GH-128685: Specialize (rather than quicken) LOAD_CONST into LOAD_CONST_[IM]MORTAL (GH-128708)

Author: markshannon

Include/internal/pycore_magic_number.h

@@ -265,6 +265,7 @@ Known values:
     Python 3.14a4 3610 (Add VALUE_WITH_FAKE_GLOBALS format to annotationlib)
     Python 3.14a4 3611 (Add NOT_TAKEN instruction)
     Python 3.14a4 3612 (Add POP_ITER and INSTRUMENTED_POP_ITER)
+    Python 3.14a4 3613 (Add LOAD_CONST_MORTAL instruction)
 
     Python 3.15 will start with 3650
 
@@ -277,7 +278,7 @@ PC/launcher.c must also be updated.
 
 */
 
-#define PYC_MAGIC_NUMBER 3612
+#define PYC_MAGIC_NUMBER 3613
 /* This is equivalent to converting PYC_MAGIC_NUMBER to 2 bytes
    (little-endian) and then appending b'\r\n'. */
 #define PYC_MAGIC_NUMBER_TOKEN \

Include/internal/pycore_opcode_metadata.h

@@ -892,7 +892,7 @@ def loop_test():
 %3d           RESUME_CHECK             0
 
 %3d           BUILD_LIST               0
-              LOAD_CONST               0 ((1, 2, 3))
+              LOAD_CONST_MORTAL        0 ((1, 2, 3))
               LIST_EXTEND              1
               LOAD_SMALL_INT           3
               BINARY_OP                5 (*)
@@ -2548,7 +2548,7 @@ def test_specialized_code(self):
         expect = '''
             0           RESUME                   0
 
-            1           LOAD_CONST_IMMORTAL      0 (None)
+            1           LOAD_CONST               0 (None)
                         RETURN_VALUE
         '''
         for flag in ['-S', '--specialized']:

Include/internal/pycore_uop_ids.h

@@ -285,11 +285,25 @@ dummy_func(
         }
 
         family(LOAD_CONST, 0) = {
+            LOAD_CONST_MORTAL,
             LOAD_CONST_IMMORTAL,
         };
 
-        pure inst(LOAD_CONST, (-- value)) {
-            value = PyStackRef_FromPyObjectNew(GETITEM(FRAME_CO_CONSTS, oparg));
+        inst(LOAD_CONST, (-- value)) {
+            /* We can't do this in the bytecode compiler as
+             * marshalling can intern strings and make them immortal. */
+            PyObject *obj = GETITEM(FRAME_CO_CONSTS, oparg);
+            value = PyStackRef_FromPyObjectNew(obj);
+#if ENABLE_SPECIALIZATION
+            if (this_instr->op.code == LOAD_CONST) {
+                this_instr->op.code = _Py_IsImmortal(obj) ? LOAD_CONST_IMMORTAL : LOAD_CONST_MORTAL;
+            }
+#endif
+        }
+
+        inst(LOAD_CONST_MORTAL, (-- value)) {
+            PyObject *obj = GETITEM(FRAME_CO_CONSTS, oparg);
+            value = PyStackRef_FromPyObjectNew(obj);
         }
 
         inst(LOAD_CONST_IMMORTAL, (-- value)) {