
-          68 [label="Type operator: this@wb as A"];
+          72 [label="Type operator: this@wb as A"];
-          69 [label="Access variable this@R|special/anonymous|"];
+          73 [label="Access variable this@R|special/anonymous|"];
-          70 [label="Function call: this@R|special/anonymous|.R|/A.foo|()"];
+          74 [label="Function call: this@R|special/anonymous|.R|/A.foo|()"];
-          71 [label="Function call: this@R|/A|.R|/A.foo|()"];
+          75 [label="Function call: this@R|/A|.R|/A.foo|()"];
-          72 [label="Exit function anonymousFunction"];
+          76 [label="Exit function anonymousFunction"];
         }
-        73 [label="Function call: R|kotlin/with|<R|kotlin/Any|, R|kotlin/Unit|>(R|<local>/c|, <L> = wc@fun R|kotlin/Any|.<anonymous>(): R|kotlin/Unit| <kind=EXACTLY_ONCE>  {
+        77 [label="Function call: R|kotlin/with|<R|kotlin/Any|, R|kotlin/Unit|>(R|<local>/c|, <L> = wc@fun R|kotlin/Any|.<anonymous>(): R|kotlin/Unit| <kind=EXACTLY_ONCE>  {
     (this@R|special/anonymous| as R|A|)
     this@R|special/anonymous|.R|/A.foo|()
     this@R|/A|.R|/A.foo|()
 }
 )"];
-        74 [label="Access variable this@R|special/anonymous|"];
+        78 [label="Access variable this@R|special/anonymous|"];
-        75 [label="Function call: this@R|special/anonymous|.R|/A.foo|()"];
+        79 [label="Function call: this@R|special/anonymous|.R|/A.foo|()"];
-        76 [label="Function call: this@R|/A|.R|/A.foo|()"];
+        80 [label="Function call: this@R|/A|.R|/A.foo|()"];
-        77 [label="Exit function anonymousFunction"];
+        81 [label="Exit function anonymousFunction"];
       }
-      78 [label="Function call: R|kotlin/with|<R|kotlin/Any|, R|kotlin/Unit|>(R|<local>/b|, <L> = wb@fun R|kotlin/Any|.<anonymous>(): R|kotlin/Unit| <kind=EXACTLY_ONCE>  {
+      82 [label="Function call: R|kotlin/with|<R|kotlin/Any|, R|kotlin/Unit|>(R|<local>/b|, <L> = wb@fun R|kotlin/Any|.<anonymous>(): R|kotlin/Unit| <kind=EXACTLY_ONCE>  {
     R|kotlin/with|<R|kotlin/Any|, R|kotlin/Unit|>(R|<local>/c|, <L> = wc@fun R|kotlin/Any|.<anonymous>(): R|kotlin/Unit| <kind=EXACTLY_ONCE>  {
         (this@R|special/anonymous| as R|A|)
         this@R|special/anonymous|.R|/A.foo|()
@@ -217,9 +233,9 @@ digraph implicitReceivers_kt {
     this@R|/A|.R|/A.foo|()
 }
 )"];
-      79 [label="Exit function anonymousFunction"];
+      83 [label="Exit function anonymousFunction"];
     }
-    80 [label="Function call: R|kotlin/with|<R|kotlin/Any|, R|kotlin/Unit|>(R|<local>/a|, <L> = wa@fun R|kotlin/Any|.<anonymous>(): R|kotlin/Unit| <kind=EXACTLY_ONCE>  {
+    84 [label="Function call: R|kotlin/with|<R|kotlin/Any|, R|kotlin/Unit|>(R|<local>/a|, <L> = wa@fun R|kotlin/Any|.<anonymous>(): R|kotlin/Unit| <kind=EXACTLY_ONCE>  {
     R|kotlin/with|<R|kotlin/Any|, R|kotlin/Unit|>(R|<local>/b|, <L> = wb@fun R|kotlin/Any|.<anonymous>(): R|kotlin/Unit| <kind=EXACTLY_ONCE>  {
         R|kotlin/with|<R|kotlin/Any|, R|kotlin/Unit|>(R|<local>/c|, <L> = wc@fun R|kotlin/Any|.<anonymous>(): R|kotlin/Unit| <kind=EXACTLY_ONCE>  {
             (this@R|special/anonymous| as R|A|)
@@ -233,13 +249,9 @@ digraph implicitReceivers_kt {
     )
 }
 )"];
-    81 [label="Exit function test_3" style="filled" fillcolor=red];
+    85 [label="Exit function test_3" style="filled" fillcolor=red];
   }
 
