Description

Fidget-Spinner

opened on Jan 4, 2026

Issue body actions

Feature or enhancement

Proposal:

Currently the JIT uop buffer modifies uops traces in place.

I think we should make it add to a new buffer. Having modifications be in-place is making our code messy and full of special cases.

So

REPLACE_OP(this_instr, ...)

should become

ADD_OP(ctx, ...)

in optimizer_bytecodes.c,

Also, the default generated case of optimizer_bytecodes.c should be to ADD_OP(pc, ...)

This is also blocking optimization in #143414, as ocassionally we need to insert extra guards to check the uniqueness of an object for example.

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

No response

Linked PRs

• gh-143421: Move JitOptContext from stack allocation to per-thread heap allocation to avoid stack overflow. #143536
• gh-143421: Lazily allocate tracer code and opt buffers #143597
• gh-143421: Allocate all JIT state in one go #143626
• gh-143421: Use new buffer to save optimized uops #143682

Reacted by Tomas R.

Activity

1. Fidget-Spinner

   added

   type-featureA feature request or enhancementA feature request or enhancement

   topic-JIT

   on Jan 4, 2026
2. corona10

   assigned

   corona10

   and

   Fidget-Spinner

   on Jan 5, 2026
3. picnixz

   added

   interpreter-core(Objects, Python, Grammar, and Parser dirs)(Objects, Python, Grammar, and Parser dirs)

   on Jan 5, 2026
4. markshannon commented on Jan 5, 2026

   

   markshannon

   on Jan 5, 2026

   Member

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   I agree, but let's refactor the JIT structs to be heap allocated first.

   Reacted by Ken Jin
5. Fidget-Spinner commented on Jan 6, 2026

   

   Fidget-Spinner

   on Jan 6, 2026

   MemberAuthor

   More actions

   I agree, but let's refactor the JIT structs to be heap allocated first.

   Assigning this to @cocolato
6. Fidget-Spinner

   changed the title [-]Make the JIT optimizer buffer add to a new buffer, not in-place[/-] [+] JIT optimizer cleanups[/+] on Jan 6, 2026
7. Fidget-Spinner

   added 4 commits that reference this issue on Jan 8, 2026

   gh-143421: Move `JitOptContext` from stack allocation to per-thread h…

   aeb3403

   Revert "pythongh-143421: Move `JitOptContext` from stack allocation t…

   738696f

   gh-143421: Lazily allocate tracer code and opt buffers (GH-143597)

   b852236

   gh-143421: Allocate all JIT state in one go (GH-143626)

   e0fb278
8. cocolato commented on Jan 10, 2026

   

   cocolato

   on Jan 10, 2026

   Member

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   How should we handle the following case? It appears that we cannot simply use ADD_OP as a substitute. Perhaps we still need a REPLACE_OP to handle the new buffer.

   cpython/Python/optimizer_bytecodes.c

   Line 1512 in e7f5ffa

   REPLACE_OP(this_instr-1, _GUARD_GLOBALS_VERSION, 0, version);

   and

   cpython/Python/optimizer_bytecodes.c

   Line 1024 in e7f5ffa

   REPLACE_OP(this_instr+1, _NOP, 0, 0);
9. Fidget-Spinner commented on Jan 10, 2026

   

   Fidget-Spinner

   on Jan 10, 2026

   MemberAuthor

   More actions

   @cocolato make REPLACE_OP operate on the new buffer instead of the old one. Ideally you should have two buffers. An old buffer containing the current uops, and a new buffer, containing the uops being written.

   If the optimizer stops early, you can just insert an _EXIT_TRACE at that location in the new buffer.

   Reacted by Hai Zhu
10. reidenong

    added 3 commits that reference this issue on Jan 12, 2026

    pythongh-143421: Move `JitOptContext` from stack allocation to per-th…

    86e3e81

    pythongh-143421: Lazily allocate tracer code and opt buffers (pythonG…

    ac9af52

    pythongh-143421: Allocate all JIT state in one go (pythonGH-143626)

    d0fb0b4
11. Fidget-Spinner

    added a commit that references this issue on Jan 17, 2026

    gh-143421: Use new buffer to save optimized uops (GH-143682)

    b4b7324
12. Fidget-Spinner

    closed this as completedon Jan 21, 2026
13. thunder-coding

    added 4 commits that reference this issue on Feb 15, 2026

    pythongh-143421: Move `JitOptContext` from stack allocation to per-th…

    d7bb693

    pythongh-143421: Lazily allocate tracer code and opt buffers (pythonG…

    bc68e75

    pythongh-143421: Allocate all JIT state in one go (pythonGH-143626)

    f5742c8

    pythongh-143421: Use new buffer to save optimized uops (pythonGH-143682)

    f8ace70

Issue actions