gh-119258: Eliminate Type Guards in Tier 2 Optimizer with Watcher (GH-119365)

Co-authored-by: parmeggiani <parmeggiani@spaziodati.eu>
Co-authored-by: dpdani <git@danieleparmeggiani.me>
Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: Brandt Bucher <brandtbucher@microsoft.com>
Co-authored-by: Ken Jin <kenjin@python.org>

Python/optimizer_analysis.c

@@ -79,6 +79,7 @@ increment_mutations(PyObject* dict) {
  * so we don't need to check that they haven't been used */
 #define BUILTINS_WATCHER_ID 0
 #define GLOBALS_WATCHER_ID  1
+#define TYPE_WATCHER_ID  0
 
 static int
 globals_watcher_callback(PyDict_WatchEvent event, PyObject* dict,
@@ -92,6 +93,14 @@ globals_watcher_callback(PyDict_WatchEvent event, PyObject* dict,
     return 0;
 }
 
+static int
+type_watcher_callback(PyTypeObject* type)
+{
+    _Py_Executors_InvalidateDependency(_PyInterpreterState_GET(), type, 1);
+    PyType_Unwatch(TYPE_WATCHER_ID, (PyObject *)type);
+    return 0;
+}
+
 static PyObject *
 convert_global_to_const(_PyUOpInstruction *inst, PyObject *obj)
 {
@@ -167,6 +176,9 @@ remove_globals(_PyInterpreterFrame *frame, _PyUOpInstruction *buffer,
     if (interp->dict_state.watchers[GLOBALS_WATCHER_ID] == NULL) {
         interp->dict_state.watchers[GLOBALS_WATCHER_ID] = globals_watcher_callback;
     }
+    if (interp->type_watchers[TYPE_WATCHER_ID] == NULL) {
+        interp->type_watchers[TYPE_WATCHER_ID] = type_watcher_callback;
+    }
     for (int pc = 0; pc < buffer_size; pc++) {
         _PyUOpInstruction *inst = &buffer[pc];
         int opcode = inst->opcode;
@@ -310,9 +322,11 @@ remove_globals(_PyInterpreterFrame *frame, _PyUOpInstruction *buffer,
 #define sym_has_type _Py_uop_sym_has_type
 #define sym_get_type _Py_uop_sym_get_type
 #define sym_matches_type _Py_uop_sym_matches_type
+#define sym_matches_type_version _Py_uop_sym_matches_type_version
 #define sym_set_null(SYM) _Py_uop_sym_set_null(ctx, SYM)
 #define sym_set_non_null(SYM) _Py_uop_sym_set_non_null(ctx, SYM)
 #define sym_set_type(SYM, TYPE) _Py_uop_sym_set_type(ctx, SYM, TYPE)
+#define sym_set_type_version(SYM, VERSION) _Py_uop_sym_set_type_version(ctx, SYM, VERSION)
 #define sym_set_const(SYM, CNST) _Py_uop_sym_set_const(ctx, SYM, CNST)
 #define sym_is_bottom _Py_uop_sym_is_bottom
 #define sym_truthiness _Py_uop_sym_truthiness
@@ -395,7 +409,7 @@ optimize_uops(
     _PyUOpInstruction *corresponding_check_stack = NULL;
 
     _Py_uop_abstractcontext_init(ctx);
-    _Py_UOpsAbstractFrame *frame = _Py_uop_frame_new(ctx, co, ctx->n_consumed, 0, curr_stacklen);
+    _Py_UOpsAbstractFrame *frame = _Py_uop_frame_new(ctx, co, curr_stacklen, NULL, 0);
     if (frame == NULL) {
         return -1;
     }

Python/optimizer_bytecodes.c

@@ -21,11 +21,13 @@ typedef struct _Py_UOpsAbstractFrame _Py_UOpsAbstractFrame;
 #define sym_new_const _Py_uop_sym_new_const
 #define sym_new_null _Py_uop_sym_new_null
 #define sym_matches_type _Py_uop_sym_matches_type
+#define sym_matches_type_version _Py_uop_sym_matches_type_version
 #define sym_get_type _Py_uop_sym_get_type
 #define sym_has_type _Py_uop_sym_has_type
 #define sym_set_null(SYM) _Py_uop_sym_set_null(ctx, SYM)
 #define sym_set_non_null(SYM) _Py_uop_sym_set_non_null(ctx, SYM)
 #define sym_set_type(SYM, TYPE) _Py_uop_sym_set_type(ctx, SYM, TYPE)
+#define sym_set_type_version(SYM, VERSION) _Py_uop_sym_set_type_version(ctx, SYM, VERSION)
 #define sym_set_const(SYM, CNST) _Py_uop_sym_set_const(ctx, SYM, CNST)
 #define sym_is_bottom _Py_uop_sym_is_bottom
 #define frame_new _Py_uop_frame_new
@@ -113,6 +115,29 @@ dummy_func(void) {
         sym_set_type(right, &PyLong_Type);
     }
 
