gh-146381: Constant-fold frozendict subscript lookups via REPLACE_OPCODE_IF_EVALUATES_PURE by corona10 · Pull Request #146490 · python/cpython

corona10 · 2026-03-26T20:32:55Z

Issue: Fold _BINARY_OP_SUBSCR_DICT for promoted frozendict constants #146381

…EN_DICT

corona10 · 2026-03-26T20:50:17Z

@Fidget-Spinner
I added _BINARY_OP_SUBSCR_FROZEN_DICT as a lowered uop for frozendict lookups. When the optimizer sees _BINARY_OP_SUBSCR_DICT with a frozendict operand, it replaces it with _BINARY_OP_SUBSCR_FROZEN_DICT, then folds the result to a constant via sym_frozendict_getitem if both dict and key are known constants.

corona10 · 2026-03-26T20:54:36Z

main

['_START_EXECUTOR', '_MAKE_WARM', '_SET_IP', '_CHECK_PERIODIC', '_CHECK_VALIDITY', '_ITER_CHECK_RANGE', '_GUARD_NOT_EXHAUSTED_RANGE', '_ITER_NEXT_RANGE', '_SET_IP', '_SWAP_FAST_2', '_SPILL_OR_RELOAD', '_POP_TOP', '_CHECK_VALIDITY', '_GUARD_GLOBALS_VERSION', '_LOAD_CONST_INLINE', '_LOAD_CONST_INLINE_BORROW', '_SET_IP', '_BINARY_OP_SUBSCR_DICT', '_POP_TOP_NOP', '_SPILL_OR_RELOAD', '_POP_TOP', '_CHECK_VALIDITY', '_LOAD_CONST_INLINE_BORROW', '_GUARD_NOS_INT', '_COMPARE_OP_INT', '_POP_TOP_NOP', '_POP_TOP_INT', '_GUARD_BIT_IS_SET_POP_5', '_LOAD_FAST_BORROW_1', '_LOAD_CONST_INLINE_BORROW', '_GUARD_NOS_INT', '_BINARY_OP_ADD_INT', '_POP_TOP_NOP', '_POP_TOP_NOP', '_SWAP_FAST_1', '_POP_TOP_INT', '_JUMP_TO_TOP', '_DEOPT', '_ERROR_POP_N', '_DEOPT', '_EXIT_TRACE', '_EXIT_TRACE', '_ERROR_POP_N', '_DEOPT', '_ERROR_POP_N', '_DEOPT', '_EXIT_TRACE', '_EXIT_TRACE', '_EXIT_TRACE']

PR

['_START_EXECUTOR', '_MAKE_WARM', '_SET_IP', '_CHECK_PERIODIC', '_CHECK_VALIDITY', '_ITER_CHECK_RANGE', '_GUARD_NOT_EXHAUSTED_RANGE', '_ITER_NEXT_RANGE', '_SET_IP', '_SWAP_FAST_2', '_SPILL_OR_RELOAD', '_POP_TOP', '_CHECK_VALIDITY', '_GUARD_GLOBALS_VERSION', '_LOAD_CONST_INLINE', '_LOAD_CONST_INLINE_BORROW', '_SET_IP', '_BINARY_OP_SUBSCR_FROZEN_DICT', '_POP_TOP_NOP', '_SPILL_OR_RELOAD', '_POP_TOP', '_CHECK_VALIDITY', '_LOAD_CONST_INLINE_BORROW', '_INSERT_2_LOAD_CONST_INLINE_BORROW', '_POP_TOP_NOP', '_POP_TOP_INT', '_SET_IP', '_POP_TOP', '_CHECK_VALIDITY', '_LOAD_FAST_BORROW_1', '_LOAD_CONST_INLINE_BORROW', '_GUARD_NOS_INT', '_BINARY_OP_ADD_INT', '_POP_TOP_NOP', '_POP_TOP_NOP', '_SWAP_FAST_1', '_POP_TOP_INT', '_JUMP_TO_TOP', '_DEOPT', '_ERROR_POP_N', '_DEOPT', '_EXIT_TRACE', '_EXIT_TRACE', '_ERROR_POP_N', '_DEOPT', '_ERROR_POP_N', '_DEOPT', '_DEOPT', '_EXIT_TRACE']

