Index: include/clang/Basic/DiagnosticGroups.td
===================================================================
--- include/clang/Basic/DiagnosticGroups.td
+++ include/clang/Basic/DiagnosticGroups.td
@@ -538,6 +538,7 @@
 def CoveredSwitchDefault : DiagGroup<"covered-switch-default">;
 def SwitchBool     : DiagGroup<"switch-bool">;
 def SwitchEnum     : DiagGroup<"switch-enum">;
+def SwitchUnreachable     : DiagGroup<"switch-unreachable">;
 def Switch         : DiagGroup<"switch">;
 def EnumCompareSwitch : DiagGroup<"enum-compare-switch">;
 def EnumCompare       : DiagGroup<"enum-compare", [EnumCompareSwitch]>;
@@ -842,7 +843,7 @@
 // Note that putting warnings in -Wall will not disable them by default. If a
 // warning should be active _only_ when -Wall is passed in, mark it as
 // DefaultIgnore in addition to putting it here.
-def All : DiagGroup<"all", [Most, Parentheses, Switch, SwitchBool]>;
+def All : DiagGroup<"all", [Most, Parentheses, Switch, SwitchBool, SwitchUnreachable]>;
 
 // Warnings that should be in clang-cl /w4.
 def : DiagGroup<"CL4", [All, Extra]>;
Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -8188,6 +8188,8 @@
 def err_default_not_in_switch : Error<
   "'default' statement not in switch statement">;
 def err_case_not_in_switch : Error<"'case' statement not in switch statement">;
+def warn_unreachable_stmt_in_switch : Warning<
+  "statement will be never executed">, InGroup<SwitchUnreachable>, DefaultIgnore;
 def warn_bool_switch_condition : Warning<
   "switch condition has boolean value">, InGroup<SwitchBool>;
 def warn_case_value_overflow : Warning<
Index: lib/Sema/SemaStmt.cpp
===================================================================
--- lib/Sema/SemaStmt.cpp
+++ lib/Sema/SemaStmt.cpp
@@ -861,6 +861,20 @@
   typedef std::vector<std::pair<llvm::APSInt, CaseStmt*> > CaseRangesTy;
   CaseRangesTy CaseRanges;
 
+  if (CompoundStmt *CS = dyn_cast<CompoundStmt>(BodyStmt)) {
+    for (auto It = CS->body_begin(); It != CS->body_end(); ++It) {
+      auto *S = *It;
+      if (isa<LabelStmt>(S) || isa<CaseStmt>(S) || isa<DefaultStmt>(S))
+        break;
+      Diag(S->getBeginLoc(), diag::warn_unreachable_stmt_in_switch);
+    }
+  } else if (isa<LabelStmt>(BodyStmt) || isa<CaseStmt>(BodyStmt) ||
+             isa<DefaultStmt>(BodyStmt)) {
+    // No warning
+  } else {
+    Diag(BodyStmt->getBeginLoc(), diag::warn_unreachable_stmt_in_switch);
+  }
+
   DefaultStmt *TheDefaultStmt = nullptr;
 
