[LLVMdev] On LLD performance

Rafael EspĂ­ndola rafael.espindola at gmail.com
Fri Mar 20 14:56:35 PDT 2015

>> > 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


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