Merge branch 'main' into manjusaka/gh107398

Author: serhiy-storchaka

Include/internal/pycore_magic_number.h

@@ -298,6 +298,7 @@ Known values:
     Python 3.15a8 3665 (Add FOR_ITER_VIRTUAL and GET_ITER specializations)
     Python 3.15b1 3666 (Add SEND_VIRTUAL and SEND_ASYNC_GEN specializations)
     Python 3.16a0 3700 (Initial version)
+    Python 3.16a0 3701 (Add CONSTANT_EMPTY_TUPLE to LOAD_COMMON_CONSTANT)
 
 
     Python 3.17 will start with 3750
@@ -311,7 +312,7 @@ PC/launcher.c must also be updated.
 
 */
 
-#define PYC_MAGIC_NUMBER 3700
+#define PYC_MAGIC_NUMBER 3701
 /* 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_utils.h

@@ -81,7 +81,8 @@ extern "C" {
 #define CONSTANT_FALSE 10
 #define CONSTANT_MINUS_ONE 11
 #define CONSTANT_BUILTIN_FROZENSET 12
-#define NUM_COMMON_CONSTANTS 13
+#define CONSTANT_EMPTY_TUPLE 13
+#define NUM_COMMON_CONSTANTS 14
 
 /* Values used in the oparg for RESUME */
 #define RESUME_AT_FUNC_START 0

Include/internal/pycore_optimizer.h

@@ -31,9 +31,8 @@ extern "C" {
  * 4. A push followed by a matching return is net-zero on frame-specific
  *    fitness, excluding per-slot costs.
  */
-#define MAX_TARGET_LENGTH          (UOP_MAX_TRACE_LENGTH / 2)
 #define OPTIMIZER_EFFECTIVENESS    2
-#define FITNESS_INITIAL            (MAX_TARGET_LENGTH * OPTIMIZER_EFFECTIVENESS)
+#define MAX_TARGET_LENGTH          (FITNESS_INITIAL / OPTIMIZER_EFFECTIVENESS)
 
 /* Exit quality thresholds: trace stops when fitness < exit_quality.
  * Higher = trace is more willing to stop here. */

Include/internal/pycore_uop.h

@@ -36,14 +36,18 @@ typedef struct _PyUOpInstruction{
 #endif
 } _PyUOpInstruction;
 
-// This is the length of the trace we translate initially.
+// Fitness is the target length of the trace we translate initially. The uop
+// buffer has a small amount of extra space for entry/loop-closing overhead.
 #if defined(Py_DEBUG) && defined(_Py_JIT)
     // With asserts, the stencils are a lot larger
-#define UOP_MAX_TRACE_LENGTH 1000
+#define FITNESS_INITIAL 1000
 #else
-#define UOP_MAX_TRACE_LENGTH 2500
+#define FITNESS_INITIAL 2500
 #endif
 
+#define UOP_TRACE_BUFFER_OVERHEAD 10
+#define UOP_MAX_TRACE_LENGTH (FITNESS_INITIAL + UOP_TRACE_BUFFER_OVERHEAD)
+
 /* Bloom filter with m = 256
  * https://en.wikipedia.org/wiki/Bloom_filter */
 #ifdef HAVE_GCC_UINT128_T

Lib/dis.py

@@ -698,8 +698,8 @@ def _get_const_value(op, arg, co_consts):
     if op == LOAD_SMALL_INT:
         return arg
     if op == LOAD_COMMON_CONSTANT:
-        # Opargs 0-6 are callables; 7-11 are literal values.
-        if 7 <= arg <= 11:
+        # Opargs 0-6 and 12 are callables; 7-11 and 13 are literal values.
+        if 7 <= arg <= 11 or arg == 13:
             return _common_constants[arg]
         return UNKNOWN
     argval = UNKNOWN

Lib/opcode.py

@@ -44,7 +44,7 @@
                      builtins.set,
                      # Append-only — must match CONSTANT_* in
                      # Include/internal/pycore_opcode_utils.h.
-                     None, "", True, False, -1, builtins.frozenset]
+                     None, "", True, False, -1, builtins.frozenset, ()]
 _nb_ops = _opcode.get_nb_ops()
 
 hascompare = [opmap["COMPARE_OP"]]

Lib/test/test_capi/test_opt.py

@@ -5924,6 +5924,44 @@ def __next__(self):
         """), PYTHON_JIT="1", PYTHON_JIT_STRESS="1")
         self.assertEqual(result[0].rc, 0, result)
 