-  60 -> {61};
-  61 -> {62};
-  62 -> {63};
-  63 -> {64};
   64 -> {65};
   65 -> {66};
   66 -> {67};
@@ -257,5 +269,278 @@ digraph implicitReceivers_kt {
   78 -> {79};
   79 -> {80};
   80 -> {81};
+  81 -> {82};
+  82 -> {83};
+  83 -> {84};
+  84 -> {85};
+
+  subgraph cluster_21 {
+    color=red
+    86 [label="Enter function test_4" style="filled" fillcolor=red];
+    subgraph cluster_22 {
+      color=blue
+      87 [label="Enter when"];
+      subgraph cluster_23 {
+        color=blue
+        88 [label="Enter when branch condition "];
+        89 [label="Access variable this@R|/test_4|"];
+        90 [label="Type operator: this !is A"];
+        91 [label="Exit when branch condition"];
+      }
+      subgraph cluster_24 {
+        color=blue
+        92 [label="Enter when branch condition else"];
+        93 [label="Exit when branch condition"];
+      }
+      94 [label="Enter when branch result"];
+      subgraph cluster_25 {
+        color=blue
+        95 [label="Enter block"];
+        subgraph cluster_26 {
+          color=blue
+          96 [label="Enter when"];
+          subgraph cluster_27 {
+            color=blue
+            97 [label="Enter when branch condition "];
+            98 [label="Access variable this@R|/test_4|"];
+            99 [label="Type operator: this !is B"];
+            100 [label="Exit when branch condition"];
+          }
+          subgraph cluster_28 {
+            color=blue
+            101 [label="Enter when branch condition else"];
+            102 [label="Exit when branch condition"];
+          }
+          103 [label="Enter when branch result"];
+          subgraph cluster_29 {
+            color=blue
+            104 [label="Enter block"];
+            105 [label="Access variable this@R|/test_4|"];
+            106 [label="Function call: this@R|/test_4|.R|/A.foo|()"];
+            107 [label="Function call: this@R|/A|.R|/A.foo|()"];
+            108 [label="Access variable this@R|/test_4|"];
+            109 [label="Function call: this@R|/test_4|.R|/B.bar|()"];
+            110 [label="Function call: this@R|/B|.R|/B.bar|()"];
+            111 [label="Exit block"];
+          }
+          112 [label="Exit when branch result"];
+          113 [label="Enter when branch result"];
+          subgraph cluster_30 {
+            color=blue
+            114 [label="Enter block"];
+            115 [label="Access variable this@R|/test_4|"];
+            116 [label="Function call: this@R|/test_4|.<Unresolved name: bar>#()"];
+            117 [label="Function call: <Unresolved name: bar>#()"];
+            118 [label="Access variable this@R|/test_4|"];
+            119 [label="Function call: this@R|/test_4|.R|/A.foo|()"];
+            120 [label="Function call: this@R|/A|.R|/A.foo|()"];
+            121 [label="Exit block"];
+          }
+          122 [label="Exit when branch result"];
+          123 [label="Exit when"];
+        }
+        124 [label="Exit block"];
+      }
+      125 [label="Exit when branch result"];
+      126 [label="Enter when branch result"];
+      subgraph cluster_31 {
+        color=blue
+        127 [label="Enter block"];
+        128 [label="Access variable this@R|/test_4|"];
+        129 [label="Function call: this@R|/test_4|.<Unresolved name: foo>#()"];
+        130 [label="Function call: <Unresolved name: foo>#()"];
+        131 [label="Access variable this@R|/test_4|"];
+        132 [label="Function call: this@R|/test_4|.<Unresolved name: bar>#()"];
+        133 [label="Function call: <Unresolved name: bar>#()"];
+        134 [label="Exit block"];
+      }
+      135 [label="Exit when branch result"];
+      136 [label="Exit when"];
+    }
+    137 [label="Access variable this@R|/test_4|"];
+    138 [label="Function call: this@R|/test_4|.<Unresolved name: foo>#()"];
+    139 [label="Function call: <Unresolved name: foo>#()"];
+    140 [label="Access variable this@R|/test_4|"];
+    141 [label="Function call: this@R|/test_4|.<Unresolved name: bar>#()"];
+    142 [label="Function call: <Unresolved name: bar>#()"];
+    143 [label="Exit function test_4" style="filled" fillcolor=red];
+  }
+
+  86 -> {87};
+  87 -> {88};
+  88 -> {89};
+  89 -> {90};
+  90 -> {91};
+  91 -> {126 92};
+  92 -> {93};
+  93 -> {94};
+  94 -> {95};
