Index: clang/lib/AST/Interp/ByteCodeExprGen.cpp
===================================================================
--- clang/lib/AST/Interp/ByteCodeExprGen.cpp
+++ clang/lib/AST/Interp/ByteCodeExprGen.cpp
@@ -192,6 +192,15 @@
       return true;
     return this->emitNull(classifyPrim(CE->getType()), CE);
 
+  case CK_PointerToIntegral: {
+    // TODO: Discard handling.
+    if (!this->visit(SubExpr))
+      return false;
+
+    PrimType T = classifyPrim(CE->getType());
+    return this->emitCastPointerIntegral(T, CE);
+  }
+
   case CK_ArrayToPointerDecay:
   case CK_AtomicToNonAtomic:
   case CK_ConstructorConversion:
Index: clang/lib/AST/Interp/Interp.h
===================================================================
--- clang/lib/AST/Interp/Interp.h
+++ clang/lib/AST/Interp/Interp.h
@@ -108,6 +108,10 @@
 /// Checks that all fields are initialized after a constructor call.
 bool CheckCtorCall(InterpState &S, CodePtr OpPC, const Pointer &This);
 
+/// Checks if reinterpret casts are legal in the current context.
+bool CheckPotentialReinterpretCast(InterpState &S, CodePtr OpPC,
+                                   const Pointer &Ptr);
+
 /// Checks if the shift operation is legal.
 template <typename LT, typename RT>
 bool CheckShift(InterpState &S, CodePtr OpPC, const LT &LHS, const RT &RHS,
@@ -1571,6 +1575,17 @@
   }
 }
 
+template <PrimType Name, class T = typename PrimConv<Name>::T>
+bool CastPointerIntegral(InterpState &S, CodePtr OpPC) {
+  const Pointer &Ptr = S.Stk.pop<Pointer>();
+
+  if (!CheckPotentialReinterpretCast(S, OpPC, Ptr))
+    return false;
+
+  S.Stk.push<T>(T::from(Ptr.getIntegerRepresentation()));
+  return true;
+}
+
 //===----------------------------------------------------------------------===//
 // Zero, Nullptr
 //===----------------------------------------------------------------------===//
Index: clang/lib/AST/Interp/Interp.cpp
===================================================================
--- clang/lib/AST/Interp/Interp.cpp
+++ clang/lib/AST/Interp/Interp.cpp
@@ -519,6 +519,17 @@
   return true;
 }
 
+bool CheckPotentialReinterpretCast(InterpState &S, CodePtr OpPC,
+                                   const Pointer &Ptr) {
+  if (!S.inConstantContext())
+    return true;
+
+  const SourceInfo &E = S.Current->getSource(OpPC);
+  S.CCEDiag(E, diag::note_constexpr_invalid_cast)
+      << 2 << S.getLangOpts().CPlusPlus;
+  return false;
+}
+
 bool CastFP(InterpState &S, CodePtr OpPC, const llvm::fltSemantics *Sem,
             llvm::RoundingMode RM) {
   Floating F = S.Stk.pop<Floating>();
Index: clang/lib/AST/Interp/Opcodes.td
===================================================================
--- clang/lib/AST/Interp/Opcodes.td
+++ clang/lib/AST/Interp/Opcodes.td
@@ -590,6 +590,12 @@
   let HasGroup = 1;
 }
 
+def CastPointerIntegral : Opcode {
+  let Types = [AluTypeClass];
+  let Args = [];
+  let HasGroup = 1;
+}
+
 //===----------------------------------------------------------------------===//
 // Comparison opcodes.
 //===----------------------------------------------------------------------===//
Index: clang/lib/AST/Interp/Pointer.h
===================================================================
--- clang/lib/AST/Interp/Pointer.h
+++ clang/lib/AST/Interp/Pointer.h
@@ -82,6 +82,10 @@
   /// Converts the pointer to a string usable in diagnostics.
   std::string toDiagnosticString(const ASTContext &Ctx) const;
 
+  unsigned getIntegerRepresentation() const {
+    return reinterpret_cast<uintptr_t>(Pointee) + Offset;
+  }
+
   /// Converts the pointer to an APValue that is an rvalue.
   APValue toRValue(const Context &Ctx) const;
 
Index: clang/test/AST/Interp/literals.cpp
===================================================================
--- clang/test/AST/Interp/literals.cpp
+++ clang/test/AST/Interp/literals.cpp
@@ -6,6 +6,8 @@
 #define INT_MIN (~__INT_MAX__)
 #define INT_MAX __INT_MAX__
 
+typedef __INTPTR_TYPE__ intptr_t;
+
 
 static_assert(true, "");
 static_assert(false, ""); // expected-error{{failed}} ref-error{{failed}}
@@ -1008,3 +1010,15 @@
   static_assert(heh(2) == 'h', "");
 #endif
 }
+
+namespace PointerCasts {
+  constexpr int M = 10;
+  constexpr const int *P = &M;
+  constexpr intptr_t A = (intptr_t)P; // ref-error {{must be initialized by a constant expression}} \
+                                      // ref-note {{cast that performs the conversions of a reinterpret_cast}} \
+                                      // expected-error {{must be initialized by a constant expression}} \
+                                      // expected-note {{cast that performs the conversions of a reinterpret_cast}}
+
+  int array[(long)(char*)0]; // ref-warning {{variable length array folded to constant array}} \
+                             // expected-warning {{variable length array folded to constant array}}
+}