gh-144540: Eliminate _MAKE_HEAP_FUNCTION for owned references

[Sacul0457]

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

[cocolato]

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.”

[cocolato]

Mark also reminded me in the last PR: #144414 (review).

[Fidget-Spinner]

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.

[cocolato]

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