infra: LoadAttr specialization bridges

SonicField · SonicField · commit 8382896c8541 · 2026-04-21T15:11:36.000-07:00
2 new bridges for emitLoadAttr specialized opcode paths:
- hir_builder_get_attr_cache: read _PyAttrCache version/index
  from CPython inline cache at bytecode instruction offset
- hir_find_type_by_version_tag: tree walk from PyBaseObject_Type
  to find PyTypeObject by tp_version_tag

These unlock LOAD_ATTR_MODULE, LOAD_ATTR_SLOT, LOAD_ATTR_INSTANCE_VALUE
conversion in emitLoadAttr.
diff --git a/Python/jit/hir/hir_c_api.cpp b/Python/jit/hir/hir_c_api.cpp
@@ -2650,4 +2650,39 @@ void *hir_builder_preloader_preloaded_type(void *builder, PyObject *descr,
   return pt.type.get();
 }
 
+void hir_builder_get_attr_cache(void *builder, int instr_idx,
+                                 uint32_t *version_out, uint16_t *index_out) {
+  auto *b = static_cast<jit::hir::HIRBuilder*>(builder);
+  PyCodeObject *code = b->preloader().code();
+  _Py_CODEUNIT *code_units = (_Py_CODEUNIT *)code->co_code_adaptive;
+  const _PyAttrCache *cache =
+      reinterpret_cast<const _PyAttrCache *>(&code_units[instr_idx + 1]);
+  *version_out = cache->version[0] | (static_cast<uint32_t>(cache->version[1]) << 16);
+  *index_out = cache->index;
+}
+
+static PyTypeObject *findTypeByVersionTagWalk(PyTypeObject *type, uint32_t version) {
+  if (type->tp_version_tag == version) {
+    return type;
+  }
+  PyObject *subclasses = (PyObject *)type->tp_subclasses;
+  if (subclasses == nullptr) {
+    return nullptr;
+  }
+  Py_ssize_t pos = 0;
+  PyObject *ref;
+  while (PyDict_Next(subclasses, &pos, nullptr, &ref)) {
+    PyObject *subtype_obj = PyWeakref_GET_OBJECT(ref);
+    if (subtype_obj == Py_None) continue;
+    PyTypeObject *subtype = (PyTypeObject *)subtype_obj;
+    PyTypeObject *found = findTypeByVersionTagWalk(subtype, version);
+    if (found) return found;
+  }
+  return nullptr;
+}
+
+PyTypeObject *hir_find_type_by_version_tag(uint32_t version) {
+  return findTypeByVersionTagWalk(&PyBaseObject_Type, version);
+}
+
 } /* extern "C" */
diff --git a/Python/jit/hir/hir_c_api.h b/Python/jit/hir/hir_c_api.h
@@ -784,6 +784,14 @@ void hir_instr_expand_into(void *original, void **expansion, size_t count);
 /* Get the BasicBlock* for a given bytecode offset from the builder's block map. */
 void *hir_builder_get_block_at_off(void *builder, int byte_offset);
 
+/* Read _PyAttrCache inline cache from bytecode at instr_idx.
+ * Returns version (uint32) and index (uint16). */
+void hir_builder_get_attr_cache(void *builder, int instr_idx,
+                                 uint32_t *version_out, uint16_t *index_out);
+
+/* Find a PyTypeObject by its tp_version_tag. Returns NULL if not found. */
+PyTypeObject *hir_find_type_by_version_tag(uint32_t version);
+
 /* ---- Preloader bridges (Tier 4 emit conversion) ---- */
 
 /* Get the Preloader's annotations (HirAnnotationIndex*). */
