Specialize LOAD_ATTR with LOAD_ATTR_SLOT and LOAD_ATTR_SPLIT_KEYS

python · markshannon · Jun 10, 2021 · May 26, 2021 · Jun 1, 2021 · Jun 1, 2021
commit 8db0653950309a2b911972acd4f025c0d5e90a78
diff --git a/Include/internal/pycore_code.h b/Include/internal/pycore_code.h
@@ -42,6 +42,12 @@ typedef struct {
     uint16_t index;
 } _PyAdaptiveEntry;
 
+
+typedef struct {
+    uint32_t tp_version;
+    uint32_t dk_version;
+} _PyLoadAttrCache;
+
 /* Add specialized versions of entries to this union.
  *
  * Do not break the invariant: sizeof(SpecializedCacheEntry) == 8
@@ -55,6 +61,7 @@ typedef struct {
 typedef union {
     _PyEntryZero zero;
     _PyAdaptiveEntry adaptive;
+    _PyLoadAttrCache load_attr;
 } SpecializedCacheEntry;
 
 #define INSTRUCTIONS_PER_ENTRY (sizeof(SpecializedCacheEntry)/sizeof(_Py_CODEUNIT))
@@ -255,6 +262,64 @@ PyAPI_FUNC(PyObject *) _PyCode_GetCellvars(PyCodeObject *);
 PyAPI_FUNC(PyObject *) _PyCode_GetFreevars(PyCodeObject *);
 
 
+/* Cache hits and misses */
+
+static inline uint8_t
+saturating_increment(uint8_t c)
+{
+    return c<<1;
+}
+
+static inline uint8_t
+saturating_decrement(uint8_t c)
+{
+    return (c>>1) + 128;
+}
+
+static inline uint8_t
+saturating_zero(void)
+{
+    return 255;
+}
+
+/* Starting value for saturating counter.
+ * Technically this should be 1, but that is likely to
+ * cause a bit of thrashing when we optimize then get an immediate miss.
+ * We want to give the counter a change to stabilize, so we start at 3.
+ */
+static inline uint8_t
+saturating_start(void)
+{
+    return saturating_zero()<<3;
+}
+
+static inline void
+record_cache_hit(_PyAdaptiveEntry *entry) {
+    entry->counter = saturating_increment(entry->counter);
+}
+
+static inline void
+record_cache_miss(_PyAdaptiveEntry *entry) {
+    entry->counter = saturating_decrement(entry->counter);
+}
+
+static inline int
+too_many_cache_misses(_PyAdaptiveEntry *entry) {
+    return entry->counter == saturating_zero();
+}
+
+#define BACKOFF 64
+
+static inline void
+cache_backoff(_PyAdaptiveEntry *entry) {
+    entry->counter = BACKOFF;
+}
+
+/* Specialization functions */
+
+int _Py_Specialize_LoadAttr(PyObject *owner, _Py_CODEUNIT *instr, PyObject *name, SpecializedCacheEntry *cache);
+
+
 #ifdef __cplusplus
 }
 #endif

diff --git a/Include/opcode.h b/Include/opcode.h
diff --git a/Lib/opcode.py b/Lib/opcode.py
@@ -218,3 +218,9 @@ def jabs_op(name, op):
 def_op('CALL_METHOD_KW', 166)
 
 del def_op, name_op, jrel_op, jabs_op
+
+_specialized_instructions = [
+    "LOAD_ATTR_ADAPTIVE",
+    "LOAD_ATTR_SPLIT_KEYS",
+    "LOAD_ATTR_SLOT",
+]