Fidget-Spinner · 2026-03-27T08:53:28Z

Include/internal/pycore_optimizer.h

 extern PyTypeObject *_Py_uop_sym_get_type(JitOptRef sym);
 extern JitOptRef _Py_uop_sym_new_tuple(JitOptContext *ctx, int size, JitOptRef *args);
 extern JitOptRef _Py_uop_sym_tuple_getitem(JitOptContext *ctx, JitOptRef sym, Py_ssize_t item);
+extern JitOptRef _Py_uop_sym_frozendict_getitem(JitOptContext *ctx, JitOptRef sym, JitOptRef key);


I don't think we need this function.

Fidget-Spinner · 2026-03-27T08:53:39Z

Python/optimizer_symbols.c

    return _Py_uop_sym_new_not_null(ctx);
 }

+JitOptRef


Same here, we don't need this function.

Fidget-Spinner · 2026-03-27T08:54:40Z

Python/optimizer_bytecodes.c

+            REPLACE_OP(this_instr, _BINARY_OP_SUBSCR_FROZEN_DICT, oparg, 0);
+            res = sym_frozendict_getitem(ctx, dict_st, sub_st);


Suggested change

REPLACE_OP(this_instr, _BINARY_OP_SUBSCR_FROZEN_DICT, oparg, 0);

res = sym_frozendict_getitem(ctx, dict_st, sub_st);

REPLACE_OPCODE_IF_EVALUATES_PURE(dict_st, sub_st, res);

Check out what is the generated code in executor_cases.c.h after this :).

Fidget-Spinner · 2026-03-27T08:54:48Z

Python/optimizer_bytecodes.c

+    op(_BINARY_OP_SUBSCR_FROZEN_DICT, (dict_st, sub_st -- res, ds, ss)) {
+        res = sym_new_not_null(ctx);
+        ds = dict_st;
+        ss = sub_st;
+        REPLACE_OPCODE_IF_EVALUATES_PURE(dict_st, sub_st, res);
    }


This can be removed.

Fidget-Spinner · 2026-03-27T08:55:13Z

Lib/test/test_capi/test_opt.py

+        self.assertEqual(res, TIER2_THRESHOLD)
+        self.assertIsNotNone(ex)
+        uops = get_opnames(ex)
+        self.assertIn("_BINARY_OP_SUBSCR_FROZEN_DICT", uops)


After the correct replacement, this should just become POP_TOP_LOAD_CONST...

corona10 · 2026-03-27T16:20:56Z

@Fidget-Spinner
I've addressed your code review.
uops are optimized very well! Awesome :)

['_START_EXECUTOR', '_MAKE_WARM', '_SET_IP', '_CHECK_PERIODIC', '_CHECK_VALIDITY', '_ITER_CHECK_RANGE', '_GUARD_NOT_EXHAUSTED_RANGE', '_ITER_NEXT_RANGE', '_SET_IP', '_SWAP_FAST_2', '_SPILL_OR_RELOAD', '_POP_TOP', '_CHECK_VALIDITY', '_GUARD_GLOBALS_VERSION', '_LOAD_CONST_INLINE', '_LOAD_CONST_INLINE_BORROW', '_SET_IP', '_INSERT_2_LOAD_CONST_INLINE_BORROW', '_POP_TOP_NOP', '_SPILL_OR_RELOAD', '_POP_TOP', '_CHECK_VALIDITY', '_LOAD_CONST_INLINE_BORROW', '_INSERT_2_LOAD_CONST_INLINE_BORROW', '_POP_TOP_NOP', '_POP_TOP_INT', '_SET_IP', '_POP_TOP', '_CHECK_VALIDITY', '_LOAD_FAST_BORROW_1', '_LOAD_CONST_INLINE_BORROW', '_GUARD_NOS_INT', '_BINARY_OP_ADD_INT', '_POP_TOP_NOP', '_POP_TOP_NOP', '_SWAP_FAST_1', '_POP_TOP_INT', '_JUMP_TO_TOP', '_DEOPT', '_ERROR_POP_N', '_DEOPT', '_EXIT_TRACE', '_EXIT_TRACE', '_ERROR_POP_N', '_DEOPT', '_DEOPT', '_DEOPT', '_EXIT_TRACE']

