Index: include/clang/Basic/LangOptions.def
===================================================================
--- include/clang/Basic/LangOptions.def
+++ include/clang/Basic/LangOptions.def
@@ -175,6 +175,7 @@
 LANGOPT(CUDADisableTargetCallChecks, 1, 0, "Disable checks for call targets (host, device, etc.)")
 LANGOPT(CUDATargetOverloads, 1, 0, "Enable function overloads based on CUDA target attributes")
 LANGOPT(CUDAAllowVariadicFunctions, 1, 0, "Allow variadic functions in CUDA device code")
+LANGOPT(CUDARelaxedConstexpr, 1, 0, "Treat constexpr functions as __host__ __device__")
 
 LANGOPT(AssumeSaneOperatorNew , 1, 1, "implicit __attribute__((malloc)) for C++'s new operators")
 LANGOPT(SizedDeallocation , 1, 0, "enable sized deallocation functions")
Index: include/clang/Driver/CC1Options.td
===================================================================
--- include/clang/Driver/CC1Options.td
+++ include/clang/Driver/CC1Options.td
@@ -699,6 +699,8 @@
   HelpText<"Enable function overloads based on CUDA target attributes.">;
 def fcuda_allow_variadic_functions : Flag<["-"], "fcuda-allow-variadic-functions">,
   HelpText<"Allow variadic functions in CUDA device code.">;
+def fcuda_relaxed_constexpr : Flag<["-"], "fcuda-relaxed-constexpr">,
+  HelpText<"Treat constexpr functions as __host__ __device__.">;
 
 //===----------------------------------------------------------------------===//
 // OpenMP Options
Index: lib/Driver/Tools.cpp
===================================================================
--- lib/Driver/Tools.cpp
+++ lib/Driver/Tools.cpp
@@ -3594,6 +3594,7 @@
     CmdArgs.push_back(Args.MakeArgString(AuxToolChain->getTriple().str()));
     CmdArgs.push_back("-fcuda-target-overloads");
     CmdArgs.push_back("-fcuda-disable-target-call-checks");
+    CmdArgs.push_back("-fcuda-relaxed-constexpr");
   }
 
   if (Triple.isOSWindows() && (Triple.getArch() == llvm::Triple::arm ||
Index: lib/Frontend/CompilerInvocation.cpp
===================================================================
--- lib/Frontend/CompilerInvocation.cpp
+++ lib/Frontend/CompilerInvocation.cpp
@@ -1569,6 +1569,9 @@
   if (Args.hasArg(OPT_fcuda_allow_variadic_functions))
     Opts.CUDAAllowVariadicFunctions = 1;
 
+  if (Args.hasArg(OPT_fcuda_relaxed_constexpr))
+    Opts.CUDARelaxedConstexpr = 1;
+
   if (Opts.ObjC1) {
     if (Arg *arg = Args.getLastArg(OPT_fobjc_runtime_EQ)) {
       StringRef value = arg->getValue();
Index: lib/Sema/SemaDecl.cpp
===================================================================
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -8006,6 +8006,15 @@
   // Handle attributes.
   ProcessDeclAttributes(S, NewFD, D);
 
+  // With -fcuda-relaxed-constexpr, constexpr functions are treated as
+  // implicitly __host__ __device__.  Device-side variadic functions are not
+  // allowed, so we just treat those as host-only.
+  if (getLangOpts().CUDA && NewFD->isConstexpr() && !NewFD->isVariadic() &&
+      getLangOpts().CUDARelaxedConstexpr) {
+    NewFD->addAttr(CUDAHostAttr::CreateImplicit(Context));
+    NewFD->addAttr(CUDADeviceAttr::CreateImplicit(Context));
+  }
+
   if (getLangOpts().OpenCL) {
     // OpenCL v1.1 s6.5: Using an address space qualifier in a function return
     // type declaration will generate a compilation error.
Index: lib/Sema/SemaOverload.cpp
===================================================================
--- lib/Sema/SemaOverload.cpp
+++ lib/Sema/SemaOverload.cpp
@@ -1126,13 +1126,10 @@
 
     assert((OldTarget != CFT_InvalidTarget) && "Unexpected invalid target.");
 
