[pdb] Change ghash section to use 8-byte ghashes instead of 20 byte

[zturner]

Summary

The previous algorithm used 20-byte SHA1 hashes. This new version computes the same 20-byte SHA1, but only uses the last 8 bytes as a hash.

This speeds up /DEBUG:GHASH links by ~10% in my testing while also making object files smaller.

[rnk]

lgtm

lld/COFF/PDB.cpp

 static bool canUseDebugH(ArrayRef<uint8_t> DebugH) {
   if (DebugH.size() < sizeof(object::debug_h_header))
     return false;
   auto *Header =
       reinterpret_cast<const object::debug_h_header *>(DebugH.data());
   DebugH = DebugH.drop_front(sizeof(object::debug_h_header));
   return Header->Magic == COFF::DEBUG_HASHES_SECTION_MAGIC &&
          Header->Version == 0 &&
-         Header->HashAlgorithm == uint16_t(GlobalTypeHashAlg::SHA1) &&
-         (DebugH.size() % 20 == 0);
+         Header->HashAlgorithm == uint16_t(GlobalTypeHashAlg::SHA1_8) &&
+         (DebugH.size() % 8 == 0);
 }
 
 static Optional<ArrayRef<uint8_t>> getDebugH(ObjFile *File) {
   SectionChunk *Sec = findByName(File->getDebugChunks(), ".debug$H");
   if (!Sec)
     return llvm::None;
   ArrayRef<uint8_t> Contents = Sec->getContents();
   if (!canUseDebugH(Contents))