+    def test_149335_trace_buffer_guard(self):
+        # https://github.com/python/cpython/issues/149335
+
+        result = script_helper.run_python_until_end('-c', textwrap.dedent("""
+        import sys
+
+        def f1():
+            for i_3178 in 0, 2, 10:
+                mv162 = 162
+
+            mv3 = mv1 = mv_165 = mv16 = \
+            mv167 = mv168 = \
+            mv169 = \
+                mv_1403_170 = \
+                169
+
+            mv_1403_170
+
+            mv_172 = mv_3 = mv_4 = mv175 = mv176 = mv17 = mv178 = mv179 = mv0 = mv1 = mv182 = (
+            mv3
+            ) = mv4 = mv185 = mv186 = mv187 = mv18 = mv189 = mv0 = mv1 = mv192 = mv3 = mv4 = (
+            mv195
+            ) = mv196 = mv197 = mv_198 = mv19 = mv0 = mv1 = mv2 = mv3 = mv4 = mv05 = mv06 = (
+            mv07
+            ) = mv08 = mv09 = mv0 = mv1 = mv2 = mv3 = mv4 = mv15 = mv16 = mv17 = mv18 = mv19 = (
+            mv0
+            ) = mv1 = mv_2 = mv3 = mv4 = mv_25 = mv_26 = mv_27 = mv_28 = mv_29 = mv0 = mv1 = (
+            mv2
+            ) = mv_1403 = mv4 = mv35 = mv36 = mv37 = mv38 = mv39 = mv0 = -sys.maxsize / 3
+
+            mv1 = mv_12 = mv3 = mv_14 = mv45 = sys.float_info.epsilon
+            mv46 = sys.float_info.epsilon
+
+        for i in range(15000):
+            f1()
+        """), PYTHON_JIT="1")
+        self.assertEqual(result[0].rc, 0, result)
+
     def test_144068_daemon_thread_jit_cleanup(self):
         result = script_helper.run_python_until_end('-c', textwrap.dedent("""
         import threading

Lib/test/test_peepholer.py

@@ -1307,10 +1307,10 @@ def test_build_empty_tuple(self):
             ('RETURN_VALUE', None, 0),
         ]
         after = [
-            ('LOAD_CONST', 0, 0),
+            ('LOAD_COMMON_CONSTANT', opcode._common_constants.index(()), 0),
             ('RETURN_VALUE', None, 0),
         ]
-        self.cfg_optimization_test(before, after, consts=[], expected_consts=[()])
+        self.cfg_optimization_test(before, after, consts=[], expected_consts=[])
 
     def test_fold_tuple_of_constants(self):
         before = [
@@ -1365,10 +1365,10 @@ def test_fold_constant_intrinsic_list_to_tuple(self):
             ('RETURN_VALUE', None, 0)
         ]
         after = [
-            ('LOAD_CONST', 0, 0),
+            ('LOAD_COMMON_CONSTANT', opcode._common_constants.index(()), 0),
             ('RETURN_VALUE', None, 0)
         ]
-        self.cfg_optimization_test(before, after, consts=[], expected_consts=[()])
+        self.cfg_optimization_test(before, after, consts=[], expected_consts=[])
 
         # multiple BUILD_LIST 0: ([], 1, [], 2)
         same = [

Misc/NEWS.d/next/Core_and_Builtins/2026-05-11-18-20-41.gh-issue-148871.AeCbq7.rst

@@ -0,0 +1,3 @@
+The empty tuple ``()`` is now loaded via :opcode:`LOAD_COMMON_CONSTANT`
+instead of :opcode:`LOAD_CONST`, removing it from per-code-object
+:attr:`~codeobject.co_consts` tuples.

Python/flowgraph.c

@@ -1468,6 +1468,10 @@ maybe_instr_make_load_common_const(cfg_instr *instr, PyObject *newconst)
              && PyUnicode_GET_LENGTH(newconst) == 0) {
         oparg = CONSTANT_EMPTY_STR;
     }
+    else if (PyTuple_CheckExact(newconst)
+             && PyTuple_GET_SIZE(newconst) == 0) {
+        oparg = CONSTANT_EMPTY_TUPLE;
+    }
     else if (PyLong_CheckExact(newconst)) {
         int overflow;
         long val = PyLong_AsLongAndOverflow(newconst, &overflow);