From: mpage <mpage@meta.com>
Date: Wed, 9 Apr 2025 17:34:12 +0000 (-0700)
Subject: gh-129987: Disable GCC SLP autovectorization for the interpreter loop on x86-64 ... 
X-Git-Tag: v3.14.0b1~559
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=1f5682f3a27516833f7c317707dd359280dba6e7;p=thirdparty%2FPython%2Fcpython.git

gh-129987: Disable GCC SLP autovectorization for the interpreter loop on x86-64 (#132295)

The SLP autovectorizer can cause poor code generation for opcode dispatch, negating any benefit we get from vectorization elsewhere in the interpreter loop.
---

diff --git a/Python/ceval.c b/Python/ceval.c
index a59b2b7a1686..47d068edac27 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -948,7 +948,18 @@ _PyObjectArray_Free(PyObject **array, PyObject **scratch)
 #include "generated_cases.c.h"
 #endif
 
-PyObject* _Py_HOT_FUNCTION
+#if (defined(__GNUC__) && !defined(__clang__)) && defined(__x86_64__)
+/*
+ * gh-129987: The SLP autovectorizer can cause poor code generation for opcode
+ * dispatch, negating any benefit we get from vectorization elsewhere in the
+ * interpreter loop.
+ */
+#define DONT_SLP_VECTORIZE __attribute__((optimize ("no-tree-slp-vectorize")))
+#else
+#define DONT_SLP_VECTORIZE
+#endif
+
+PyObject* _Py_HOT_FUNCTION DONT_SLP_VECTORIZE
 _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int throwflag)
 {
     _Py_EnsureTstateNotNULL(tstate);