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

miss-islington · corona10 · web-flow · commit cca896e13b23 · 2020-09-28T15:16:24.000-07:00
(cherry picked from commit 24ba3b0) Co-authored-by: Dong-hee Na <donghee.na92@gmail.com>
diff --git 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
@@ -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.

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+Update :c:macro:`Py_UNREACHABLE` to use __builtin_unreachable() if only the
	`2`	`+compiler is able to use it. Patch by Dong-hee Na.`