[lld] r248106 - COFF: Fix race condition.

[Rui Ueyama via llvm-commits]

We can, but I think we don't have to, because I didn't see any measurable
difference between this code and the old racy one.
2015/09/20 18:32 "Sean Silva" <chisophugis at gmail.com>:

> It seems unfortunate for us to need any synchronization at all just to
> generate a unique ID. Can we just have a bunch of counters, one per thread,
> then initialize them to `ThreadIndex << 50` or something? (make sure they
> are each on their own cache line)
>
> -- Sean Silva
>
> On Sat, Sep 19, 2015 at 6:44 PM, Rui Ueyama via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>> Author: ruiu
>> Date: Sat Sep 19 20:44:44 2015
>> New Revision: 248106
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=248106&view=rev
>> Log:
>> COFF: Fix race condition.
>>
>> NextID is updated inside parallel_for_each, so it needs mutual exclusion.
>>
>> Modified:
>>     lld/trunk/COFF/ICF.cpp
>>
>> Modified: lld/trunk/COFF/ICF.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/ICF.cpp?rev=248106&r1=248105&r2=248106&view=diff
>>
>> ==============================================================================
>> --- lld/trunk/COFF/ICF.cpp (original)
>> +++ lld/trunk/COFF/ICF.cpp Sat Sep 19 20:44:44 2015
>> @@ -73,7 +73,7 @@ private:
>>    bool forEachGroup(std::vector<SectionChunk *> &Chunks, Comparator Eq);
>>    bool partition(ChunkIterator Begin, ChunkIterator End, Comparator Eq);
>>
>> -  uint64_t NextID = 1;
>> +  std::atomic<uint64_t> NextID = { 1 };
>>  };
>>
>>  // Entry point to ICF.
>>
>>
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>
>
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