-    // Don't allow mixing of HD with other kinds. This guarantees that
-    // we have only one viable function with this signature on any
-    // side of CUDA compilation .
-    // __global__ functions can't be overloaded based on attribute
-    // difference because, like HD, they also exist on both sides.
-    if ((NewTarget == CFT_HostDevice) || (OldTarget == CFT_HostDevice) ||
-        (NewTarget == CFT_Global) || (OldTarget == CFT_Global))
+    // Don't allow __global__ functions to be overloaded with other functions,
+    // based solely on their CUDA attributes. This guarantees that we have only
+    // one viable function with this signature on any side of CUDA compilation.
+    if ((NewTarget == CFT_Global) || (OldTarget == CFT_Global))
       return false;
 
     // Allow overloading of functions with same signature, but
Index: test/SemaCUDA/function-overload.cu
===================================================================
--- test/SemaCUDA/function-overload.cu
+++ test/SemaCUDA/function-overload.cu
@@ -49,22 +49,18 @@
 __host__ HostReturnTy dh() { return HostReturnTy(); }
 __device__ DeviceReturnTy dh() { return DeviceReturnTy(); }
 
-// H/HD and D/HD are not allowed.
-__host__ __device__ int hdh() { return 0; } // expected-note {{previous definition is here}}
-__host__ int hdh() { return 0; }            // expected-error {{redefinition of 'hdh'}}
+// H/HD and D/HD are also OK.
+__host__ __device__ HostDeviceReturnTy hdh() { return HostDeviceReturnTy(); }
+__host__ HostReturnTy hdh() { return HostReturnTy(); }
 
-__host__ int hhd() { return 0; }            // expected-note {{previous definition is here}}
-__host__ __device__ int hhd() { return 0; } // expected-error {{redefinition of 'hhd'}}
-// expected-warning@-1 {{attribute declaration must precede definition}}
-// expected-note@-3 {{previous definition is here}}
+__host__ HostReturnTy hhd() { return HostReturnTy(); }
+__host__ __device__ HostDeviceReturnTy hhd() { return HostDeviceReturnTy(); }
 
-__host__ __device__ int hdd() { return 0; } // expected-note {{previous definition is here}}
-__device__ int hdd() { return 0; }          // expected-error {{redefinition of 'hdd'}}
+__host__ __device__ HostDeviceReturnTy hdd() { return HostDeviceReturnTy(); }
+__device__ DeviceReturnTy hdd() { return DeviceReturnTy(); }
 
-__device__ int dhd() { return 0; }          // expected-note {{previous definition is here}}
-__host__ __device__ int dhd() { return 0; } // expected-error {{redefinition of 'dhd'}}
-// expected-warning@-1 {{attribute declaration must precede definition}}
-// expected-note@-3 {{previous definition is here}}
+__device__ DeviceReturnTy dhd() { return DeviceReturnTy(); }
+__host__ __device__ HostDeviceReturnTy dhd() { return HostDeviceReturnTy(); }
 
 // Same tests for extern "C" functions.
 extern "C" __host__ int chh() { return 0; } // expected-note {{previous definition is here}}
@@ -74,14 +70,12 @@
 extern "C" __device__ DeviceReturnTy cdh() { return DeviceReturnTy(); }
 extern "C" __host__ HostReturnTy cdh() { return HostReturnTy(); }
 
-// H/HD and D/HD overloading is not allowed.
-extern "C" __host__ __device__ int chhd1() { return 0; } // expected-note {{previous definition is here}}
-extern "C" __host__ int chhd1() { return 0; }            // expected-error {{redefinition of 'chhd1'}}
+// H/HD and D/HD overloading is OK.
+extern "C" __host__ __device__ HostDeviceReturnTy chhd() { return HostDeviceReturnTy(); }
+extern "C" __host__ HostReturnTy chhd() { return HostReturnTy(); }
 
-extern "C" __host__ int chhd2() { return 0; }            // expected-note {{previous definition is here}}
-extern "C" __host__ __device__ int chhd2() { return 0; } // expected-error {{redefinition of 'chhd2'}}
-// expected-warning@-1 {{attribute declaration must precede definition}}
-// expected-note@-3 {{previous definition is here}}
+extern "C" __host__ __device__ HostDeviceReturnTy chdd() { return HostDeviceReturnTy(); }
+extern "C" __device__ DeviceReturnTy chdd() { return DeviceReturnTy(); }
 
