Index: clang/include/clang/Basic/DiagnosticGroups.td
===================================================================
--- clang/include/clang/Basic/DiagnosticGroups.td
+++ clang/include/clang/Basic/DiagnosticGroups.td
@@ -717,6 +717,7 @@
 def InvalidPPToken : DiagGroup<"invalid-pp-token">;
 def Trigraphs      : DiagGroup<"trigraphs">;
 
+def HiddenReinterpretCast : DiagGroup<"hidden-reinterpret-cast">;
 def UndefinedReinterpretCast : DiagGroup<"undefined-reinterpret-cast">;
 def ReinterpretBaseClass : DiagGroup<"reinterpret-base-class">;
 def Unicode  : DiagGroup<"unicode">;
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -7402,6 +7402,10 @@
   "use 'static_cast' to adjust the pointer correctly while "
   "%select{upcasting|downcasting}0">;
 
+def warn_cxx_functional_style_cast_hidden_reinterpret_cast: Warning<
+  "C++ functional style cast may be a hidden reinterpret cast">,
+  InGroup<HiddenReinterpretCast>, DefaultIgnore;
+
 def err_bad_static_cast_overload : Error<
   "address of overloaded function %0 cannot be static_cast to type %1">;
 
Index: clang/lib/Sema/SemaCast.cpp
===================================================================
--- clang/lib/Sema/SemaCast.cpp
+++ clang/lib/Sema/SemaCast.cpp
@@ -2760,6 +2760,15 @@
         // ... and finally a reinterpret_cast, ignoring const and addr space.
         tcr = TryReinterpretCast(Self, SrcExpr, DestType, /*CStyle*/ true,
                                  OpRange, msg, Kind);
+
+        // If this CXX Functional cast is a reinterpret cast then we have a
+        // potentially hidden reinterpret cast here.
+        if (isValidCast(tcr)) {
+          Self.Diag(
+              OpRange.getBegin(),
+              diag::warn_cxx_functional_style_cast_hidden_reinterpret_cast);
+        }
+
         if (SrcExpr.isInvalid())
           return;
       }
Index: clang/test/SemaCXX/hidden_reinterpret_test.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/hidden_reinterpret_test.cpp
@@ -0,0 +1,64 @@
+// Check that various conversions from integral to pointer to references
+// generate an appropriate hidden-reinterpret-cast diagnostic.
+
+// RUN: %clang_cc1 -verify %s -Whidden-reinterpret-cast
+
+class castee {
+public:
+  int i;
+};
+
+class caster {
+public:
+  caster(castee tbc):
+    i(tbc.i) {}
+private:
+  int i;
+};
+
+int main() {
+  using long_def = long long;
+  using long_ptr = long long*;
+  using long_ref = long long&;
+
+  // Check pointer to int conversion for reinterpret warning.
+  long_ptr ptr = 0x0;
+  long_def new_num = long_def(ptr); // expected-warning {{C++ functional style cast may be a hidden reinterpret cast}}
+
+  // Check int to pointer conversion for reinterpret warning.
+  long_def strange_address  = 0xDEADBEEF;
+  long_ptr strange_ptr = long_ptr(strange_address); // expected-warning {{C++ functional style cast may be a hidden reinterpret cast}}
+
+  // Check pointer to reference conversion for reinterpret warning.
+  long_ptr ptr_to_ref = 0x0;
+  long_ref ref_of_ptr = long_ref(ptr_to_ref); // expected-warning {{C++ functional style cast may be a hidden reinterpret cast}}
+
+  // Check reference to pointer conversion, should not provide a warning
+  long_def to_ref = 50;
+  long_ref ref_to_ptr = to_ref;
+  // "long_ptr(ptr_from_ref)" is synonymous with "long_ptr(&to_ref)" and
+  // should not generate a warning.
+  long_ptr ptr_from_ref = long_ptr(ptr_from_ref);
+
+  // implicit conversions and therefore static_casts, should not generate
+  // warnings.
+  float f = 1.5f;
+  int   i = int(f);
+
+  unsigned long int uli = 50;
+  char                c = char(uli);
+
+  long long int   value = 50;
+  long long int   &iref = value;
+  long long int iNotRef = long_def(iref);
+
+  int         small = 500;
+  long long int big = long_def(small);
+
+  // class conversion test, this will call the constructor of to_static_cast
+  // shouldn't generate a warning.
+  castee c1;
+  caster c2 = caster(c1);
+
+  return 0;
+}
Index: clang/test/SemaCXX/hidden_reinterpret_test_template.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/hidden_reinterpret_test_template.cpp
@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -verify %s -Whidden-reinterpret-cast
+
+template <class T>
+T find(T obj[], T key, unsigned long int size) {
+  using X = decltype(obj[0]);
+  for (T *ix = 0; ix != obj+size; ++ix) {
+    if ((*ix) == key)
+      return X(ix); // expected-warning {{C++ functional style cast may be a hidden reinterpret cast}}
+  }
+  return X(key);
+}
+
+int main(const int argc, const char *argv[]) {
+  int array[] = {0, 1, 2, 3};
+  int *array_ptrs[] = {&(array[0]), &(array[1]), &(array[2]), &(array[3])};
+  int *key = &(array[2]);
+  find<int*>(array_ptrs, key, sizeof(array_ptrs));   // expected-note {{in instantiation of function template specialization 'find<int *>' requested here}}
+  return *key;
+}