+  95 -> {96};
+  96 -> {97};
+  97 -> {98};
+  98 -> {99};
+  99 -> {100};
+  100 -> {113 101};
+  101 -> {102};
+  102 -> {103};
+  103 -> {104};
+  104 -> {105};
+  105 -> {106};
+  106 -> {107};
+  107 -> {108};
+  108 -> {109};
+  109 -> {110};
+  110 -> {111};
+  111 -> {112};
+  112 -> {123};
+  113 -> {114};
+  114 -> {115};
+  115 -> {116};
+  116 -> {117};
+  117 -> {118};
+  118 -> {119};
+  119 -> {120};
+  120 -> {121};
+  121 -> {122};
+  122 -> {123};
+  123 -> {124};
+  124 -> {125};
+  125 -> {136};
+  126 -> {127};
+  127 -> {128};
+  128 -> {129};
+  129 -> {130};
+  130 -> {131};
+  131 -> {132};
+  132 -> {133};
+  133 -> {134};
+  134 -> {135};
+  135 -> {136};
+  136 -> {137};
+  137 -> {138};
+  138 -> {139};
+  139 -> {140};
+  140 -> {141};
+  141 -> {142};
+  142 -> {143};
+
+  subgraph cluster_32 {
+    color=red
+    144 [label="Enter function test_5" style="filled" fillcolor=red];
+    subgraph cluster_33 {
+      color=blue
+      145 [label="Enter when"];
+      subgraph cluster_34 {
+        color=blue
+        146 [label="Enter when branch condition "];
+        147 [label="Access variable this@R|/test_5|"];
+        148 [label="Type operator: this is List<*>"];
+        149 [label="Exit when branch condition"];
+      }
+      subgraph cluster_35 {
+        color=blue
+        150 [label="Enter when branch condition "];
+        151 [label="Access variable this@R|/test_5|"];
+        152 [label="Type operator: this is String"];
+        153 [label="Exit when branch condition"];
+      }
+      subgraph cluster_36 {
+        color=blue
+        154 [label="Enter when branch condition else"];
+        155 [label="Exit when branch condition"];
+      }
+      156 [label="Enter when branch result"];
+      subgraph cluster_37 {
+        color=blue
+        157 [label="Enter block"];
+        158 [label="Const: Int(0)"];
+        159 [label="Exit block"];
+      }
+      160 [label="Exit when branch result"];
+      161 [label="Enter when branch result"];
+      subgraph cluster_38 {
+        color=blue
+        162 [label="Enter block"];
+        163 [label="Access variable R|kotlin/String.length|"];
+        164 [label="Exit block"];
+      }
+      165 [label="Exit when branch result"];
+      166 [label="Enter when branch result"];
+      subgraph cluster_39 {
+        color=blue
+        167 [label="Enter block"];
+        168 [label="Access variable R|kotlin/collections/List.size|"];
+        169 [label="Exit block"];
+      }
+      170 [label="Exit when branch result"];
+      171 [label="Exit when"];
+    }
+    172 [label="Jump: ^test_5 when () {
+    (this@R|/test_5| is R|kotlin/collections/List<*>|) ->  {
+        this@R|kotlin/collections/List|.R|kotlin/collections/List.size|
+    }
+    (this@R|/test_5| is R|kotlin/String|) ->  {
+        this@R|kotlin/String|.R|kotlin/String.length|
+    }
+    else ->  {
+        Int(0)
+    }
+}
+"];
+    173 [label="Stub" style="filled" fillcolor=gray];
+    174 [label="Exit function test_5" style="filled" fillcolor=red];
+  }
+
+  144 -> {145};
+  145 -> {146};
+  146 -> {147};
+  147 -> {148};
+  148 -> {149};
+  149 -> {166 150};
+  150 -> {151};
+  151 -> {152};
+  152 -> {153};
+  153 -> {161 154};
+  154 -> {155};
+  155 -> {156};
+  156 -> {157};
+  157 -> {158};
+  158 -> {159};
+  159 -> {160};
+  160 -> {171};
+  161 -> {162};
+  162 -> {163};
+  163 -> {164};
+  164 -> {165};
+  165 -> {171};
+  166 -> {167};
+  167 -> {168};
+  168 -> {169};
+  169 -> {170};
+  170 -> {171};
+  171 -> {172};
+  172 -> {174};
+  172 -> {173} [style=dotted];
+  173 -> {174} [style=dotted];
+
+  subgraph cluster_40 {
+    color=red
+    175 [label="Enter function test_6" style="filled" fillcolor=red];
+    176 [label="Access variable this@R|/test_6|"];
+    177 [label="Type operator: this as List<*>"];
+    178 [label="Access variable R|kotlin/collections/List.size|"];
+    179 [label="Access variable this@R|/test_6|"];
+    180 [label="Type operator: this as String"];
+    181 [label="Access variable R|kotlin/String.length|"];
+    182 [label="Exit function test_6" style="filled" fillcolor=red];
+  }
+
+  175 -> {176};
+  176 -> {177};
+  177 -> {178};
+  178 -> {179};
+  179 -> {180};
+  180 -> {181};
+  181 -> {182};
 