 // Helper functions to verify calling restrictions.
 __device__ DeviceReturnTy d() { return DeviceReturnTy(); }
@@ -128,6 +122,16 @@
   HostFnPtr fp_cdh = cdh;
   HostReturnTy ret_cdh = cdh();
 
+  HostFnPtr fp_hdh = hdh;
+  HostReturnTy ret_hdh = hdh();
+  HostFnPtr fp_chhd = chhd;
+  HostReturnTy ret_chhd = chhd();
+
+  HostDeviceFnPtr fp_hdd = hdd;
+  HostDeviceReturnTy ret_hdd = hdd();
+  HostDeviceFnPtr fp_chdd = chdd;
+  HostDeviceReturnTy ret_chdd = chdd();
+
   GlobalFnPtr fp_g = g;
   g(); // expected-error {{call to global function g not configured}}
   g<<<0, 0>>>();
@@ -149,6 +153,16 @@
   DeviceFnPtr fp_cdh = cdh;
   DeviceReturnTy ret_cdh = cdh();
 
+  HostDeviceFnPtr fp_hdh = hdh;
+  HostDeviceReturnTy ret_hdh = hdh();
+  HostDeviceFnPtr fp_chhd = chhd;
+  HostDeviceReturnTy ret_chhd = chhd();
+
+  DeviceFnPtr fp_hdd = hdd;
+  DeviceReturnTy ret_hdd = hdd();
+  DeviceFnPtr fp_chdd = chdd;
+  DeviceReturnTy ret_chdd = chdd();
+
   GlobalFnPtr fp_g = g; // expected-error {{reference to __global__ function 'g' in __device__ function}}
   g(); // expected-error {{no matching function for call to 'g'}}
   g<<<0,0>>>(); // expected-error {{reference to __global__ function 'g' in __device__ function}}
@@ -170,6 +184,16 @@
   DeviceFnPtr fp_cdh = cdh;
   DeviceReturnTy ret_cdh = cdh();
 
+  HostDeviceFnPtr fp_hdh = hdh;
+  HostDeviceReturnTy ret_hdh = hdh();
+  HostDeviceFnPtr fp_chhd = chhd;
+  HostDeviceReturnTy ret_chhd = chhd();
+
+  DeviceFnPtr fp_hdd = hdd;
+  DeviceReturnTy ret_hdd = hdd();
+  DeviceFnPtr fp_chdd = chdd;
+  DeviceReturnTy ret_chdd = chdd();
+
   GlobalFnPtr fp_g = g; // expected-error {{reference to __global__ function 'g' in __global__ function}}
   g(); // expected-error {{no matching function for call to 'g'}}
   g<<<0,0>>>(); // expected-error {{reference to __global__ function 'g' in __global__ function}}
@@ -203,6 +227,30 @@
   CurrentFnPtr fp_cdh = cdh;
   CurrentReturnTy ret_cdh = cdh();
 
+  // HDOrHostFoo is HostFoo if we're doing host compilation, and HDFoo
+  // otherwise.
+#ifdef __CUDA_ARCH__
+  typedef HostDeviceReturnTy HDOrHostReturnTy;
+  typedef HostDeviceFnPtr HDOrHostFnPtr;
+  typedef DeviceReturnTy HDOrDeviceReturnTy;
+  typedef DeviceFnPtr HDOrDeviceFnPtr;
+#else
+  typedef HostReturnTy HDOrHostReturnTy;
+  typedef HostFnPtr HDOrHostFnPtr;
+  typedef HostDeviceReturnTy HDOrDeviceReturnTy;
+  typedef HostDeviceFnPtr HDOrDeviceFnPtr;
+#endif
+
+  HDOrHostFnPtr fp_hdh = hdh;
+  HDOrHostReturnTy ret_hdh = hdh();
+  HDOrHostFnPtr fp_chhd = chhd;
+  HDOrHostReturnTy ret_chhd = chhd();
+
+  HDOrDeviceFnPtr fp_hdd = hdd;
+  HDOrDeviceReturnTy ret_hdd = hdd();
+  HDOrDeviceFnPtr fp_chdd = chdd;
+  HDOrDeviceReturnTy ret_chdd = chdd();
+
   GlobalFnPtr fp_g = g;
 #if defined(__CUDA_ARCH__)
   // expected-error@-2 {{reference to __global__ function 'g' in __host__ __device__ function}}
@@ -243,31 +291,31 @@
   __host__ __device__ ~d_hd() {}
 };
 
