[LLVMdev] On LLD performance

[Rafael Espíndola]

>> > https://people.freebsd.org/~davide/llvm/lld-03162015.svg
>> > It seems now 85% of CPU time is spent inside
>> > FileArchive::buildTableOfContents().
>> > In particular, 35% of the samples are spent inserting into
>> > unordered_map, so there's maybe something we can do differently there
>> > (e.g. , Rui's proposal of a concurrent map doesn't seem that bad).
>> >
>>
>> Why do we even need to build the table from name to member?
>>
>> Can't we just walk "archive->symbols()" and check for each symbol if
>> it is needed by the current link status?
>
>
> Are you suggesting we do linear search instead of hash table lookup each
> time ArchiveFile::find(StringRef symbolName) is called?


No, what I mean is that we only need to keep one hash of the current
state of the link (which symbols are still undefined).

Once you get to an archive, don't build a hashtable of every symbol it
provides. Instead, walk the list of symbols it provides and if one of
those is currently undefined in the global table, include it in the
link.

Cheers,
Rafael