+    op(_GUARD_TYPE_VERSION, (type_version/2, owner -- owner)) {
+        assert(type_version);
+        if (sym_matches_type_version(owner, type_version)) {
+            REPLACE_OP(this_instr, _NOP, 0, 0);
+        } else {
+            // add watcher so that whenever the type changes we invalidate this
+            PyTypeObject *type = _PyType_LookupByVersion(type_version);
+            // if the type is null, it was not found in the cache (there was a conflict)
+            // with the key, in which case we can't trust the version
+            if (type) {
+                // if the type version was set properly, then add a watcher
+                // if it wasn't this means that the type version was previously set to something else
+                // and we set the owner to bottom, so we don't need to add a watcher because we must have
+                // already added one earlier.
+                if (sym_set_type_version(owner, type_version)) {
+                    PyType_Watch(TYPE_WATCHER_ID, (PyObject *)type);
+                    _Py_BloomFilter_Add(dependencies, type);
+                }
+            }
+
+        }
+    }
+
     op(_GUARD_BOTH_FLOAT, (left, right -- left, right)) {
         if (sym_matches_type(left, &PyFloat_Type)) {
             if (sym_matches_type(right, &PyFloat_Type)) {
@@ -563,16 +588,12 @@ dummy_func(void) {
             argcount++;
         }
 
-        _Py_UopsSymbol **localsplus_start = ctx->n_consumed;
-        int n_locals_already_filled = 0;
-        // Can determine statically, so we interleave the new locals
-        // and make the current stack the new locals.
-        // This also sets up for true call inlining.
         if (sym_is_null(self_or_null) || sym_is_not_null(self_or_null)) {
-            localsplus_start = args;
-            n_locals_already_filled = argcount;
+            new_frame = frame_new(ctx, co, 0, args, argcount);
+        } else {
+            new_frame = frame_new(ctx, co, 0, NULL, 0);
+
         }
-        new_frame = frame_new(ctx, co, localsplus_start, n_locals_already_filled, 0);
     }
 
     op(_PY_FRAME_GENERAL, (callable, self_or_null, args[oparg] -- new_frame: _Py_UOpsAbstractFrame *)) {

Python/optimizer_cases.c.h

@@ -930,6 +930,28 @@
         }
 
         case _GUARD_TYPE_VERSION: {
+            _Py_UopsSymbol *owner;
+            owner = stack_pointer[-1];
+            uint32_t type_version = (uint32_t)this_instr->operand;
+            assert(type_version);
+            if (sym_matches_type_version(owner, type_version)) {
+                REPLACE_OP(this_instr, _NOP, 0, 0);
+            } else {
+                // add watcher so that whenever the type changes we invalidate this
+                PyTypeObject *type = _PyType_LookupByVersion(type_version);
+                // if the type is null, it was not found in the cache (there was a conflict)
+                // with the key, in which case we can't trust the version
+                if (type) {
+                    // if the type version was set properly, then add a watcher
+                    // if it wasn't this means that the type version was previously set to something else
+                    // and we set the owner to bottom, so we don't need to add a watcher because we must have
+                    // already added one earlier.
+                    if (sym_set_type_version(owner, type_version)) {
+                        PyType_Watch(TYPE_WATCHER_ID, (PyObject *)type);
+                        _Py_BloomFilter_Add(dependencies, type);
+                    }
+                }
+            }
             break;
         }
 
@@ -1583,16 +1605,11 @@
                 args--;
                 argcount++;
             }
-            _Py_UopsSymbol **localsplus_start = ctx->n_consumed;
-            int n_locals_already_filled = 0;
-            // Can determine statically, so we interleave the new locals
-            // and make the current stack the new locals.
-            // This also sets up for true call inlining.
             if (sym_is_null(self_or_null) || sym_is_not_null(self_or_null)) {
-                localsplus_start = args;
-                n_locals_already_filled = argcount;
+                new_frame = frame_new(ctx, co, 0, args, argcount);
+            } else {
+                new_frame = frame_new(ctx, co, 0, NULL, 0);
             }
-            new_frame = frame_new(ctx, co, localsplus_start, n_locals_already_filled, 0);
             stack_pointer[-2 - oparg] = (_Py_UopsSymbol *)new_frame;
             stack_pointer += -1 - oparg;
             break;