   bool CaseListIsErroneous = false;
Index: test/Sema/switch_unreachable.c
===================================================================
--- test/Sema/switch_unreachable.c
+++ test/Sema/switch_unreachable.c
@@ -0,0 +1,143 @@
+// RUN: %clang_cc1 -x c -fsyntax-only -verify -Wswitch-unreachable %s
+// RUN: %clang_cc1 -x c -fsyntax-only -verify -Wall %s
+
+void g(int x);
+
+void foo(int x) {
+  int b = 0;
+  switch (x) {
+  label:
+  case 4:
+    break;
+  default:
+    return;
+  }
+
+  switch (x) {
+    x++; // expected-warning {{statement will be never executed}}
+  label2:
+  case 4:
+    break;
+  default:
+    return;
+  }
+
+  switch (x) {
+  label3:
+    x++;
+  case 4:
+    break;
+  default:
+    return;
+  }
+
+  switch (x) {
+  case 4:
+    return;
+  }
+
+  switch (x) {
+    b = x; // expected-warning {{statement will be never executed}}
+  case 7:
+    g(b);
+    break;
+  }
+
+  switch (x) {
+    break; // expected-warning {{statement will be never executed}}
+  case 7:
+    break;
+  }
+
+  switch (x) {
+    return; // expected-warning {{statement will be never executed}}
+  case 7:
+    break;
+  }
+
+  switch (x) {
+    x++;  // expected-warning {{statement will be never executed}}
+    g(x); // expected-warning {{statement will be never executed}}
+  case 7:
+    break;
+  }
+
+  switch (x) {
+    x++; // expected-warning {{statement will be never executed}}
+  label4:
+    g(x);
+  case 7:
+    break;
+  }
+
+  switch (x) {
+    g(x); // expected-warning {{statement will be never executed}}
+  case 1:
+    break;
+  case 2:
+    break;
+  }
+
+  switch (x) {
+    g(x); // expected-warning {{statement will be never executed}}
+  case 1:
+  case 2:
+  case 3:
+    break;
+  }
+
+  switch (x) {
+  case 1:
+    break;
+  case 2:
+    break;
+  }
+
+  switch (x) {
+  case 1:
+    break;
+  default:
+    break;
+  }
+
+  switch (x) {
+    b = x; // expected-warning {{statement will be never executed}}
+  }
+
+  switch (x) {
+    g(x); // expected-warning {{statement will be never executed}}
+  }
+
+  switch (x)
+    b = x; // expected-warning {{statement will be never executed}}
+
+  switch (x)
+    g(x); // expected-warning {{statement will be never executed}}
+
+  switch (x)
+  label5:
+    g(x);
+
+  switch (x) {
+  label6:
+    g(x);
+  }
+
+  switch (x)
+  case 5:
+    g(x);
+
+  switch (x) {
+  case 5:
+    g(x);
+  }
+
+  switch (x)
+  default:
+    g(x);
+
+  switch (x) {
+  case 5:
+    g(x);
+  }
+}
Index: test/SemaCXX/switch_unreachable.cpp
===================================================================
--- test/SemaCXX/switch_unreachable.cpp
+++ test/SemaCXX/switch_unreachable.cpp
@@ -0,0 +1,143 @@
+// RUN: %clang_cc1 -x c++ -fsyntax-only -verify -Wswitch-unreachable %s
+// RUN: %clang_cc1 -x c++ -fsyntax-only -verify -Wall %s
+
+void g(int x);
+
+void foo(int x) {
+  int b = 0;
+  switch (x) {
+  label:
+  case 4:
+    break;
+  default:
+    return;
+  }
+
+  switch (x) {
+    x++; // expected-warning {{statement will be never executed}}
+  label2:
+  case 4:
+    break;
+  default:
+    return;
+  }
+
+  switch (x) {
+  label3:
+    x++;
+  case 4:
+    break;
+  default:
+    return;
+  }
+
+  switch (x) {
+  case 4:
+    return;
+  }
+
+  switch (x) {
+    b = x; // expected-warning {{statement will be never executed}}
+  case 7:
+    g(b);
+    break;
+  }
+
+  switch (x) {
+    break; // expected-warning {{statement will be never executed}}
+  case 7:
+    break;
+  }
+
+  switch (x) {
+    return; // expected-warning {{statement will be never executed}}
+  case 7:
+    break;
+  }
+
+  switch (x) {
+    x++;  // expected-warning {{statement will be never executed}}
+    g(x); // expected-warning {{statement will be never executed}}
+  case 7:
+    break;
+  }
+
+  switch (x) {
+    x++; // expected-warning {{statement will be never executed}}
+  label4:
+    g(x);
+  case 7:
+    break;
+  }
+
+  switch (x) {
+    g(x); // expected-warning {{statement will be never executed}}
+  case 1:
+    break;
+  case 2:
+    break;
+  }
+
+  switch (x) {
+    g(x); // expected-warning {{statement will be never executed}}
+  case 1:
+  case 2:
+  case 3:
+    break;
+  }
+
+  switch (x) {
+  case 1:
+    break;
+  case 2:
+    break;
+  }
+
+  switch (x) {
+  case 1:
+    break;
+  default:
+    break;
+  }
+
+  switch (x) {
+    b = x; // expected-warning {{statement will be never executed}}
+  }
+
+  switch (x) {
+    g(x); // expected-warning {{statement will be never executed}}
+  }
+
+  switch (x)
+    b = x; // expected-warning {{statement will be never executed}}
+
+  switch (x)
+    g(x); // expected-warning {{statement will be never executed}}
+
+  switch (x)
+  label5:
+    g(x);
+
+  switch (x) {
+  label6:
+    g(x);
+  }
+
+  switch (x)
+  case 5:
+    g(x);
+
+  switch (x) {
+  case 5:
+    g(x);
+  }
+
+  switch (x)
+  default:
+    g(x);
+
+  switch (x) {
+  default:
+    g(x);
+  }
+}