[lib/Object] - Minor API update for llvm::Decompressor.

[grimar]

Summary

I revisited Decompressor API (issue with it was triggered during D32865 review)
and found it is probably provides more then we really need.

Issue was about next method's signature:

Error decompress(SmallString<32> &Out);

It is too strict. At first I wanted to change it to decompress(SmallVectorImpl<char> &Out),
but then found it is still not flexible because sticks to SmallVector.

During reviews was suggested to use templating to simplify code. Patch do that.

[grimar]

• Addressed review comment.

[grimar]

• Fix comment.

include/llvm/Object/Decompressor.h

public:
   /// @brief Create decompressor object.
   /// @param Name        Section name.
   /// @param Data        Section content.
   /// @param IsLE        Flag determines if Data is in little endian form.
   /// @param Is64Bit     Flag determines if object is 64 bit.
   static Expected<Decompressor> create(StringRef Name, StringRef Data,
                                        bool IsLE, bool Is64Bit);
 
-  /// @brief Resize the buffer and uncompress section data into it.
-  /// @param Out         Destination buffer.
-  Error decompress(SmallString<32> &Out);
-
   /// @brief Uncompress section data to raw buffer provided.
   /// @param Buffer      Destination buffer.
   Error decompress(MutableArrayRef<char> Buffer);
 
   /// @brief Return memory buffer size required for decompression.
   uint64_t getDecompressedSize() { return DecompressedSize; }
 
   /// @brief Return true if section is compressed, including gnu-styled case.

lib/DebugInfo/DWARF/DWARFContext.cpp

if (!Decompressor::isCompressed(Sec))
     return Error::success();
 
   Expected<Decompressor> Decompressor =
       Decompressor::create(Name, Data, IsLittleEndian, AddressSize == 8);
   if (!Decompressor)
     return Decompressor.takeError();
 
   SmallString<32> Out;
+  Out.resize(Decompressor->getDecompressedSize());
   if (auto Err = Decompressor->decompress(Out))
     return Err;
 
   UncompressedSections.emplace_back(std::move(Out));
   Data = UncompressedSections.back();
 
   return Error::success();
 }

lib/Object/Decompressor.cpp

if (Section.getName(Name))
     return false;
   return Section.isCompressed() || isGnuStyle(Name);
 }
 
 bool Decompressor::isCompressedELFSection(uint64_t Flags, StringRef Name) {
   return (Flags & ELF::SHF_COMPRESSED) || isGnuStyle(Name);
 }
 
-Error Decompressor::decompress(SmallString<32> &Out) {
-  Out.resize(DecompressedSize);
-  return decompress({Out.data(), (size_t)DecompressedSize});
-}
-
 Error Decompressor::decompress(MutableArrayRef<char> Buffer) {
   size_t Size = Buffer.size();
   return zlib::uncompress(SectionData, Buffer.data(), Size);
 }

tools/llvm-dwp/llvm-dwp.cpp

if (!Decompressor::isGnuStyle(Name))
     return Error::success();
 
   Expected<Decompressor> Dec =
       Decompressor::create(Name, Contents, false /*IsLE*/, false /*Is64Bit*/);
   if (!Dec)
     return createError(Name, Dec.takeError());
 
   UncompressedSections.emplace_back();
+  UncompressedSections.back().resize(Dec->getDecompressedSize());
   if (Error E = Dec->decompress(UncompressedSections.back()))
     return createError(Name, std::move(E));
 
   Name = Name.substr(2); // Drop ".z"
   Contents = UncompressedSections.back();
   return Error::success();
 }