-// Mixing H/D and HD is not allowed.
+// Mixing H/D and HD is OK.
 struct d_dhhd {
   __device__ ~d_dhhd() {}
-  __host__ ~d_dhhd() {} // expected-note {{previous declaration is here}}
-  __host__ __device__ ~d_dhhd() {} // expected-error {{destructor cannot be redeclared}}
+  __host__ ~d_dhhd() {}
+  __host__ __device__ ~d_dhhd() {}
 };
 
 struct d_hhd {
-  __host__ ~d_hhd() {} // expected-note {{previous declaration is here}}
-  __host__ __device__ ~d_hhd() {} // expected-error {{destructor cannot be redeclared}}
+  __host__ ~d_hhd() {}
+  __host__ __device__ ~d_hhd() {}
 };
 
 struct d_hdh {
-  __host__ __device__ ~d_hdh() {} // expected-note {{previous declaration is here}}
-  __host__ ~d_hdh() {} // expected-error {{destructor cannot be redeclared}}
+  __host__ __device__ ~d_hdh() {}
+  __host__ ~d_hdh() {}
 };
 
 struct d_dhd {
-  __device__ ~d_dhd() {} // expected-note {{previous declaration is here}}
-  __host__ __device__ ~d_dhd() {} // expected-error {{destructor cannot be redeclared}}
+  __device__ ~d_dhd() {}
+  __host__ __device__ ~d_dhd() {}
 };
 
 struct d_hdd {
-  __host__ __device__ ~d_hdd() {} // expected-note {{previous declaration is here}}
-  __device__ ~d_hdd() {} // expected-error {{destructor cannot be redeclared}}
+  __host__ __device__ ~d_hdd() {}
+  __device__ ~d_hdd() {}
 };
 
 // Test overloading of member functions
@@ -288,23 +336,23 @@
 };
 
 struct m_hhd {
-  __host__ void operator delete(void *ptr) {} // expected-note {{previous declaration is here}}
-  __host__ __device__ void operator delete(void *ptr) {} // expected-error {{class member cannot be redeclared}}
+  __host__ void operator delete(void *ptr) {}
+  __host__ __device__ void operator delete(void *ptr) {}
 };
 
 struct m_hdh {
-  __host__ __device__ void operator delete(void *ptr) {} // expected-note {{previous declaration is here}}
-  __host__ void operator delete(void *ptr) {} // expected-error {{class member cannot be redeclared}}
+  __host__ __device__ void operator delete(void *ptr) {}
+  __host__ void operator delete(void *ptr) {}
 };
 
 struct m_dhd {
-  __device__ void operator delete(void *ptr) {} // expected-note {{previous declaration is here}}
-  __host__ __device__ void operator delete(void *ptr) {} // expected-error {{class member cannot be redeclared}}
+  __device__ void operator delete(void *ptr) {}
+  __host__ __device__ void operator delete(void *ptr) {}
 };
 
 struct m_hdd {
-  __host__ __device__ void operator delete(void *ptr) {} // expected-note {{previous declaration is here}}
-  __device__ void operator delete(void *ptr) {} // expected-error {{class member cannot be redeclared}}
+  __host__ __device__ void operator delete(void *ptr) {}
+  __device__ void operator delete(void *ptr) {}
 };
 
 // __global__ functions can't be overloaded based on attribute
Index: test/SemaCUDA/relaxed-constexpr.cu
===================================================================
--- /dev/null
+++ test/SemaCUDA/relaxed-constexpr.cu
@@ -0,0 +1,23 @@
+// RUN: %clang_cc1 -std=c++11 -fsyntax-only -verify %s -fcuda-target-overloads -fcuda-relaxed-constexpr
+// RUN: %clang_cc1 -std=c++11 -fsyntax-only -verify %s -fcuda-target-overloads -fcuda-relaxed-constexpr -fcuda-is-device
+
+// expected-no-diagnostics
+
+#include "Inputs/cuda.h"
+
+static __device__ void f1();
+constexpr void f1();
+
+__device__ void f2();
+static constexpr void f2();
+
+// Different potential error depending on the order of declaration.
+constexpr void f3();
+static __device__ void f3();
+
+static constexpr void f4();
+__device__ void f4();
+
+// Variadic device functions are not allowed, so this is just treated as
+// host-only.
+constexpr void variadic(const char*, ...);