gh-115816: Improve internal symbols API in optimizer (#116028)

- Any `sym_set_...` call that attempts to set conflicting information
  cause the symbol to become `bottom` (contradiction).
- All `sym_is...` and similar calls return false or NULL for `bottom`.
- Everything's tested.
- The tests still pass with `PYTHONUOPSOPTIMIZE=1`.

Author: gvanrossum

Include/internal/pycore_optimizer.h

@@ -27,12 +27,12 @@ extern PyTypeObject _PyUOpExecutor_Type;
 extern PyTypeObject _PyUOpOptimizer_Type;
 
 /* Symbols */
+/* See explanation in optimizer_symbols.c */
 
 struct _Py_UopsSymbol {
-    int flags;
-    PyTypeObject *typ;
-    // constant propagated value (might be NULL)
-    PyObject *const_val;
+    int flags;  // 0 bits: Top; 2 or more bits: Bottom
+    PyTypeObject *typ;  // Borrowed reference
+    PyObject *const_val;  // Owned reference (!)
 };
 
 // Holds locals, stack, locals, stack ... co_consts (in that order)
@@ -92,7 +92,9 @@ extern _Py_UopsSymbol *_Py_uop_sym_new_const(_Py_UOpsContext *ctx, PyObject *con
 extern _Py_UopsSymbol *_Py_uop_sym_new_null(_Py_UOpsContext *ctx);
 extern bool _Py_uop_sym_matches_type(_Py_UopsSymbol *sym, PyTypeObject *typ);
 extern void _Py_uop_sym_set_null(_Py_UopsSymbol *sym);
-extern void _Py_uop_sym_set_type(_Py_UopsSymbol *sym, PyTypeObject *tp);
+extern void _Py_uop_sym_set_non_null(_Py_UopsSymbol *sym);
+extern void _Py_uop_sym_set_type(_Py_UopsSymbol *sym, PyTypeObject *typ);
+extern void _Py_uop_sym_set_const(_Py_UopsSymbol *sym, PyObject *const_val);
 
 extern int _Py_uop_abstractcontext_init(_Py_UOpsContext *ctx);
 extern void _Py_uop_abstractcontext_fini(_Py_UOpsContext *ctx);

Python/optimizer_analysis.c

@@ -294,7 +294,9 @@ remove_globals(_PyInterpreterFrame *frame, _PyUOpInstruction *buffer,
 #define sym_new_null _Py_uop_sym_new_null
 #define sym_matches_type _Py_uop_sym_matches_type
 #define sym_set_null _Py_uop_sym_set_null
+#define sym_set_non_null _Py_uop_sym_set_non_null
 #define sym_set_type _Py_uop_sym_set_type
+#define sym_set_const _Py_uop_sym_set_const
 #define frame_new _Py_uop_frame_new
 #define frame_pop _Py_uop_frame_pop
 

Python/optimizer_bytecodes.c

@@ -22,7 +22,9 @@ typedef struct _Py_UOpsAbstractFrame _Py_UOpsAbstractFrame;
 #define sym_new_null _Py_uop_sym_new_null
 #define sym_matches_type _Py_uop_sym_matches_type
 #define sym_set_null _Py_uop_sym_set_null
+#define sym_set_non_null _Py_uop_sym_set_non_null
 #define sym_set_type _Py_uop_sym_set_type
+#define sym_set_const _Py_uop_sym_set_const
 #define frame_new _Py_uop_frame_new
 #define frame_pop _Py_uop_frame_pop