From: INADA Naoki <methane@users.noreply.github.com>
Date: Wed, 7 Feb 2018 10:09:36 +0000 (+0900)
Subject: bpo-32616: Disable computed gotos by default for clang < 5 (GH-5574)
X-Git-Tag: v2.7.15rc1~59
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2942b909d9a428e6683d90b3436cfa4a81bd5d8a;p=thirdparty%2FPython%2Fcpython.git

bpo-32616: Disable computed gotos by default for clang < 5 (GH-5574)
---

diff --git a/Misc/NEWS.d/next/Build/2018-02-07-11-24-38.bpo-32616.o7mFJ3.rst b/Misc/NEWS.d/next/Build/2018-02-07-11-24-38.bpo-32616.o7mFJ3.rst
new file mode 100644
index 000000000000..cdddc2f2d909
--- /dev/null
+++ b/Misc/NEWS.d/next/Build/2018-02-07-11-24-38.bpo-32616.o7mFJ3.rst
@@ -0,0 +1,2 @@
+Disable computed gotos by default for clang < 5.0. It caused significant
+performance regression.
diff --git a/Python/ceval.c b/Python/ceval.c
index 4e4adc2d63dc..bae158dc1402 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -689,11 +689,19 @@ PyObject *
 PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
 {
 #ifdef DYNAMIC_EXECUTION_PROFILE
-  #undef USE_COMPUTED_GOTOS
+    #undef USE_COMPUTED_GOTOS
 #endif
 #ifdef HAVE_COMPUTED_GOTOS
     #ifndef USE_COMPUTED_GOTOS
-    #define USE_COMPUTED_GOTOS 1
+        #if defined(__clang__) && (__clang_major__ < 5)
+            /* Computed gotos caused significant performance regression
+             * with clang < 5.0.
+             * https://bugs.python.org/issue32616
+             */
+            #define USE_COMPUTED_GOTOS 0
+        #else
+            #define USE_COMPUTED_GOTOS 1
+        #endif
     #endif
 #else
     #if defined(USE_COMPUTED_GOTOS) && USE_COMPUTED_GOTOS