Step 1: replace 'python -Xuops' with 'configure --enable-experimental…

…-tier2'

Doc/whatsnew/3.13.rst

@@ -901,9 +901,8 @@ The internal architecture is roughly as follows.
 
 * There is a Tier 2 interpreter, but it is mostly intended for debugging
   the earlier stages of the optimization pipeline. If the JIT is not
-  enabled, the Tier 2 interpreter can be invoked by passing Python the
-  ``-X uops`` option or by setting the ``PYTHON_UOPS`` environment
-  variable to ``1``.
+  enabled, the Tier 2 interpreter can be enabled by configuring Python
+  with the ``--enable-experimental-tier2`` option.
 
 * When the ``--enable-experimental-jit`` option is used, the optimized
   Tier 2 IR is translated to machine code, which is then executed.

Misc/NEWS.d/next/Core and Builtins/2024-04-26-14-06-18.gh-issue-118335.SRFsxO.rst

@@ -0,0 +1,4 @@
+Change how to use the tier 2 interpreter. Instead of running Python with
+``-X uops`` or setting the environment variable ``PYTHON_UOPS=1``, this
+choice is now made at build time by configuring with
+``--enable-experimental-tier2``.

Python/pylifecycle.c

@@ -1262,30 +1262,19 @@ init_interp_main(PyThreadState *tstate)
     }
 
     // Turn on experimental tier 2 (uops-based) optimizer
+    // This is also needed when the JIT is enabled
+#if defined(_Py_JIT) || defined(_Py_TIER2)
     if (is_main_interp) {
-#ifndef _Py_JIT
-        // No JIT, maybe use the tier two interpreter:
-        char *envvar = Py_GETENV("PYTHON_UOPS");
-        int enabled = envvar != NULL && *envvar > '0';
-        if (_Py_get_xoption(&config->xoptions, L"uops") != NULL) {
-            enabled = 1;
-        }
-        if (enabled) {
-#else
-        // Always enable tier two for JIT builds (ignoring the environment
-        // variable and command-line option above):
-        if (true) {
-#endif
             PyObject *opt = PyUnstable_Optimizer_NewUOpOptimizer();
             if (opt == NULL) {
                 return _PyStatus_ERR("can't initialize optimizer");
             }
             if (PyUnstable_SetOptimizer((_PyOptimizerObject *)opt)) {
-                return _PyStatus_ERR("can't initialize optimizer");
+                return _PyStatus_ERR("can't install optimizer");
             }
             Py_DECREF(opt);
-        }
     }
+#endif
 
     if (!is_main_interp) {
         // The main interpreter is handled in Py_Main(), for now.

configure.ac

@@ -1784,6 +1784,19 @@ AC_SUBST([REGEN_JIT_COMMAND])
 AC_SUBST([JIT_STENCILS_H])
 AC_MSG_RESULT([$enable_experimental_jit])
 
+# Check for --enable-experimental-tier2:
+AC_MSG_CHECKING([for --enable-experimental-tier2])
+AC_ARG_ENABLE([experimental-tier2],
+              [AS_HELP_STRING([--enable-experimental-tier2],
+                              [use the experimental tier 2 interpreter (default is no)])],
+              [],
+              [enable_experimental_tier2=no])
+AS_VAR_IF([enable_experimental_tier2],
+          [no],
+          [],
+          [AS_VAR_APPEND([CFLAGS_NODIST], [" -D_Py_TIER2"])])
+AC_MSG_RESULT([$enable_experimental_tier2])
+
 # Enable optimization flags
 AC_SUBST([DEF_MAKE_ALL_RULE])
 AC_SUBST([DEF_MAKE_RULE])