Duplicated lookup on unicodekeys_lookup_unicode

[corona10]

There are duplicated lookups on unicodekeys_lookup_unicode.
I am trying to understand this code as manual loop unrolling for performance. but I am not sure that it is intended.

cpython/Objects/dictobject.c

Lines 932 to 961 in be0c106

	ix = dictkeys_get_index(dk, i);
	if (ix >= 0) {
	PyDictUnicodeEntry *ep = &ep0[ix];
	assert(ep->me_key != NULL);
	assert(PyUnicode_CheckExact(ep->me_key));
	if (ep->me_key == key ||
	(unicode_get_hash(ep->me_key) == hash && unicode_eq(ep->me_key, key))) {
	return ix;
	}
	}
	else if (ix == DKIX_EMPTY) {
	return DKIX_EMPTY;
	}
	perturb >>= PERTURB_SHIFT;
	i = mask & (i*5 + perturb + 1);
	ix = dictkeys_get_index(dk, i);
	if (ix >= 0) {
	PyDictUnicodeEntry *ep = &ep0[ix];
	assert(ep->me_key != NULL);
	assert(PyUnicode_CheckExact(ep->me_key));
	if (ep->me_key == key ||
	(unicode_get_hash(ep->me_key) == hash && unicode_eq(ep->me_key, key))) {
	return ix;
	}
	}
	else if (ix == DKIX_EMPTY) {
	return DKIX_EMPTY;
	}
	perturb >>= PERTURB_SHIFT;
	i = mask & (i*5 + perturb + 1);

First introduced from f8a95df

Please let me know this that is intended.

Linked PRs

• gh-104717: Remove duplicated lookup from unicodekeys_lookup_unicode #104716
• gh-104717: Add comment about manual loop unrolling #104718

[corona10]

cc @markshannon @methane

[methane]

Yes, this is intended, manual loop unrolling.
This is the hottest path in dictobject.c.
I don't remember tha actual number of performance gain, but I had confirmed that this had some gain.

[corona10]

Okay then I will close the issue.

Yes, this is intended, manual loop unrolling.

It will be great if there is a comment about this.