[Dwarf-Discuss] address pool + offset representation

Robinson, Paul paul.robinson at sony.com
Mon Aug 21 16:33:38 PDT 2017


>>> I don't really know just how much LLDB cares about fixed-size forms/DIEs,
>>> but rumor has it it's important to some degree, so I continue to have a
>>> slight preference towards fixed size representations (or at least having
>>> the option to do so, even if there are variable length forms too - as
>>> with addrx).
>>
>> Greg Clayton has told me it's a performance win for loading .debug_info.
>> They can index fixed-size DIEs without actually parsing them.  When I
>> proposed the fixed-size strx/addrx forms to the committee, I did some
>> data collection on the effect of strx and addrx.  Converting to strx
>> meant fixed size DIEs went from 90-ish to 55-ish percent of all DIEs,
>> so fixed-size strxN forms were definitely worthwhile.  The equivalent
>> analysis for addrx showed a difference of more like 4%, which was
>> enough to persuade the committee that would be worthwhile also.
>
> I imagine the same would be true of ranges in an optimized build? (Maybe
> a little lower, but not by much) 'spose, as you say, we can always add
> rnglistxN in the future.
 
It could be helpful there, I did not try to do any measurements.
--paulr



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