 }

compiler/fir/resolve/testData/resolve/smartcasts/implicitReceivers.kt

@@ -2,6 +2,10 @@ class A {
     fun foo() {}
 }
 
+class B {
+    fun bar() {}
+}
+
 fun <T> T.with(block: T.() -> Unit) {}
 
 fun Any?.test_1() {
@@ -28,7 +32,6 @@ fun Any?.test_2() {
     <!UNRESOLVED_REFERENCE!>foo<!>()
 }
 
-
 fun test_3(a: Any, b: Any, c: Any) {
     with(a) wa@{
         with(b) wb@{
@@ -41,4 +44,40 @@ fun test_3(a: Any, b: Any, c: Any) {
             foo()
         }
     }
+}
+
+fun Any?.test_4() {
+    if (this !is A) {
+        this.<!UNRESOLVED_REFERENCE!>foo<!>()
+        <!UNRESOLVED_REFERENCE!>foo<!>()
+        this.<!UNRESOLVED_REFERENCE!>bar<!>()
+        <!UNRESOLVED_REFERENCE!>bar<!>()
+    } else if (this !is B) {
+        this.<!UNRESOLVED_REFERENCE!>bar<!>()
+        <!UNRESOLVED_REFERENCE!>bar<!>()
+        this.foo()
+        foo()
+    } else {
+        this.foo()
+        foo()
+        this.bar()
+        bar()
+    }
+    this.<!UNRESOLVED_REFERENCE!>foo<!>()
+    <!UNRESOLVED_REFERENCE!>foo<!>()
+    this.<!UNRESOLVED_REFERENCE!>bar<!>()
+    <!UNRESOLVED_REFERENCE!>bar<!>()
+}
+
+fun Any.test_5(): Int = when {
+    this is List<*> -> size
+    this is String -> length
+    else -> 0
+}
+
+fun Any.test_6() {
+    this as List<*>
+    size
+    this as String
+    length
 }

compiler/fir/resolve/testData/resolve/smartcasts/implicitReceivers.txt

@@ -7,6 +7,15 @@ FILE: implicitReceivers.kt
         public final fun foo(): R|kotlin/Unit| {
         }
 
