bpo-41875: Use __builtin_unreachable when possible (GH-22433)

(cherry picked from commit 24ba3b0df5e5f2f237d7b23b4017ba12f16320ae)

Co-authored-by: Dong-hee Na <donghee.na92@gmail.com>

diff --git a/Include/pymacro.h b/Include/pymacro.h
index 856cae774d61c765ebeb0d75f23cd3deb31b6bc6..202b936d964f00dec2f7cb8a3fc993f1bd6cfc85 100644 (file)
--- a/Include/pymacro.h
+++ b/Include/pymacro.h
@@ -118,7 +118,9 @@
         "We've reached an unreachable state. Anything is possible.\n" \
         "The limits were in our heads all along. Follow your dreams.\n" \
         "https://xkcd.com/2200")
-#elif defined(__GNUC__) || defined(__clang__) || defined(__INTEL_COMPILER)
+#elif defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 5))
+#  define Py_UNREACHABLE() __builtin_unreachable()
+#elif defined(__clang__) || defined(__INTEL_COMPILER)
 #  define Py_UNREACHABLE() __builtin_unreachable()
 #elif defined(_MSC_VER)
 #  define Py_UNREACHABLE() __assume(0)

diff --git a/Misc/NEWS.d/next/Build/2020-09-28-21-56-51.bpo-38249.uzMCaZ.rst b/Misc/NEWS.d/next/Build/2020-09-28-21-56-51.bpo-38249.uzMCaZ.rst
new file mode 100644 (file)
index 0000000..3e409ec
--- /dev/null
+++ b/Misc/NEWS.d/next/Build/2020-09-28-21-56-51.bpo-38249.uzMCaZ.rst
@@ -0,0 +1,2 @@
+Update :c:macro:`Py_UNREACHABLE` to use __builtin_unreachable() if only the
+compiler is able to use it. Patch by Dong-hee Na.