[CUDA] Make unattributed constexpr functions implicitly host+device.

With this patch, by a constexpr function is implicitly host+device
unless:

 a) it's a variadic function (variadic functions are not allowed on the
    device side), or
 b) it's preceeded by a __device__ overload in a system header.

The restriction on overloading __host__ __device__ functions on the
basis of their CUDA attributes remains in place, but we use (b) to allow
us to define __device__ overloads for constexpr functions in cmath,
which would otherwise be __host__ __device__ and thus not overloadable.

You can disable this behavior with -fno-cuda-host-device-constexpr.

Reviewers: tra, rnk, rsmith

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D18380

llvm-svn: 264964

1 files changed, 20 insertions, 0 deletions

diff --git a/clang/test/SemaCUDA/no-host-device-constexpr.cu b/clang/test/SemaCUDA/no-host-device-constexpr.cu
new file mode 100644
index 00000000000..c70d97d61e4
--- /dev/null
+++ b/clang/test/SemaCUDA/no-host-device-constexpr.cu
@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 -std=c++11 -fsyntax-only -fno-cuda-host-device-constexpr -verify %s
+// RUN: %clang_cc1 -std=c++11 -fsyntax-only -fno-cuda-host-device-constexpr -fcuda-is-device -verify %s
+
+#include "Inputs/cuda.h"
+
+// Check that, with -fno-cuda-host-device-constexpr, constexpr functions are
+// host-only, and __device__ constexpr functions are still device-only.
+
+constexpr int f() { return 0; } // expected-note {{not viable}}
+__device__ constexpr int g() { return 0; } // expected-note {{not viable}}
+
+void __device__ foo() {
+  f(); // expected-error {{no matching function}}
+  g();
+}
+
+void __host__ foo() {
+  f();
+  g(); // expected-error {{no matching function}}
+}