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

[David Blaikie via llvm-commits]

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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