Duplicated lookup on unicodekeys_lookup_unicode

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

@markshannon

cc @markshannon @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.

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Duplicated lookup on unicodekeys_lookup_unicode #104717

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	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);

Duplicated lookup on unicodekeys_lookup_unicode #104717

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corona10 commented on May 21, 2023

methane commented on May 21, 2023

corona10 commented on May 21, 2023

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