From fc4ca5bdd8c5a2b37b6efe34a9b32a1bd75c57af Mon Sep 17 00:00:00 2001
From: "Justin M. Keyes" <justinkz@gmail.com>
Date: Tue, 8 Jan 2019 22:00:52 +0100
Subject: [PATCH] CMake: Feature-detect __builtin_{add,sub}_overflow

---
 CMakeLists.txt    | 10 ++++++++++
 src/nvim/assert.h |  9 +++++----
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7e73443ec2..8272a1a469 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -248,6 +248,16 @@ int main(void)
 }
 " HAVE_EXECINFO_BACKTRACE)
 
+check_c_source_compiles("
+int main(void)
+{
+  int a;
+  __builtin_add_overflow(a, a, &a);
+  __builtin_sub_overflow(a, a, &a);
+  return 0;
+}
+" HAVE_BUILTIN_ADD_OVERFLOW)
+
 if(MSVC)
   # XXX: /W4 gives too many warnings. #3241
   add_definitions(/W3 -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_DEPRECATE)
diff --git a/src/nvim/assert.h b/src/nvim/assert.h
index 3f985475a7..29195a49dc 100644
--- a/src/nvim/assert.h
+++ b/src/nvim/assert.h
@@ -122,6 +122,7 @@
 #endif
 
 /// @def STRICT_ADD
+/// @brief Adds (a + b) and stores result in `c`.  Aborts on overflow.
 ///
 /// Requires GCC 5+ and Clang 3.8+
 ///   https://clang.llvm.org/docs/LanguageExtensions.html
@@ -132,8 +133,7 @@
 ///
 /// @param MAX Maximum value of the narrowest type of operand.
 ///            Not used if compiler supports __builtin_add_overflow.
-#if (defined(__clang__) && __has_builtin(__builtin_add_overflow)) \
-  || (__GNUC__ >= 5)
+#if HAVE_BUILTIN_ADD_OVERFLOW
 # define STRICT_ADD(a, b, c, t) \
   do { if (__builtin_add_overflow(a, b, c)) { abort(); } } while (0)
 #else
@@ -141,8 +141,9 @@
   do { *(c) = (t)(a + b); } while (0)
 #endif
 
-#if (defined(__clang__) && __has_builtin(__builtin_sub_overflow)) \
-  || (__GNUC__ >= 5)
+/// @def STRICT_SUB
+/// @brief Subtracts (a - b) and stores result in `c`.  Aborts on overflow.
+#if HAVE_BUILTIN_ADD_OVERFLOW
 # define STRICT_SUB(a, b, c, t) \
   do { if (__builtin_sub_overflow(a, b, c)) { abort(); } } while (0)
 #else