Add slots object property tracking for the Tier 2 JIT optimizer

Fidget-Spinner · Jan 30, 2026 · Jan 20, 2026 · Jan 21, 2026 · Jan 21, 2026 · Jan 22, 2026
commit dfd99d78ebd4991e10f4e326ac63aef12aced7d5
diff --git a/Include/internal/pycore_optimizer.h b/Include/internal/pycore_optimizer.h
@@ -205,6 +205,9 @@ extern JitOptRef _Py_uop_sym_new_truthiness(JitOptContext *ctx, JitOptRef value,
 extern bool _Py_uop_sym_is_compact_int(JitOptRef sym);
 extern JitOptRef _Py_uop_sym_new_compact_int(JitOptContext *ctx);
 extern void _Py_uop_sym_set_compact_int(JitOptContext *ctx,  JitOptRef sym);
+extern JitOptRef _Py_uop_sym_new_slots_object(JitOptContext *ctx, unsigned int type_version);
+extern JitOptRef _Py_uop_sym_slots_getattr(JitOptContext *ctx, JitOptRef ref, uint16_t slot_index);
+extern void _Py_uop_sym_slots_setattr(JitOptContext *ctx, JitOptRef ref, uint16_t slot_index, JitOptRef value);
 
 extern void _Py_uop_abstractcontext_init(JitOptContext *ctx);
 extern void _Py_uop_abstractcontext_fini(JitOptContext *ctx);

diff --git a/Include/internal/pycore_optimizer_types.h b/Include/internal/pycore_optimizer_types.h
@@ -40,6 +40,7 @@ typedef enum _JitSymType {
     JIT_SYM_TUPLE_TAG = 8,
     JIT_SYM_TRUTHINESS_TAG = 9,
     JIT_SYM_COMPACT_INT = 10,
+    JIT_SYM_SLOTS_TAG = 11,
 } JitSymType;
 
 typedef struct _jit_opt_known_class {
@@ -76,6 +77,20 @@ typedef struct {
     uint8_t tag;
 } JitOptCompactInt;
 
+#define MAX_SYMBOLIC_SLOTS_SIZE 4
+
+typedef struct {
+    uint16_t slot_index;
+    uint16_t symbol;
+} JitOptSlotMapping;
+
+typedef struct _jit_opt_slots {
+    uint8_t tag;
+    uint8_t num_slots;
+    uint32_t type_version;
+    JitOptSlotMapping slots[MAX_SYMBOLIC_SLOTS_SIZE];
+} JitOptSlotsObject;
+
 typedef union _jit_opt_symbol {
     uint8_t tag;
     JitOptKnownClass cls;
@@ -84,6 +99,7 @@ typedef union _jit_opt_symbol {
     JitOptTuple tuple;
     JitOptTruthiness truthiness;
     JitOptCompactInt compact;
+    JitOptSlotsObject slots;
 } JitOptSymbol;
 
 // This mimics the _PyStackRef API

@@ -247,6 +247,9 @@ add_op(JitOptContext *ctx, _PyUOpInstruction *this_instr,
 #define sym_is_compact_int _Py_uop_sym_is_compact_int
 #define sym_new_compact_int _Py_uop_sym_new_compact_int
 #define sym_new_truthiness _Py_uop_sym_new_truthiness
+#define sym_new_slots_object _Py_uop_sym_new_slots_object
+#define sym_slots_getattr _Py_uop_sym_slots_getattr
+#define sym_slots_setattr _Py_uop_sym_slots_setattr
 
 #define JUMP_TO_LABEL(label) goto label;
 

@@ -38,6 +38,9 @@ typedef struct _Py_UOpsAbstractFrame _Py_UOpsAbstractFrame;
 #define sym_new_compact_int _Py_uop_sym_new_compact_int
 #define sym_is_compact_int _Py_uop_sym_is_compact_int
 #define sym_new_truthiness _Py_uop_sym_new_truthiness
+#define sym_new_slots_object _Py_uop_sym_new_slots_object
+#define sym_slots_getattr _Py_uop_sym_slots_getattr
+#define sym_slots_setattr _Py_uop_sym_slots_setattr
 
 extern int
 optimize_to_bool(
@@ -123,8 +126,7 @@ dummy_func(void) {
     }
 
     op(_STORE_ATTR_SLOT, (index/1, value, owner -- o)) {
-        (void)index;
-        (void)value;
+        sym_slots_setattr(ctx, owner, (uint16_t)index, value);
         o = owner;
     }
 
