Description:
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fetch_timezone_offset does a linear search through the list of time transitions. Many timezones have a rather large number of transitions. Eg, Pacific time appears to have ~180 transitions.

One possible solution might be to do a binary search rather than a linear search of the list of times. But a simpler solution could be to do a search backwards in the array: most people probably do manipulation of recent rather than old dates

I tested this using HHVM, which uses the same upstream timezone code as PHP.

Test script:
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<?
date_default_timezone_set("America/Los_Angeles");
for ($i = 0; $i < 10000000; $i ++) date('I');

Expected result:
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figuring out the DST rules should not be a perf issue

Actual result:
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perf record shows timelib_get_time_zone_info taking a substantial amount of time