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Postings from January 2013
On 29 January 2013 12:39, David Cantrell <david@cantrell.org.uk> wrote:
> On Mon, Jan 28, 2013 at 04:24:38PM +0000, Dave Mitchell wrote:
>
>> Perl defines the LIKELY() and UNLIKELY() macros, which (under gcc)
>> tell the compiler whether a particular expression is likely to be true or
>> not...
>>
>> if (UNLIKELY(rare_condition)) {
>> .. do something rare, e.g. warn ...
>> }
>>
>> which will hopefully allow the compiler to do clever things.
>>
>> Now, my thoughts are:
>>
>> 1) Has anyone looked at this recently to know whether gcc does anything
>> useful with it?
>>
>> 2) does anyone know whether other compilers provide similar facilities,
>> and so want to contribute suitable macro defs?
>>
>> 3) if it is useful, should we be using it in lots of places?
>
> 4) is the cost in making the perl source code even more impenetrable due
> to being a twisty maze of macros worth it?
Personally I dont think this is a case of impenetrable macros. In fact
the opposite.
These macros make the developers intent more clear even if they do nothing else.
For one of my XS projects I found a modest use of them made a small
but repeatedly measurable difference.
Yves
--
perl -Mre=debug -e "/just|another|perl|hacker/"
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