@@ -709,8 +711,7 @@ dummy_func(void) {
     }
 
     op(_LOAD_ATTR_SLOT, (index/1, owner -- attr, o)) {
-        attr = sym_new_not_null(ctx);
-        (void)index;
+        attr = sym_slots_getattr(ctx, owner, (uint16_t)index);
         o = owner;
     }
 

diff --git a/Python/optimizer_cases.c.h b/Python/optimizer_cases.c.h
@@ -113,6 +113,9 @@ _PyUOpSymPrint(JitOptRef ref)
         case JIT_SYM_COMPACT_INT:
             printf("<compact_int at %p>", (void *)sym);
             break;
+        case JIT_SYM_SLOTS_TAG:
+            printf("<slots[%d] v%u at %p>", sym->slots.num_slots, sym->slots.type_version, (void *)sym);
+            break;
         default:
             printf("<tag=%d at %p>", sym->tag, (void *)sym);
             break;
@@ -319,6 +322,11 @@ _Py_uop_sym_set_type(JitOptContext *ctx, JitOptRef ref, PyTypeObject *typ)
                 sym_set_bottom(ctx, sym);
             }
             return;
+        case JIT_SYM_SLOTS_TAG:
+            if (typ->tp_version_tag != sym->slots.type_version) {
+                sym_set_bottom(ctx, sym);
+            }
+            return;
     }
 }
 
@@ -382,6 +390,12 @@ _Py_uop_sym_set_type_version(JitOptContext *ctx, JitOptRef ref, unsigned int ver
                 return false;
             }
             return true;
+        case JIT_SYM_SLOTS_TAG:
+            if (version != sym->slots.type_version) {
+                sym_set_bottom(ctx, sym);
+                return false;
+            }
+            return true;
     }
     Py_UNREACHABLE();
 }
@@ -474,6 +488,9 @@ _Py_uop_sym_set_const(JitOptContext *ctx, JitOptRef ref, PyObject *const_val)
                 sym_set_bottom(ctx, sym);
             }
             return;
+        case JIT_SYM_SLOTS_TAG:
+            sym_set_bottom(ctx, sym);
+            return;
     }
 }
 
@@ -593,7 +610,8 @@ _Py_uop_sym_get_type(JitOptRef ref)
             return &PyBool_Type;
         case JIT_SYM_COMPACT_INT:
             return &PyLong_Type;
-
+        case JIT_SYM_SLOTS_TAG:
+            return _PyType_LookupByVersion(sym->slots.type_version);
     }
     Py_UNREACHABLE();
 }
@@ -621,6 +639,8 @@ _Py_uop_sym_get_type_version(JitOptRef ref)
             return PyBool_Type.tp_version_tag;
         case JIT_SYM_COMPACT_INT:
             return PyLong_Type.tp_version_tag;
+        case JIT_SYM_SLOTS_TAG:
+            return sym->slots.type_version;
     }
     Py_UNREACHABLE();
 }
@@ -655,6 +675,7 @@ _Py_uop_sym_truthiness(JitOptContext *ctx, JitOptRef ref)
         case JIT_SYM_NON_NULL_TAG:
         case JIT_SYM_UNKNOWN_TAG:
         case JIT_SYM_COMPACT_INT:
+        case JIT_SYM_SLOTS_TAG:
             return -1;
         case JIT_SYM_KNOWN_CLASS_TAG:
             /* TODO :
@@ -811,6 +832,7 @@ _Py_uop_sym_set_compact_int(JitOptContext *ctx, JitOptRef ref)
             return;
         case JIT_SYM_TUPLE_TAG:
         case JIT_SYM_TRUTHINESS_TAG:
+        case JIT_SYM_SLOTS_TAG:
             sym_set_bottom(ctx, sym);
             return;
         case JIT_SYM_BOTTOM_TAG:
@@ -859,6 +881,74 @@ _Py_uop_sym_new_compact_int(JitOptContext *ctx)
     return PyJitRef_Wrap(sym);
 }
 
