Reduce some code sizes

まだ誰も着手していません。

In a release build without PGO or LTO, Python's .text segment is over 5 MB.

$ size ./python
   text    data     bss     dec     hex filename
5726491  829744  468280 7024515  6b2f83 ./python

Much of this size is necessary, but some code can be reduced significantly with only small changes to code generation. Reducing the amount of code may improve the efficiency of CPU resources such as the instruction cache and branch prediction structures.

The following are the results of having Codex investigate the top 25 functions.

Largest functions in CPython

Top 25 functions in the rebuilt ./python on main, before merging the bytes and 1-byte Unicode decimal-output paths.

Sizes are function symbol sizes in bytes, obtained with readelf --symbols --wide ./python and sorted in descending order. They include inlined code but exclude separately stored data tables and out-of-line callees. The comments summarize the main reasons for the code size, based on the source and inline debug information.

Rank	Function	Bytes	Why it is large
1	`_PyEval_EvalFrameDefault`	61,487	Main bytecode interpreter: many instructions and specialized variants, with inlined stack and reference-count operations.
2	`add_ast_annotations`	49,036	Generated code repeats type construction, dictionary insertion, cleanup, and error handling for every AST field.
3	`obj2ast_stmt`	31,029	Converts Python AST objects into internal statement nodes, with separate field validation and conversion for each statement type.
4	`long_to_decimal_string_internal`	24,989	Decimal digit output is duplicated for bytes and 1-, 2-, and 4-byte Unicode representations, with substantial SIMD expansion.
5	`obj2ast_expr`	20,585	The expression counterpart: many expression types, each with its own attribute checks and conversion logic.
6	`type_ready`	20,027	Many type-initialization helpers are inlined, especially the extensive slot-inheritance logic in `inherit_slots`.
7	`sre_ucs2_match`	17,008	Complete regex matching engine for 2-byte characters, including repetition, backtracking, and inlined character-set checks.
8	`sre_ucs4_match`	16,341	A separately compiled copy of the regex matching engine for 4-byte characters.
9	`sre_ucs1_match`	16,288	A separately compiled copy of the regex matching engine for 1-byte characters.
10	`_PyConfig_Read`	15,804	Command-line parsing, environment processing, encoding configuration, and other initialization helpers are extensively inlined.
11	`ast2obj_stmt.part.0`	15,590	Builds Python AST objects from internal statements, with repeated attribute assignments and inlined list conversions.
12	`_PyAST_Fini`	13,914	Generated `Py_CLEAR` operations individually expand reference-count checks and cleanup for many AST state fields.
13	`errno_exec`	13,753	Registers many errno constants individually; the `_add_errcode` helper is inlined at repeated call sites.
14	`_PyUnicode_ToNumeric`	13,106	A generated switch maps a large, sparse set of Unicode code points to numeric values.
15	`init_types`	12,346	Generated initialization for all AST classes and operator singletons, plus inlined identifier initialization.
16	`split`	12,249	Inlines whitespace and separator splitting for ASCII and 1-, 2-, and 4-byte Unicode representations.
17	`replace`	12,168	Handles several replacement strategies and character-width conversions, with inlined search and counting routines.
18	`r_object`	12,135	Main marshal decoder: handles many object types, nested containers, code objects, and shared-reference reconstruction.
19	`PyUnicode_Format`	11,388	Inlines `%` format parsing, argument conversion, padding, width, and precision handling.
20	`codegen_visit_expr_impl`	11,387	Compiles many expression types, with inlined helpers for calls, method-call optimization, subscripts, and string construction.
21	`_PyUnicode_InitGlobalObjects`	11,154	Contains generated static-string interning calls and inlined initialization of the global table and interpreter intern dictionary.
22	`simple_stmt_rule`	9,764	Generated parser alternatives inline several statement rules, particularly imports, plus lookahead, backtracking, and syntax-error handling.
23	`codegen_visit_stmt`	9,732	Dispatches statement compilation and inlines helpers for imports, assignments, returns, and pattern matching.
24	`compound_stmt_rule`	9,705	Inlines substantial parsing logic for `with`, `match`, `try`, and `for`, including invalid-syntax rules.
25	`_PyLexer_get_normal`	9,681	Combines token recognition, indentation handling, and identifier validation with inlined character-reading and buffer-refill logic.

Linked PRs

gh-157393
gh-157483
gh-157531

まず、記載されているリンク先のPR（gh-157393、gh-157483、gh-157531）と、再ビルドした ./python で報告されている上位関数を確認します。readelf --symbols --wide と size を使用して、どの関数がリリースビルドの大部分を占めているかを特定します。PGO や LTO を使わずに .text セグメントを削減し、既存の動作を維持できれば完了です。

索引モデルが issue の本文から書いたものです。

説明

Largest functions in CPython

Linked PRs

コントリビューションガイド

はじめの一歩

調査の方向性

評価

Reduce some code sizes

説明

Largest functions in CPython

Linked PRs

コントリビューションガイド

はじめの一歩

調査の方向性

評価

新しい issue をメールで受け取る