[llvm-dwp] - Reuse object::Decompressor class

[grimar]

Summary

I am working on a patch to change zlib API to return Error
and just found one this place where Decompressor can also be reused.

test/tools/llvm-dwp/X86/compressfail.test

 RUN: not llvm-dwp %p/../Inputs/compressfail/a.dwo -o %t 2>&1 | FileCheck %s
 RUN: not llvm-dwp %p/../Inputs/empty_compressed_section.dwo -o %t 2>&1 | FileCheck %s
 RUN: not llvm-dwp %p/../Inputs/invalid_compressed.dwo -o %t 2>&1 | FileCheck %s
 
 REQUIRES: zlib
 
-CHECK: error: failure while decompressing compressed section: 'zdebug_{{.*}}.dwo'
+CHECK: error: failure while decompressing compressed section: '.zdebug_{{.*}}.dwo'

test/tools/llvm-dwp/X86/nocompress.test

 RUN: not llvm-dwp %p/../Inputs/compress/a.dwo -o %t 2>&1 | FileCheck %s
 
 REQUIRES: nozlib
 
-CHECK: error: zlib not available
+CHECK: error: failure while decompressing compressed section: '.zdebug_{{.*}}.dwo', zlib is not available

tools/llvm-dwp/llvm-dwp.cpp

 #include "llvm/MC/MCAsmInfo.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCInstrInfo.h"
 #include "llvm/MC/MCObjectFileInfo.h"
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/MC/MCSectionELF.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCTargetOptionsCommandFlags.h"
+#include "llvm/Object/Decompressor.h"
 #include "llvm/Object/ObjectFile.h"
 #include "llvm/Support/Compression.h"
 #include "llvm/Support/DataExtractor.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Options.h"
writeIndex(MCStreamer &Out, MCSection *Section,
   // Write the offsets.
   writeIndexTable(Out, ContributionOffsets, IndexEntries,
                   &DWARFUnitIndex::Entry::SectionContribution::Offset);
 
   // Write the lengths.
   writeIndexTable(Out, ContributionOffsets, IndexEntries,
                   &DWARFUnitIndex::Entry::SectionContribution::Length);
 }
-static bool consumeCompressedDebugSectionHeader(StringRef &data,
-                                                uint64_t &OriginalSize) {
-  // Consume "ZLIB" prefix.
-  if (!data.startswith("ZLIB"))
-    return false;
-  data = data.substr(4);
-  // Consume uncompressed section size (big-endian 8 bytes).
-  DataExtractor extractor(data, false, 8);
-  uint32_t Offset = 0;
-  OriginalSize = extractor.getU64(&Offset);
-  if (Offset == 0)
-    return false;
-  data = data.substr(Offset);
-  return true;
-}
 
 std::string buildDWODescription(StringRef Name, StringRef DWPName, StringRef DWOName) {
   std::string Text = "\'";
   Text += Name;
   Text += '\'';
   if (!DWPName.empty()) {
     Text += " (from ";
     if (!DWOName.empty()) {
       Text += '\'';
       Text += DWOName;
       Text += "' in ";
     }
     Text += '\'';
     Text += DWPName;
     Text += "')";
   }
   return Text;
 }
 
-static Error handleCompressedSection(
-    std::deque<SmallString<32>> &UncompressedSections, StringRef &Name,
-    StringRef &Contents) {
-  if (!Name.startswith("zdebug_"))
-    return Error::success();
-  UncompressedSections.emplace_back();
-  uint64_t OriginalSize;
-  if (!zlib::isAvailable())
-    return make_error<DWPError>("zlib not available");
-  if (!consumeCompressedDebugSectionHeader(Contents, OriginalSize) ||
-      zlib::uncompress(Contents, UncompressedSections.back(), OriginalSize) !=
-          zlib::StatusOK)
-    return make_error<DWPError>(
-        ("failure while decompressing compressed section: '" + Name + "\'")
-            .str());
-  Name = Name.substr(1);
+static Error createError(StringRef Name, Error E) {
+      ("failure while decompressing compressed section: '" + Name + "', " +
+       llvm::toString(std::move(E)))
+}
+
+static Error
+handleCompressedSection(std::deque<SmallString<32>> &UncompressedSections,
+                        StringRef &Name, StringRef &Contents) {
+  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();
+  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();
 }
 
 static Error handleSection(
     const StringMap<std::pair<MCSection *, DWARFSectionKind>> &KnownSections,
     const MCSection *StrSection, const MCSection *StrOffsetSection,
     const MCSection *TypesSection, const MCSection *CUIndexSection,
static Error handleSection(
 
   if (Section.isVirtual())
     return Error::success();
 
   StringRef Name;
   if (std::error_code Err = Section.getName(Name))
     return errorCodeToError(Err);
 
-  Name = Name.substr(Name.find_first_not_of("._"));
-
   StringRef Contents;
   if (auto Err = Section.getContents(Contents))
     return errorCodeToError(Err);
 
   if (auto Err = handleCompressedSection(UncompressedSections, Name, Contents))
     return Err;
 
+  Name = Name.substr(Name.find_first_not_of("._"));
+
   auto SectionPair = KnownSections.find(Name);
   if (SectionPair == KnownSections.end())
     return Error::success();
 
   if (DWARFSectionKind Kind = SectionPair->second.second) {
     auto Index = Kind - DW_SECT_INFO;
     if (Kind != DW_SECT_TYPES) {
       CurEntry.Contributions[Index].Offset = ContributionOffsets[Index];