From fdc008138e50eab987217b79ddac303877e81869 Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
 <31488909+miss-islington@users.noreply.github.com>
Date: Thu, 30 Jun 2022 09:11:05 -0700
Subject: [PATCH] gh-91719: Reload opcode on unknown error so that C can
 optimize the dispatching in ceval.c (GH-94364) (#94453)

(cherry picked from commit ea39b77de9fa25b447d0b4148f75f351076e890a)

Co-authored-by: neonene <53406459+neonene@users.noreply.github.com>
---
 .../2022-06-29-22-18-36.gh-issue-91719.3APYYI.rst              | 2 ++
 Python/ceval.c                                                 | 3 +++
 2 files changed, 5 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Core and Builtins/2022-06-29-22-18-36.gh-issue-91719.3APYYI.rst

diff --git a/Misc/NEWS.d/next/Core and Builtins/2022-06-29-22-18-36.gh-issue-91719.3APYYI.rst b/Misc/NEWS.d/next/Core and Builtins/2022-06-29-22-18-36.gh-issue-91719.3APYYI.rst
new file mode 100644
index 00000000000000..0d085e88778372
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2022-06-29-22-18-36.gh-issue-91719.3APYYI.rst	
@@ -0,0 +1,2 @@
+Reload ``opcode`` when raising ``unknown opcode error`` in the interpreter main loop,
+for C compilers to generate dispatching code independently.
diff --git a/Python/ceval.c b/Python/ceval.c
index 00fb02718d8a37..b8681617c8c22c 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -5661,6 +5661,9 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
 #else
         EXTRA_CASES  // From opcode.h, a 'case' for each unused opcode
 #endif
+            /* Tell C compilers not to hold the opcode variable in the loop.
+               next_instr points the current instruction without TARGET(). */
+            opcode = _Py_OPCODE(*next_instr);
             fprintf(stderr, "XXX lineno: %d, opcode: %d\n",
                     _PyInterpreterFrame_GetLine(frame),  opcode);
             _PyErr_SetString(tstate, PyExc_SystemError, "unknown opcode");