[lld] r317910 - Use DenseMap instead of std::map in fixupExports

[Reid Kleckner via llvm-commits]

We don't iterate this map. I split this out of https://reviews.llvm.org/
D39609 because it seemed uncontroversial and forgot to copy the part of the
message where I mentioned that.

On Tue, Nov 14, 2017 at 12:27 AM, Rui Ueyama <ruiu at google.com> wrote:

> DenseMap's iteration order can be different depending on host's word size
> because I believe the default hash function produces different hash values
> on 32-bit than 64-bit. Does lld still produce the same output on both 32/64
> hosts?
>
> On Sat, Nov 11, 2017 at 4:12 AM, Reid Kleckner via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>> Author: rnk
>> Date: Fri Nov 10 11:12:01 2017
>> New Revision: 317910
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=317910&view=rev
>> Log:
>> Use DenseMap instead of std::map in fixupExports
>>
>> Some DLLs have many exports, and this data structure shows up in the
>> profile of linking content.dll.
>>
>> Modified:
>>     lld/trunk/COFF/DriverUtils.cpp
>>
>> Modified: lld/trunk/COFF/DriverUtils.cpp
>> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/DriverUti
>> ls.cpp?rev=317910&r1=317909&r2=317910&view=diff
>> ============================================================
>> ==================
>> --- lld/trunk/COFF/DriverUtils.cpp (original)
>> +++ lld/trunk/COFF/DriverUtils.cpp Fri Nov 10 11:12:01 2017
>> @@ -594,7 +594,7 @@ void fixupExports() {
>>    }
>>
>>    // Uniquefy by name.
>> -  std::map<StringRef, Export *> Map;
>> +  DenseMap<StringRef, Export *> Map(Config->Exports.size());
>>    std::vector<Export> V;
>>    for (Export &E : Config->Exports) {
>>      auto Pair = Map.insert(std::make_pair(E.ExportName, &E));
>>
>>
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>
>
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