+    }
+    public final class B : R|kotlin/Any| {
+        public constructor(): R|B| {
+            super<R|kotlin/Any|>()
+        }
+
+        public final fun bar(): R|kotlin/Unit| {
+        }
+
     }
     public final fun <T> R|T|.with(block: R|T.() -> kotlin/Unit|): R|kotlin/Unit| {
     }
@@ -56,3 +65,55 @@ FILE: implicitReceivers.kt
         }
         )
     }
+    public final fun R|kotlin/Any?|.test_4(): R|kotlin/Unit| {
+        when () {
+            (this@R|/test_4| !is R|A|) ->  {
+                this@R|/test_4|.<Unresolved name: foo>#()
+                <Unresolved name: foo>#()
+                this@R|/test_4|.<Unresolved name: bar>#()
+                <Unresolved name: bar>#()
+            }
+            else ->  {
+                when () {
+                    (this@R|/test_4| !is R|B|) ->  {
+                        this@R|/test_4|.<Unresolved name: bar>#()
+                        <Unresolved name: bar>#()
+                        this@R|/test_4|.R|/A.foo|()
+                        this@R|/A|.R|/A.foo|()
+                    }
+                    else ->  {
+                        this@R|/test_4|.R|/A.foo|()
+                        this@R|/A|.R|/A.foo|()
+                        this@R|/test_4|.R|/B.bar|()
+                        this@R|/B|.R|/B.bar|()
+                    }
+                }
+
+            }
+        }
+
+        this@R|/test_4|.<Unresolved name: foo>#()
+        <Unresolved name: foo>#()
+        this@R|/test_4|.<Unresolved name: bar>#()
+        <Unresolved name: bar>#()
+    }
+    public final fun R|kotlin/Any|.test_5(): R|kotlin/Int| {
+        ^test_5 when () {
+            (this@R|/test_5| is R|kotlin/collections/List<*>|) ->  {
+                this@R|kotlin/collections/List|.R|kotlin/collections/List.size|
+            }
+            (this@R|/test_5| is R|kotlin/String|) ->  {
+                this@R|kotlin/String|.R|kotlin/String.length|
+            }
+            else ->  {
+                Int(0)
+            }
+        }
+
+    }
+    public final fun R|kotlin/Any|.test_6(): R|kotlin/Unit| {
+        (this@R|/test_6| as R|kotlin/collections/List<*>|)
+        this@R|kotlin/collections/List|.R|kotlin/collections/List.size|
+        (this@R|/test_6| as R|kotlin/String|)
+        this@R|kotlin/String|.R|kotlin/String.length|
+    }

compiler/fir/tree/src/org/jetbrains/kotlin/fir/Utils.kt

@@ -8,9 +8,26 @@ package org.jetbrains.kotlin.fir
 import org.jetbrains.kotlin.analyzer.ModuleInfo
 import org.jetbrains.kotlin.fir.expressions.FirBlock
 import org.jetbrains.kotlin.fir.expressions.FirExpression
+import org.jetbrains.kotlin.fir.expressions.FirExpressionWithSmartcast
+import org.jetbrains.kotlin.fir.expressions.FirWhenSubjectExpression
 import org.jetbrains.kotlin.fir.visitors.FirTransformer
 
 fun ModuleInfo.dependenciesWithoutSelf(): Sequence<ModuleInfo> = dependencies().asSequence().filter { it != this }
 
 // TODO: rewrite
-fun FirBlock.returnExpressions(): List<FirExpression> = listOfNotNull(statements.lastOrNull() as? FirExpression)
+fun FirBlock.returnExpressions(): List<FirExpression> = listOfNotNull(statements.lastOrNull() as? FirExpression)
+
+fun FirElement.unwrapWhenSubjectExpression(): FirElement = if (this is FirWhenSubjectExpression) {
+    val whenExpression = whenSubject.whenExpression
+    whenExpression.subjectVariable
+        ?: whenExpression.subject
+        ?: throw IllegalStateException("Subject or subject variable must be not null")
+} else {
+    this
+}
+
+tailrec fun FirElement.unwrapSmartcast(): FirElement = if (this is FirExpressionWithSmartcast) {
+    originalExpression.unwrapSmartcast()
+} else {
+    this
+}