[lld] r311056 - Remove a lock and use a std::unique_ptr instead.

[Rafael Avila de Espindola via llvm-commits]

Alternativelly it can also just be a std::unique_ptr<uint8_t>, no?

Cheers,
Rafael

David Blaikie via llvm-commits <llvm-commits at lists.llvm.org> writes:

> Is it really worth/necessary to indirect this vector through a unique_ptr?
> Saves two words in the InputSection, I guess, in the common (not
> compressed) case? (could save the other word too, if you used a separate
> map to only store these things when needed)
>
> But maybe this is the sweet spot of convenience and memory usage. Just
> curious/checking :)
>
> On Wed, Aug 16, 2017 at 5:28 PM Rui Ueyama via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>> Author: ruiu
>> Date: Wed Aug 16 17:27:55 2017
>> New Revision: 311056
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=311056&view=rev
>> Log:
>> Remove a lock and use a std::unique_ptr instead.
>>
>> We had a lock to guard BAlloc from being used concurrently, but that
>> is not very easy to understand. This patch replaces it with a
>> std::unique_ptr.
>>
>> Modified:
>>     lld/trunk/ELF/InputSection.cpp
>>     lld/trunk/ELF/InputSection.h
>>
>> Modified: lld/trunk/ELF/InputSection.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/InputSection.cpp?rev=311056&r1=311055&r2=311056&view=diff
>>
>> ==============================================================================
>> --- lld/trunk/ELF/InputSection.cpp (original)
>> +++ lld/trunk/ELF/InputSection.cpp Wed Aug 16 17:27:55 2017
>> @@ -200,17 +200,12 @@ void InputSectionBase::uncompress() {
>>                                                  Config->IsLE,
>> Config->Is64));
>>
>>    size_t Size = Dec.getDecompressedSize();
>> -  char *OutputBuf;
>> -  {
>> -    static std::mutex Mu;
>> -    std::lock_guard<std::mutex> Lock(Mu);
>> -    OutputBuf = BAlloc.Allocate<char>(Size);
>> -  }
>> -
>> -  if (Error E = Dec.decompress({OutputBuf, Size}))
>> +  UncompressBuf.reset(new std::vector<uint8_t>(Size));
>> +  if (Error E = Dec.decompress({(char *)UncompressBuf->data(), Size}))
>>      fatal(toString(this) +
>>            ": decompress failed: " + llvm::toString(std::move(E)));
>> -  this->Data = ArrayRef<uint8_t>((uint8_t *)OutputBuf, Size);
>> +
>> +  this->Data = *UncompressBuf;
>>    this->Flags &= ~(uint64_t)SHF_COMPRESSED;
>>  }
>>
>>
>> Modified: lld/trunk/ELF/InputSection.h
>> URL:
>> http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/InputSection.h?rev=311056&r1=311055&r2=311056&view=diff
>>
>> ==============================================================================
>> --- lld/trunk/ELF/InputSection.h (original)
>> +++ lld/trunk/ELF/InputSection.h Wed Aug 16 17:27:55 2017
>> @@ -183,6 +183,11 @@ public:
>>      assert(S % sizeof(T) == 0);
>>      return llvm::makeArrayRef<T>((const T *)Data.data(), S / sizeof(T));
>>    }
>> +
>> +private:
>> +  // A pointer that owns uncompressed data if a section is compressed by
>> zlib.
>> +  // Since the feature is not used often, this is usually a nullptr.
>> +  std::unique_ptr<std::vector<uint8_t>> UncompressBuf;
>>  };
>>
>>  // SectionPiece represents a piece of splittable section contents.
>>
>>
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