Fidget-Spinner

The power of the JIT optimizer :).

bedevere-bot · 2026-03-28T01:27:15Z

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 Windows PGO NoGIL Tailcall 3.x (tier-1) has failed when building commit 5992238.

What do you need to do:

Don't panic.
Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/1871/builds/270) and take a look at the build logs.
Check if the failure is related to this commit (5992238) or if it is a false positive.
If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/1871/builds/270

Failed tests:

test_profiling

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "C:\bbarea\3.x.itamaro-win64-srv-22-aws.nogil.tailcall.pgo\build\Lib\test\test_profiling\test_sampling_profiler\test_advanced.py", line 169, in test_native_frames_enabled
    self.assertFalse(any(stack.endswith(";<native>") for stack in stacks))
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: True is not false

Dustin4444

#146544

corona10 added 2 commits March 27, 2026 05:31

pythongh-146381: Fold frozendict subscript via _BINARY_OP_SUBSCR_FROZ…

098ac8b

…EN_DICT

nit

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corona10 requested review from Fidget-Spinner, markshannon, savannahostrowski and tomasr8 as code owners March 26, 2026 20:32

bedevere-app bot mentioned this pull request Mar 26, 2026

Fold _BINARY_OP_SUBSCR_DICT for promoted frozendict constants #146381

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bedevere-app bot added the awaiting core review label Mar 26, 2026

nit

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corona10 added the skip news label Mar 26, 2026

Fidget-Spinner reviewed Mar 27, 2026

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corona10 changed the title ~~gh-146381: Fold frozendict subscript via _BINARY_OP_SUBSCR_FROZEN_DICT~~ gh-146381: Constant-fold frozendict subscript lookups via REPLACE_OPCODE_IF_EVALUATES_PURE Mar 27, 2026

corona10 requested a review from Fidget-Spinner March 27, 2026 16:26

Fidget-Spinner approved these changes Mar 27, 2026

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bedevere-app bot added awaiting merge and removed awaiting core review labels Mar 27, 2026

corona10 merged commit 5992238 into python:main Mar 28, 2026
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bedevere-app bot removed the awaiting merge label Mar 28, 2026

corona10 deleted the gh-146381-jit branch March 28, 2026 00:49

Dustin4444 reviewed Mar 28, 2026

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corona10 mentioned this pull request Mar 28, 2026

gh-146381: Constant fold local frozendict subscript lookups via recording #146564

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gh-146381: Constant-fold frozendict subscript lookups via REPLACE_OPCODE_IF_EVALUATES_PURE#146490

gh-146381: Constant-fold frozendict subscript lookups via REPLACE_OPCODE_IF_EVALUATES_PURE#146490
corona10 merged 4 commits intopython:mainfrom
corona10:gh-146381-jit

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		REPLACE_OP(this_instr, _BINARY_OP_SUBSCR_FROZEN_DICT, oparg, 0);
		res = sym_frozendict_getitem(ctx, dict_st, sub_st);

	REPLACE_OP(this_instr, _BINARY_OP_SUBSCR_FROZEN_DICT, oparg, 0);
	res = sym_frozendict_getitem(ctx, dict_st, sub_st);
	REPLACE_OPCODE_IF_EVALUATES_PURE(dict_st, sub_st, res);

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