| From: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> |
|---|---|
| To: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Greg Stark <stark(at)mit(dot)edu>, Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: scanner/parser minimization |
| Date: | 2013-03-14 17:08:12 |
| Message-ID: | 514203FC.2090202@vmware.com |
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| Lists: | pgsql-hackers |
On 13.03.2013 10:50, Simon Riggs wrote:
> On 2 March 2013 18:47, Heikki Linnakangas<hlinnakangas(at)vmware(dot)com> wrote:
>> Interestingly, the yy_transition array generated by flex used to be much
>> smaller:
>>
>> 8.3: 22072 elements
>> 8.4: 62623 elements
>> master: 64535 elements
>>
>> The big jump between 8.3 and 8.4 was caused by introduction of the unicode
>> escapes: U&'foo' [UESCAPE 'x'] . And in particular, the "error rule" for the
>> UESCAPE, which we use to avoid backtracking.
>>
>> I experimented with a patch that uses two extra flex states to shorten the
>> error rules, see attached. The idea is that after lexing a unicode literal
>> like "U&'foo'", you enter a new state, in which you check whether an
>> "UESCAPE 'x'" follows. This slashes the size of the array to 36581 elements.
>
> +1 to do this sooner rather than later
I hear no objection, so committed. (after fixing some small bugs in the
patch, and adding some comments)
- Heikki
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