Optimize zend_string equality check with hash key

6 years ago by Benjamin Coutu — view source

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Hello,

I was surprised to find out that equality checks on zend_string do not take advantage of the fact that in many cases we have a hash key available that can be utilized in a quick bailout path without having to resort to a costly memcmp on the value.

I recommend to modify zend_string_equal_content like so:

static zend_always_inline zend_bool zend_string_equal_content(zend_string *s1, zend_string *s2)
{
if (ZSTR_LEN(s1) != ZSTR_LEN(s2)) {
return 0;
}

if (ZSTR_H(s1) && ZSTR_H(s1) != ZSTR_H(s2)) {
return 0;
}

return zend_string_equal_val(s1, s2);
}

Thoughts?

--

Benjamin Coutu
ben.coutu@zeyos.com

6 years ago by G. P. B. — view source

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Hello,

I was surprised to find out that equality checks on zend_string do not
take advantage of the fact that in many cases we have a hash key available
that can be utilized in a quick bailout path without having to resort to a
costly memcmp on the value.

I recommend to modify zend_string_equal_content like so:

static zend_always_inline zend_bool zend_string_equal_content(zend_string
*s1, zend_string *s2)
{
if (ZSTR_LEN(s1) != ZSTR_LEN(s2)) {
return 0;
}

if (ZSTR_H(s1) && ZSTR_H(s1) != ZSTR_H(s2)) {
return 0;
}

return zend_string_equal_val(s1, s2);
}

Thoughts?

--

Benjamin Coutu
ben.coutu@zeyos.com

Best idea would be to do a PR on the GitHub repo.

Best regards

George Peter Banyard

6 years ago by Andrea Faulds — view source

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Hi Benjamin,

Benjamin Coutu wrote:

if (ZSTR_H(s1) && ZSTR_H(s1) != ZSTR_H(s2)) {
return 0;
}

Should that not be like this?:

 if (ZSTR_H(s1) && ZSTR_H(s2) && ZSTR_H(s1) != ZSTR_H(s2)) {

It would be possible the other string also has no hash value.

Otherwise this sounds sensible to me, but it is also so obvious that I
was assuming until now that PHP does it, so maybe someone else knows a
reason why we don't? (Maybe it's just not worth the extra branches?)

Thanks,
Andrea