gh-104584: Baby steps towards generating and executing traces (#105924)

Added a new, experimental, tracing optimizer and interpreter (a.k.a. "tier 2"). This currently pessimizes, so don't use yet -- this is infrastructure so we can experiment with optimizing passes. To enable it, pass ``-Xuops`` or set ``PYTHONUOPS=1``. To get debug output, set ``PYTHONUOPSDEBUG=N`` where ``N`` is a debug level (0-4, where 0 is no debug output and 4 is excessively verbose).

All of this code is likely to change dramatically before the 3.13 feature freeze. But this is a first step.

1 files changed, 13 insertions, 0 deletions

diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index 5a5b14fbb03..6117f3a19a5 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -1181,6 +1181,19 @@ init_interp_main(PyThreadState *tstate)
 #endif
     }
 
+    // Turn on experimental tier 2 (uops-based) optimizer
+    if (is_main_interp) {
+        char *envvar = Py_GETENV("PYTHONUOPS");
+        int enabled = envvar != NULL && *envvar > '0';
+        if (_Py_get_xoption(&config->xoptions, L"uops") != NULL) {
+            enabled = 1;
+        }
+        if (enabled) {
+            PyObject *opt = PyUnstable_Optimizer_NewUOpOptimizer();
+            PyUnstable_SetOptimizer((_PyOptimizerObject *)opt);
+        }
+    }
+
     assert(!_PyErr_Occurred(tstate));
 
     return _PyStatus_OK();