History

Guido van Rossum cabd6e8a10 gh-106529: Support JUMP_BACKWARD in Tier 2 (uops) (#106543 ) During superblock generation, a JUMP_BACKWARD instruction is translated to either a JUMP_TO_TOP micro-op (when the target of the jump is exactly the beginning of the superblock, closing the loop), or a SAVE_IP + EXIT_TRACE pair, when the jump goes elsewhere. The new JUMP_TO_TOP instruction includes a CHECK_EVAL_BREAKER() call, so a closed loop can still be interrupted.		2023-07-11 18:08:10 +00:00
..
README.md	gh-104584: Baby steps towards generating and executing traces (#105924 )	2023-06-26 19:02:57 -07:00
generate_cases.py	gh-106529: Support JUMP_BACKWARD in Tier 2 (uops) (#106543 )	2023-07-11 18:08:10 +00:00
interpreter_definition.md	Update DSL docs for cases generator (#105753 )	2023-06-14 08:19:24 -07:00
lexer.py	gh-106200: Remove unused imports (#106201 )	2023-06-28 11:55:41 +00:00
parser.py	Remove support for legacy bytecode instructions (#105705 )	2023-06-12 18:19:04 +00:00
plexer.py	GH-98831: Refactor and fix cases generator (#99526 )	2022-11-17 17:06:07 -08:00
test_generator.py	gh-104584: Baby steps towards generating and executing traces (#105924 )	2023-06-26 19:02:57 -07:00

README.md

Tooling to generate interpreters

Documentation for the instruction definitions in Python/bytecodes.c ("the DSL") is here.

What's currently here:

lexer.py: lexer for C, originally written by Mark Shannon
plexer.py: OO interface on top of lexer.py; main class: PLexer
parser.py: Parser for instruction definition DSL; main class Parser
generate_cases.py: driver script to read Python/bytecodes.c and write Python/generated_cases.c.h (and several other files)
test_generator.py: tests, require manual running using pytest

Note that there is some dummy C code at the top and bottom of Python/bytecodes.c to fool text editors like VS Code into believing this is valid C code.

A bit about the parser

The parser class uses a pretty standard recursive descent scheme, but with unlimited backtracking. The PLexer class tokenizes the entire input before parsing starts. We do not run the C preprocessor. Each parsing method returns either an AST node (a Node instance) or None, or raises SyntaxError (showing the error in the C source).

Most parsing methods are decorated with @contextual, which automatically resets the tokenizer input position when None is returned. Parsing methods may also raise SyntaxError, which is irrecoverable. When a parsing method returns None, it is possible that after backtracking a different parsing method returns a valid AST.

Neither the lexer nor the parsers are complete or fully correct. Most known issues are tersely indicated by # TODO: comments. We plan to fix issues as they become relevant.