If an if or do statement always exits, following statements are dead.

pkg/analyzer/lib/src/generated/resolver.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.src.generated.resolver;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
@@ skipping 2061 matching lines @@
       }
       if (element == null) {
         _errorReporter
             .reportErrorForNode(hintCode, name, [library.identifier, nameStr]);
       }
     }
   }
 
   /**
    * Given some [NodeList] of [Statement]s, from either a [Block] or
-   * [SwitchMember], this loops through the list in reverse order searching for statements
-   * after a return, unlabeled break or unlabeled continue statement to mark them as dead code.
+   * [SwitchMember], this loops through the list searching for dead statements.
    *
    * @param statements some ordered list of statements in a [Block] or [SwitchMember]
    */
   void _checkForDeadStatementsInNodeList(NodeList<Statement> statements) {
+    bool statementExits(Statement statement) {
+      if (statement is BreakStatement) {
+        return statement.label == null;
+      } else if (statement is ContinueStatement) {
+        return statement.label == null;
+      }
+      return ExitDetector.exits(statement);
+    }
+
     int size = statements.length;
     for (int i = 0; i < size; i++) {
       Statement currentStatement = statements[i];
       currentStatement?.accept(this);
-      bool returnOrBreakingStatement = currentStatement is ReturnStatement ||
-          (currentStatement is BreakStatement &&
-              currentStatement.label == null) ||
-          (currentStatement is ContinueStatement &&
-              currentStatement.label == null);
-      if (returnOrBreakingStatement && i != size - 1) {
+      if (statementExits(currentStatement) && i != size - 1) {
         Statement nextStatement = statements[i + 1];
         Statement lastStatement = statements[size - 1];
         int offset = nextStatement.offset;
         int length = lastStatement.end - offset;
         _errorReporter.reportErrorForOffset(HintCode.DEAD_CODE, offset, length);
         return;
       }
     }
   }
 
@@ skipping 8863 matching lines @@
       return null;
     }
     if (identical(node.staticElement, variable)) {
       if (node.inSetterContext()) {
         result = true;
       }
     }
     return null;
   }
 }