gh-115859: Re-enable T2 optimizer pass by default (#116062)

This undoes the *temporary* default disabling of the T2 optimizer pass in gh-115860.

- Add a new test that reproduces Brandt's example from gh-115859; it indeed crashes before gh-116028 with PYTHONUOPSOPTIMIZE=1
- Re-enable the optimizer pass in T2, stop checking PYTHONUOPSOPTIMIZE
- Rename the env var to disable T2 entirely to PYTHON_UOPS_OPTIMIZE (must be explicitly set to 0 to disable)
- Fix skipIf conditions on tests in test_opt.py accordingly
- Export sym_is_bottom() (for debugging)
- Fix various things in the `_BINARY_OP_` specializations in the abstract interpreter:
  - DECREF(temp)
  - out-of-space check after sym_new_const()
  - add sym_matches_type() checks, so even if we somehow reach a binary op with symbolic constants of the wrong type on the stack we won't trigger the type assert

Lib/test/test_capi/test_opt.py

@@ -210,6 +210,8 @@ def f():
         exe = get_first_executor(f)
         self.assertIsNone(exe)
 
+
+@unittest.skipIf(os.getenv("PYTHON_UOPS_OPTIMIZE") == "0", "Needs uop optimizer to run.")
 class TestUops(unittest.TestCase):
 
     def test_basic_loop(self):
@@ -570,7 +572,7 @@ def testfunc(n):
         self.assertLessEqual(count, 2)
 
 
-@unittest.skipIf(os.getenv("PYTHONUOPSOPTIMIZE", default=0) == 0, "Needs uop optimizer to run.")
+@unittest.skipIf(os.getenv("PYTHON_UOPS_OPTIMIZE") == "0", "Needs uop optimizer to run.")
 class TestUopsOptimization(unittest.TestCase):
 
     def _run_with_optimizer(self, testfunc, arg):
@@ -890,5 +892,22 @@ def testfunc(n):
         self.assertLessEqual(len(guard_both_float_count), 1)
         self.assertIn("_COMPARE_OP_STR", uops)
 
+    def test_type_inconsistency(self):
+        def testfunc(n):
+            for i in range(n):
+                x = _test_global + _test_global
+        # Must be a real global else it won't be optimized to _LOAD_CONST_INLINE
+        global _test_global
+        _test_global = 0
+        _, ex = self._run_with_optimizer(testfunc, 16)
+        self.assertIsNone(ex)
+        _test_global = 1.2
+        _, ex = self._run_with_optimizer(testfunc, 16)
+        self.assertIsNotNone(ex)
+        uops = get_opnames(ex)
+        self.assertIn("_GUARD_BOTH_INT", uops)
+        self.assertIn("_BINARY_OP_ADD_INT", uops)
+
+
 if __name__ == "__main__":
     unittest.main()