gh-134584: Eliminate redundant refcounting from _LOAD_ATTR_SLOT

Signed-off-by: Manjusaka <me@manjusaka.me>

Author: Zheaoli

Include/internal/pycore_opcode_metadata.h

@@ -2573,6 +2573,25 @@ class C:
         self.assertNotIn("_POP_TOP", uops)
         self.assertIn("_POP_TOP_NOP", uops)
 
+    def test_load_addr_slot(self):
+        def testfunc(n):
+            class C:
+                __slots__ = ('x',)
+            c = C()
+            c.x = 42
+            x = 0
+            for _ in range(n):
+                x += c.x
+            return x
+        res, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
+        self.assertEqual(res, 42 * TIER2_THRESHOLD)
+        self.assertIsNotNone(ex)
+        uops = get_opnames(ex)
+
+        self.assertIn("_LOAD_ATTR_SLOT", uops)
+        self.assertNotIn("_POP_TOP", uops)
+        self.assertIn("_POP_TOP_NOP", uops)
+
     def test_int_add_op_refcount_elimination(self):
         def testfunc(n):
             c = 1

Include/internal/pycore_uop_ids.h

@@ -0,0 +1 @@
+Eliminate redundant refcounting from ``_LOAD_ATTR_SLOT``.

Include/internal/pycore_uop_metadata.h

@@ -2485,7 +2485,7 @@ dummy_func(
             unused/5 +
             _PUSH_NULL_CONDITIONAL;
 
-        op(_LOAD_ATTR_SLOT, (index/1, owner -- attr)) {
+        op(_LOAD_ATTR_SLOT, (index/1, owner -- attr, o)) {
             PyObject *owner_o = PyStackRef_AsPyObjectBorrow(owner);
 
             PyObject **addr = (PyObject **)((char *)owner_o + index);
@@ -2498,13 +2498,16 @@ dummy_func(
             attr = PyStackRef_FromPyObjectNew(attr_o);
             #endif
             STAT_INC(LOAD_ATTR, hit);
+            o = owner;
+            DEAD(owner);
             DECREF_INPUTS();
         }
 
         macro(LOAD_ATTR_SLOT) =
             unused/1 +
             _GUARD_TYPE_VERSION +
             _LOAD_ATTR_SLOT +  // NOTE: This action may also deopt
+            POP_TOP +
             unused/5 +
             _PUSH_NULL_CONDITIONAL;
 

Lib/test/test_capi/test_opt.py

@@ -661,9 +661,10 @@ dummy_func(void) {
         o = owner;
     }
 
-    op(_LOAD_ATTR_SLOT, (index/1, owner -- attr)) {
+    op(_LOAD_ATTR_SLOT, (index/1, owner -- attr, o)) {
         attr = sym_new_not_null(ctx);
         (void)index;
+        o = owner;
     }
 
     op(_LOAD_ATTR_CLASS, (descr/4, owner -- attr)) {