Reduce costs of checking if lazy imports are enabled

Summary: Checking if lazy imports is showing up as a significant (2%) cost in some workloads.  Those workloads are probably already less than ideal in that they're presumably doing imports in functions which is a bad idea.  But we can make that better by first checking to see if we're at a global scope which is super cheap.

Reviewed By: itamaro, Kronuz, cxxxs

Differential Revision: D49522414

fbshipit-source-id: 4ca46456309b36f4f75d03f493eaaf44068548e6

Python/ceval.c

@@ -3711,9 +3711,9 @@ f->lazy_imports_cache_seq = -1;
             PyObject *level = TOP();
             PyObject *res;
 
-            if (_PyImport_IsLazyImportsEnabled(tstate)
-                && f->f_globals == f->f_locals
-                && f->f_iblock == 0) {
+            if (f->f_globals == f->f_locals &&
+                f->f_iblock == 0 &&
+                _PyImport_IsLazyImportsEnabled(tstate)) {
                 res = _PyImport_LazyImportName(f->f_builtins,
                                                f->f_globals,
                                                f->f_locals == NULL ? Py_None : f->f_locals,