[SYCL] Add macro to disable SYCL's device copyability checks

sycl/doc/PreprocessorMacros.md

@@ -29,6 +29,15 @@ This file describes macros that have effect on SYCL compiler and run-time.
   Disables all deprecation warnings in SYCL runtime headers, including SYCL
   1.2.1 deprecations.
 
+- **SYCL_DISABLE_DEVICE_COPYABLE_CHECKS**
+
+  Makes `sycl::is_device_copyable_v<T>` report `true` for every type, and
+  disables all diagnostics that the SYCL headers issue when a type does not
+  satisfy the device copyability requirements of the SYCL specification. 
+  Passing an object whose type is not actually device copyable to a device
+  results in undefined behavior. The user takes responsibility for ensuring
+  that every type passed to a device can be copied by the implementation.
+
 - **SYCL_DISABLE_IMAGE_ASPECT_WARNING**
 
   Disables warning diagnostic issued when calling `device::has(aspect::image)`

sycl/include/sycl/detail/is_device_copyable.hpp

@@ -39,8 +39,15 @@ struct is_device_copyable_impl<
     : is_device_copyable<std::remove_cv_t<T>> {};
 } // namespace detail
 
+#ifdef SYCL_DISABLE_DEVICE_COPYABLE_CHECKS
+// The user has opted out of the device copyability checks, and takes
+// responsibility for the copyability of the types they pass to a device. See
+// sycl/doc/PreprocessorMacros.md.
+template <typename T> struct is_device_copyable : std::true_type {};
+#else
 template <typename T>
 struct is_device_copyable : detail::is_device_copyable_impl<T> {};
+#endif
 
 // std::array<T, 0> is implicitly device copyable type.
 template <typename T>

sycl/test/basic_tests/device_copyable_checks_disabled.cpp

@@ -0,0 +1,23 @@
+// RUN: %clangxx -fsycl -fsycl-device-only -fsyntax-only -Xclang -verify=checks-on -Xclang -verify-ignore-unexpected=warning,note %s
+// RUN: %clangxx -fsycl -fsycl-device-only -fsyntax-only -DSYCL_DISABLE_DEVICE_COPYABLE_CHECKS -Xclang -verify=checks-off -Xclang -verify-ignore-unexpected=warning,note %s
+
+// checks-off-no-diagnostics
+
+#include <sycl/detail/core.hpp>
+
+// A user-provided destructor is enough to make this neither device copyable nor
+// eligible for the deprecated trivially-copyable exception.
+struct NotDeviceCopyable {
+  ~NotDeviceCopyable() {}
+};
+
+int main() {
+  NotDeviceCopyable Val;
+  // checks-on-error@*:* {{The specified type is not device copyable}}
+#ifdef SYCL_DISABLE_DEVICE_COPYABLE_CHECKS
+  static_assert(sycl::is_device_copyable_v<NotDeviceCopyable>);
+#else
+  static_assert(!sycl::is_device_copyable_v<NotDeviceCopyable>);
+#endif
+  sycl::queue{}.single_task([=] { (void)Val; });
+}