From be000059251f574c3c34bf0641d285fd1e99d8e4 Mon Sep 17 00:00:00 2001
From: Felix Thaler <thaler@cscs.ch>
Date: Mon, 8 Jul 2024 13:46:10 +0200
Subject: [PATCH] Fix GT_ASSUME for NVCC and Enable GT_ASSUME on Recent GCC
 Versions (#1789)

- Fixes non-functional `GT_ASSUME` on NVCC due to `__has_builtin(__builtin_assume)` returning 0.
- Adds a test to check correctly defined device-side `GT_ASSUME` on NVCC.
- Enables `GT_ASSUME` based on C++-23 `[[assume(x)]]` on recent versions of GCC.
---
 include/gridtools/common/defs.hpp | 16 ++++++++++++----
 tests/unit_tests/CMakeLists.txt   |  1 +
 tests/unit_tests/test_defs.cpp    | 28 ++++++++++++++++++++++++++++
 3 files changed, 41 insertions(+), 4 deletions(-)
 create mode 100644 tests/unit_tests/test_defs.cpp

diff --git a/include/gridtools/common/defs.hpp b/include/gridtools/common/defs.hpp
index 559dd2253..e901679bc 100644
--- a/include/gridtools/common/defs.hpp
+++ b/include/gridtools/common/defs.hpp
@@ -27,13 +27,21 @@ namespace gridtools {
 #endif
 #endif
 
-#if defined(__has_builtin)
+#if defined(__NVCC__) && defined(__CUDA_ARCH__) && \
+    (__CUDACC_VER_MAJOR__ == 11 && __CUDACC_VER_MINOR__ >= 2 || __CUDACC_VER_MAJOR__ > 11)
+#define GT_ASSUME(x) __builtin_assume(x)
+#endif
+#if !defined(GT_ASSUME) && defined(__has_builtin)
 #if __has_builtin(__builtin_assume)
 #define GT_ASSUME(x) __builtin_assume(x)
-#else
-#define GT_ASSUME(x)
 #endif
-#else
+#if !defined(GT_ASSUME) && defined(__cpp_attributes)
+#if __has_cpp_attribute(assume)
+#define GT_ASSUME(x) [[assume(x)]]
+#endif
+#endif
+#endif
+#ifndef GT_ASSUME
 #define GT_ASSUME(x)
 #endif
 
diff --git a/tests/unit_tests/CMakeLists.txt b/tests/unit_tests/CMakeLists.txt
index 6ed9874d9..df2962f68 100644
--- a/tests/unit_tests/CMakeLists.txt
+++ b/tests/unit_tests/CMakeLists.txt
@@ -36,6 +36,7 @@ function(gridtools_add_unit_test tgt)
 endfunction()
 
 gridtools_check_compilation(test_meta test_meta.cpp)
+gridtools_check_compilation(test_defs test_defs.cpp)
 
 add_subdirectory(common)
 add_subdirectory(sid)
diff --git a/tests/unit_tests/test_defs.cpp b/tests/unit_tests/test_defs.cpp
new file mode 100644
index 000000000..0cd1b9ed9
--- /dev/null
+++ b/tests/unit_tests/test_defs.cpp
@@ -0,0 +1,28 @@
+/*
+ * GridTools
+ *
+ * Copyright (c) 2014-2023, ETH Zurich
+ * All rights reserved.
+ *
+ * Please, refer to the LICENSE file in the root directory.
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <string_view>
+
+#include <boost/preprocessor/stringize.hpp>
+
+#include <gridtools/common/defs.hpp>
+
+#if defined(__NVCC__) && defined(__CUDA_ARCH__) && \
+    (__CUDACC_VER_MAJOR__ == 11 && __CUDACC_VER_MINOR__ >= 2 || __CUDACC__VER_MAJOR__ > 11)
+
+#if !defined(GT_ASSUME)
+#error "GT_ASSUME is undefined"
+#else
+static_assert(std::string_view(BOOST_PP_STRINGIZE(GT_ASSUME(x))) ==
+    std::string_view(BOOST_PP_STRINGIZE(__builtin_assume(x))),
+        BOOST_PP_STRINGIZE(GT_ASSUME(x)) " != " BOOST_PP_STRINGIZE(__builtin_assume(x)));
+#endif
+
+#endif