+JitOptRef
+_Py_uop_sym_new_slots_object(JitOptContext *ctx, unsigned int type_version)
+{
+    JitOptSymbol *res = sym_new(ctx);
+    if (res == NULL) {
+        return out_of_space_ref(ctx);
+    }
+    res->tag = JIT_SYM_SLOTS_TAG;
+    res->slots.num_slots = 0;
+    res->slots.type_version = type_version;
+    return PyJitRef_Wrap(res);
+}
+
+JitOptRef
+_Py_uop_sym_slots_getattr(JitOptContext *ctx, JitOptRef ref, uint16_t slot_index)
+{
+    JitOptSymbol *sym = PyJitRef_Unwrap(ref);
+
+    if (sym->tag == JIT_SYM_SLOTS_TAG) {
+        // Linear search through the mapping array
+        for (int i = 0; i < sym->slots.num_slots; i++) {
+            if (sym->slots.slots[i].slot_index == slot_index) {
+                return PyJitRef_Wrap(allocation_base(ctx) + sym->slots.slots[i].symbol);
+            }
+        }
+    }
+
+    // Not found, return not_null
+    return _Py_uop_sym_new_not_null(ctx);
+}
+
+void
+_Py_uop_sym_slots_setattr(JitOptContext *ctx, JitOptRef ref, uint16_t slot_index, JitOptRef value)
+{
+    JitOptSymbol *sym = PyJitRef_Unwrap(ref);
+
+    if (sym->tag == JIT_SYM_TYPE_VERSION_TAG) {
+        uint32_t version = sym->version.version;
+        sym->tag = JIT_SYM_SLOTS_TAG;
+        sym->slots.type_version = version;
+        sym->slots.num_slots = 0;
+    }
+    else if (sym->tag == JIT_SYM_KNOWN_CLASS_TAG) {
+        uint32_t version = sym->cls.version;
+        sym->tag = JIT_SYM_SLOTS_TAG;
+        sym->slots.type_version = version;
+        sym->slots.num_slots = 0;
+    }
+    else if (sym->tag != JIT_SYM_SLOTS_TAG) {
+        return;
+    }
+
+    if (sym->slots.num_slots >= MAX_SYMBOLIC_SLOTS_SIZE) {
+        return;
+    }
+
+    for (int i = 0; i < sym->slots.num_slots; i++) {
+        if (sym->slots.slots[i].slot_index == slot_index) {
+            sym->slots.slots[i].symbol = (uint16_t)(PyJitRef_Unwrap(value) - allocation_base(ctx));
+            return;
+        }
+    }
+
+    int idx = sym->slots.num_slots++;
+    sym->slots.slots[idx].slot_index = slot_index;
+    sym->slots.slots[idx].symbol = (uint16_t)(PyJitRef_Unwrap(value) - allocation_base(ctx));
+}
+
 // 0 on success, -1 on error.
 _Py_UOpsAbstractFrame *
 _Py_uop_frame_new(
@@ -1186,6 +1276,33 @@ _Py_uop_symbols_test(PyObject *Py_UNUSED(self), PyObject *Py_UNUSED(ignored))
     TEST_PREDICATE(_Py_uop_sym_matches_type(ref_int, &PyLong_Type), "43 is not an int");
     TEST_PREDICATE(_Py_uop_sym_get_const(ctx, ref_int) == val_43, "43 isn't 43");
 
+    JitOptRef slots_obj = _Py_uop_sym_new_slots_object(ctx, 42);
+    TEST_PREDICATE(!_Py_uop_sym_is_null(slots_obj), "slots object is NULL");
+    TEST_PREDICATE(_Py_uop_sym_is_not_null(slots_obj), "slots object is not not-null");
+    TEST_PREDICATE(_Py_uop_sym_get_type_version(slots_obj) == 42,
+                   "slots object has wrong type version");
+
+    JitOptRef slot_val = _Py_uop_sym_new_const(ctx, val_42);
+    _Py_uop_sym_slots_setattr(ctx, slots_obj, 0, slot_val);
+    JitOptRef retrieved = _Py_uop_sym_slots_getattr(ctx, slots_obj, 0);
+    TEST_PREDICATE(_Py_uop_sym_get_const(ctx, retrieved) == val_42,
+                   "slots getattr(0) didn't return val_42");
+
+    JitOptRef missing = _Py_uop_sym_slots_getattr(ctx, slots_obj, 99);
+    TEST_PREDICATE(_Py_uop_sym_is_not_null(missing), "missing slot is not not-null");
+    TEST_PREDICATE(!_Py_uop_sym_is_const(ctx, missing), "missing slot is const");
+
+    JitOptRef slot_val2 = _Py_uop_sym_new_const(ctx, val_43);
+    _Py_uop_sym_slots_setattr(ctx, slots_obj, 0, slot_val2);
+    retrieved = _Py_uop_sym_slots_getattr(ctx, slots_obj, 0);
+    TEST_PREDICATE(_Py_uop_sym_get_const(ctx, retrieved) == val_43,
+                   "slots getattr(0) didn't return val_43 after update");
+
+    JitOptRef slots_obj2 = _Py_uop_sym_new_slots_object(ctx, 42);
+    _Py_uop_sym_set_type_version(ctx, slots_obj2, 43);
+    TEST_PREDICATE(_Py_uop_sym_is_bottom(slots_obj2),
+                   "slots object with wrong type version isn't bottom");
+
     _Py_uop_abstractcontext_fini(ctx);
     Py_DECREF(val_42);
     Py_DECREF(val_43);