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GeezerVison is showing github.com — gh-144540: Eliminate `_MAKE_HEAP_FUNCTION` for owned references by Sacul0457 · Pull Request #146320 · python/cpython

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@Sacul0457

@Sacul0457 Sacul0457 commented Mar 23, 2026 •
edited by bedevere-app Bot
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If the reference of the returned object is not borrowed, we remove the _MAKE_HEAP_FUNCTION. Hence I ended up changing the test_make_heap_safe_optimized_owned test to test that _MAKE_HEAP_FUNCTION is no longer in the trace as the value returned is not a borrowed reference.

Also, for a "return of a return", given the inner function returns a borrowed reference, the double _MAKE_HEAP_FUNCTION is reduced to just 1 :)

  44 OPTIMIZED: _MAKE_HEAP_SAFE_r11 (0, target=3, operand0=0, operand1=0)
  45 OPTIMIZED: _RETURN_VALUE_r11 (0, target=3, operand0=0, operand1=0)
  46 OPTIMIZED: _CHECK_VALIDITY_r11 (0, jump_target=71, operand0=0, operand1=0)
  47 OPTIMIZED: _SET_IP_r11 (0, target=10, operand0=0x1b5f9947d24, operand1=0)
  48 OPTIMIZED: _RETURN_VALUE_r11 (0, target=10, operand0=0, operand1=0)

I hope I didn't misunderstand the issue...

  • Issue: Optimize reference tracking and eliminate branching during returns and yields #144540

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@Sacul0457
optimize _MAKE_HEAP_FUNCTION for owned references
d5e9fdb
@Sacul0457
Sacul0457 requested review from Fidget-Spinner, markshannon, savannahostrowski and tomasr8 as code owners March 23, 2026 07:48
@bedevere-app bedevere-app Bot mentioned this pull request Mar 23, 2026
Optimize reference tracking and eliminate branching during returns and yields #144540
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@bedevere-app bedevere-app Bot added the awaiting review label Mar 23, 2026
@cocolato

cocolato commented Mar 23, 2026

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I think this might be a problem because in creation functions such as sym_new_not_null and sym_new_unknown, :

cpython/Python/optimizer_symbols.c

Lines 690 to 709 in fb8d8d9

JitOptRef
_Py_uop_sym_new_unknown(JitOptContext *ctx)
{
JitOptSymbol *res = sym_new(ctx);
if (res == NULL) {
return out_of_space_ref(ctx);
}
return PyJitRef_Wrap(res);
}
JitOptRef
_Py_uop_sym_new_not_null(JitOptContext *ctx)
{
JitOptSymbol *res = sym_new(ctx);
if (res == NULL) {
return out_of_space_ref(ctx);
}
res->tag = JIT_SYM_NON_NULL_TAG;
return PyJitRef_Wrap(res);
}

PyJitRef_Wrap produces a ref with tag = 0.
This means that tag = 0 is the default state, indicating “we have no specific information about borrowing/ownership,” rather than “definitely owned.” Only those explicitly marked with tag = 1 via PyJitRef_Borrow() are “known to be borrowed.”
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@cocolato

cocolato commented Mar 23, 2026

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Mark also reminded me in the last PR: #144414 (review).
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@Fidget-Spinner

Fidget-Spinner commented Mar 23, 2026

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Hmm Mark is indeed right. However, currently the only place that can generate borrowed references are LOAD_FAST_BORROW. I suspect we need to create a new tag bit for this to work.

We only support good perf on 64 bit systems right now. I propose we drop the 32 bit Windows support so that we have 3 tag bits to use and can support "unknown" references.
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@cocolato

cocolato commented Mar 23, 2026

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I propose we drop the 32 bit Windows support so that we have 3 tag bits to use and can support "unknown" references.

I also don’t think it’s necessary to maintain the performance of legacy systems
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@Sacul0457

Sacul0457 commented Mar 23, 2026

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I guess I'll mark this PR as draft for now until that is in?
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@Sacul0457
Sacul0457 marked this pull request as draft March 23, 2026 12:00
@bedevere-app bedevere-app Bot removed the awaiting review label Mar 23, 2026
@github-actions

github-actions Bot commented May 8, 2026

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This PR is stale because it has been open for 30 days with no activity.
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@github-actions github-actions Bot added the stale Stale PR or inactive for long period of time. label May 8, 2026
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@markshannon markshannon Awaiting requested review from markshannon markshannon is a code owner
@tomasr8 tomasr8 Awaiting requested review from tomasr8 tomasr8 is a code owner
@Fidget-Spinner Fidget-Spinner Awaiting requested review from Fidget-Spinner Fidget-Spinner is a code owner
@savannahostrowski savannahostrowski Awaiting requested review from savannahostrowski

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@Sacul0457 @cocolato @Fidget-Spinner
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