[SYCL] Add workaround for undeterminable constexpr lambda return (#19191)

Due to a bug in the compiler, certain conditions give false compiler
errors for return types of constexpr lambdas. This commit implements
workarounds for cases that affect the SYCL headers when using
properties.

Signed-off-by: Larsen, Steffen <[email protected]>

Author: steffenlarsen

sycl/include/sycl/ext/oneapi/properties/properties.hpp

@@ -48,7 +48,7 @@ using properties_t =
     properties<detail::properties_type_list<PropertyValueTs...>>;
 
 template <typename... property_tys>
-inline constexpr bool properties_are_unique = []() constexpr {
+inline constexpr bool properties_are_unique = []() constexpr -> bool {
   if constexpr (sizeof...(property_tys) == 0) {
     return true;
   } else {
@@ -64,7 +64,7 @@ inline constexpr bool properties_are_unique = []() constexpr {
 }();
 
 template <typename... property_tys>
-inline constexpr bool properties_are_sorted = []() constexpr {
+inline constexpr bool properties_are_sorted = []() constexpr -> bool {
   if constexpr (sizeof...(property_tys) == 0) {
     return true;
   } else {

sycl/include/sycl/ext/oneapi/properties/property.hpp

@@ -258,7 +258,7 @@ struct property_base : property_key_tag<property_key_t> {
   // Temporary, to ensure new code matches previous behavior and to catch any
   // silly copy-paste mistakes. MSVC can't compile it, but linux-only is
   // enough for this temporary check.
-  static_assert([]() constexpr {
+  static_assert([]() constexpr -> bool {
     if constexpr (std::is_same_v<property_t, key_t>)
       // key_t is incomplete at this point for runtime properties.
       return true;

sycl/test/regression/grf_properties_wa.cpp

@@ -0,0 +1,15 @@
+// RUN: %clangxx -fsycl -fsyntax-only %s
+
+// Test for a workaround to a bug in clang causing some constexpr lambda
+// expressions to not be identified as returning a bool.
+
+#include <sycl/detail/kernel_properties.hpp>
+#include <sycl/ext/intel/experimental/grf_size_properties.hpp>
+#include <sycl/sycl.hpp>
+
+int main() {
+  if constexpr (false) {
+    sycl::ext::oneapi::experimental::properties prop{
+        sycl::ext::intel::experimental::grf_size<256>};
+  }
+}