Simplify PyStackRef_FromPyObjectSteal

Feature or enhancement

Currently, PyStackRef_FromPyObjectSteal checks if the object is immortal in order to set the Py_TAG_DEFERRED bit.

cpython/Include/internal/pycore_stackref.h

Lines 96 to 105 in 29cbcbd

    
           static inline _PyStackRef 
        
           _PyStackRef_FromPyObjectSteal(PyObject *obj) 
        
           { 
        
               assert(obj != NULL); 
        
               // Make sure we don't take an already tagged value. 
        
               assert(((uintptr_t)obj & Py_TAG_BITS) == 0); 
        
               unsigned int tag = _Py_IsImmortal(obj) ? (Py_TAG_DEFERRED) : Py_TAG_PTR; 
        
               return ((_PyStackRef){.bits = ((uintptr_t)(obj)) | tag}); 
        
           } 
        
           #   define PyStackRef_FromPyObjectSteal(obj) _PyStackRef_FromPyObjectSteal(_PyObject_CAST(obj))

This check isn't necessary and has a performance cost that's not made up for by the slightly faster PyStackRef_CLOSE() calls or PyStackRef_Is() checks.

We should simplify PyStackRef_FromPyObjectSteal so that it creates _PyStackRef directly from the PyObject * without setting any tag bits.

Linked PRs

pythongh-127022: Simplify `PyStackRef_FromPyObjectSteal`

I think this will also allow us to simplify or remove _PyEvalFramePushAndInit_UnTagged.

gh-127022: Simplify `PyStackRef_FromPyObjectSteal` (#127024)

pythongh-127022: Remove `_PyEvalFramePushAndInit_UnTagged`

gh-127022: Remove `_PyEvalFramePushAndInit_UnTagged` (gh-127168)

pythongh-127022: Simplify `PyStackRef_FromPyObjectSteal` (python#127024)

pythongh-127022: Remove `_PyEvalFramePushAndInit_UnTagged` (pythongh-…

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Simplify `PyStackRef_FromPyObjectSteal` #127022

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	static inline _PyStackRef
	_PyStackRef_FromPyObjectSteal(PyObject *obj)
	{
	assert(obj != NULL);
	// Make sure we don't take an already tagged value.
	assert(((uintptr_t)obj & Py_TAG_BITS) == 0);
	unsigned int tag = _Py_IsImmortal(obj) ? (Py_TAG_DEFERRED) : Py_TAG_PTR;
	return ((_PyStackRef){.bits = ((uintptr_t)(obj)) \| tag});
	}
	# define PyStackRef_FromPyObjectSteal(obj) _PyStackRef_FromPyObjectSteal(_PyObject_CAST(obj))

Simplify PyStackRef_FromPyObjectSteal #127022

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colesbury commented on Nov 19, 2024

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Simplify `PyStackRef_FromPyObjectSteal` #127022