Python/optimizer_symbols.c

@@ -52,7 +52,8 @@ static inline int get_lltrace(void) {
 static _Py_UopsSymbol NO_SPACE_SYMBOL = {
     .flags = IS_NULL | NOT_NULL | NO_SPACE,
     .typ = NULL,
-    .const_val = NULL
+    .const_val = NULL,
+    .type_version = 0,
 };
 
 _Py_UopsSymbol *
@@ -76,6 +77,7 @@ sym_new(_Py_UOpsContext *ctx)
     self->flags = 0;
     self->typ = NULL;
     self->const_val = NULL;
+    self->type_version = 0;
 
     return self;
 }
@@ -152,6 +154,18 @@ _Py_uop_sym_set_type(_Py_UOpsContext *ctx, _Py_UopsSymbol *sym, PyTypeObject *ty
     }
 }
 
+bool
+_Py_uop_sym_set_type_version(_Py_UOpsContext *ctx, _Py_UopsSymbol *sym, unsigned int version)
+{
+    // if the type version was already set, then it must be different and we should set it to bottom
+    if (sym->type_version) {
+        sym_set_bottom(ctx, sym);
+        return false;
+    }
+    sym->type_version = version;
+    return true;
+}
+
 void
 _Py_uop_sym_set_const(_Py_UOpsContext *ctx, _Py_UopsSymbol *sym, PyObject *const_val)
 {
@@ -256,6 +270,12 @@ _Py_uop_sym_get_type(_Py_UopsSymbol *sym)
     return sym->typ;
 }
 
+unsigned int
+_Py_uop_sym_get_type_version(_Py_UopsSymbol *sym)
+{
+    return sym->type_version;
+}
+
 bool
 _Py_uop_sym_has_type(_Py_UopsSymbol *sym)
 {
@@ -272,6 +292,13 @@ _Py_uop_sym_matches_type(_Py_UopsSymbol *sym, PyTypeObject *typ)
     return _Py_uop_sym_get_type(sym) == typ;
 }
 
+bool
+_Py_uop_sym_matches_type_version(_Py_UopsSymbol *sym, unsigned int version)
+{
+    return _Py_uop_sym_get_type_version(sym) == version;
+}
+
+
 int
 _Py_uop_sym_truthiness(_Py_UopsSymbol *sym)
 {
@@ -311,9 +338,9 @@ _Py_UOpsAbstractFrame *
 _Py_uop_frame_new(
     _Py_UOpsContext *ctx,
     PyCodeObject *co,
-    _Py_UopsSymbol **localsplus_start,
-    int n_locals_already_filled,
-    int curr_stackentries)
+    int curr_stackentries,
+    _Py_UopsSymbol **args,
+    int arg_len)
 {
     assert(ctx->curr_frame_depth < MAX_ABSTRACT_FRAME_DEPTH);
     _Py_UOpsAbstractFrame *frame = &ctx->frames[ctx->curr_frame_depth];
@@ -321,19 +348,22 @@ _Py_uop_frame_new(
     frame->stack_len = co->co_stacksize;
     frame->locals_len = co->co_nlocalsplus;
 
-    frame->locals = localsplus_start;
+    frame->locals = ctx->n_consumed;
     frame->stack = frame->locals + co->co_nlocalsplus;
     frame->stack_pointer = frame->stack + curr_stackentries;
-    ctx->n_consumed = localsplus_start + (co->co_nlocalsplus + co->co_stacksize);
+    ctx->n_consumed = ctx->n_consumed + (co->co_nlocalsplus + co->co_stacksize);
     if (ctx->n_consumed >= ctx->limit) {
         ctx->done = true;
         ctx->out_of_space = true;
         return NULL;
     }
 
-
     // Initialize with the initial state of all local variables
-    for (int i = n_locals_already_filled; i < co->co_nlocalsplus; i++) {
+    for (int i = 0; i < arg_len; i++) {
+        frame->locals[i] = args[i];
+    }
+
+    for (int i = arg_len; i < co->co_nlocalsplus; i++) {
         _Py_UopsSymbol *local = _Py_uop_sym_new_unknown(ctx);
         frame->locals[i] = local;
     }