lld/test/COFF/Inputs/pdb-hashes-1.yaml

- Name:            .text
     SectionData:     5589E583EC088B4508894DFC8B4DFC8B550889118945F889C883C4085DC20400
   - Name:            .drectve
     Characteristics: [ IMAGE_SCN_LNK_INFO, IMAGE_SCN_LNK_REMOVE ]
     Alignment:       1
     SectionData:     202F44454641554C544C49423A6C6962636D742E6C6962202F44454641554C544C49423A6F6C646E616D65732E6C6962
   - Name:            '.debug$S'
     Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_DISCARDABLE, IMAGE_SCN_MEM_READ ]
     Alignment:       4
-    SectionData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
+    SectionData:     04000000F10000002F0000002D003C110100000007000700000000000000581B000000000000636C616E672076657273696F6E20372E302E30200000F50000008400000000000000000000004100000000000000080000000000000052000000070000000400000001000000400000000000000008000000000000007F0000000600040000000000030000003E000000000000000800000000000000BD0000000400040000000000040000003D000000000000000800000000000000FA0000000300080000000000F1000000960000002A00471100000000000000000000000041000000000000000000000003100000000000000000006D61696E000D003E1174000000010061726763001200451116000000080000001700000000002A000D003E11001000000100617267760012004511160000000C0000001700000000002A000A003E1109100000000066001200451116000000F4FFFFFF1700000000002A0002004F110000F200000030000000000000000000000041000000000000000300000024000000000000000300000017000000040000003000000005000000F1000000100000000E000811091000004E533A3A466F6F00F40000003000000001000000100165C9E387F88362A8EB2B49539DD5A65500002B00000010019303CF100D518DAF59C31DA01FEF4AFC0000F30000004801000000443A5C7372635C6C6C766D6275696C645C636C616E675C44656275675C7838365C6F626A312E63707000443A5C7372635C6C6C766D6275696C645C636C616E675C44656275675C7838365C6F626A2E6800245430202E7261536561726368203D202465697020245430205E203D2024657370202454302034202B203D2000245430202E7261536561726368203D202465697020245430205E203D2024657370202454302034202B203D2024656270202454302034202D205E203D200024543020246562702034202B203D202465697020245430205E203D2024657370202454302034202B203D2024656270202454302034202D205E203D200024543020246562702034202B203D202465697020245430205E203D2024657370202454302034202B203D2024656270202454302034202D205E203D2024657369202454302038202D205E203D2000
     Subsections:
       - !Symbols
         Records:
           - Kind:            S_COMPILE3
             Compile3Sym:
               Flags:           [  ]
               Machine:         Pentium3
-              FrontendMajor:   6
+              FrontendMajor:   7
               FrontendMinor:   0
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               FrontendQFE:     0
-              BackendMajor:    6000
+              BackendMajor:    7000
               BackendMinor:    0
               BackendBuild:    0
               BackendQFE:      0
-              Version:         'clang version 6.0.0 '
+              Version:         'clang version 7.0.0 '
       - !FrameData
         Frames:
           - CodeSize:        65
             FrameFunc:       '$T0 .raSearch = $eip $T0 ^ = $esp $T0 4 + = '
             LocalSize:       0
             MaxStackSize:    0
             ParamsSize:      8
             PrologSize:      7
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               Flags:           [  ]
               DisplayName:     main
           - Kind:            S_LOCAL
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         Flags:           [  ]
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Types:
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         MemberFuncId:
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           FunctionType:    4103
           Name:            Foo
   - Name:            '.debug$H'
     Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_DISCARDABLE, IMAGE_SCN_MEM_READ ]
     Alignment:       4
-    SectionData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
+    SectionData:     C5C9330100000000E09E6E9DA0F4EE31AC3421E42389A5FD09DDDA6CB66C9F2301B4ACFA70BEACA162A1FB04917E597564A062B1FCB9248A5549419E78044E38A21119B34CB7250BC3EB8F545517B7B6CD4A36E4657A592117E12E8873BBA90CCAAE80925A1C70DA770F9F3EC6DDF03D
     GlobalHashes:
       Version:         0
       HashAlgorithm:   0
       HashValues:
-        - 9E56666824DC4B12E25261D4E09E6E9DA0F4EE31
-        - FDEC3D2D96287486127C66070B248ED52E421F55
-        - 074AE5CC2D68AF9F0A3BEF23993968F7FD82CA84
-        - BF0439C1A64C9070C6A6ADB0A34D21DAD0FFC3E9
-        - 9E616EF06A14EA74A2420F9062A1FB04917E5975
-        - E3A50EABE5E8FE3945468547C19DC681D0BFB3B7
-        - 97DD91CA4D7F1953C314442D5549419E78044E38
-        - A0BF16BFFAA5EE9C0103E7DBFE9941E63379C0B0
-        - C0A9021B711ACC4F67008974EBF441031BDD653F
-        - 6935DFF3112C6A5346EF2AC94B9B7EB56EF55CFA
-        - 0AF6C1846743F43D846BB19517E12E8873BBA90C
-        - C41DD1BEAC89CBA8897AC1BA46762E2557A82D89
-        - 4CEAE81AEF8680D723D403D9A4481F0E28683A98
+        - E09E6E9DA0F4EE31
+        - AC3421E42389A5FD
+        - 09DDDA6CB66C9F23
+        - 01B4ACFA70BEACA1
+        - 62A1FB04917E5975
+        - 64A062B1FCB9248A
+        - 5549419E78044E38
+        - A21119B34CB7250B
+        - C3EB8F545517B7B6
+        - CD4A36E4657A5921
+        - 17E12E8873BBA90C
+        - CAAE80925A1C70DA
+        - 770F9F3EC6DDF03D
   - Name:            '.debug$S'
     Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_DISCARDABLE, IMAGE_SCN_MEM_READ ]
     Alignment:       4
     SectionData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
     Subsections:
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         Frames:
           - CodeSize:        32
Subsections:
               FunctionType:    4108
               Flags:           [  ]
               DisplayName:     'NS::Foo::Foo'
           - Kind:            S_LOCAL
             LocalSym:
               Type:            4101
               Flags:           [ IsParameter ]
               VarName:         this
+          - Kind:            S_DEFRANGE_REGISTER_REL
+            DefRangeRegisterRelSym:
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     StorageClass:    IMAGE_SYM_CLASS_STATIC
     SectionDefinition:
       Length:          832
       NumberOfRelocations: 11
       NumberOfLinenumbers: 0
-      CheckSum:        4106171226
+      CheckSum:        3390759736
       Number:          6
   - Name:            '.debug$S'
     Value:           0
     SectionNumber:   9
     SimpleType:      IMAGE_SYM_TYPE_NULL
     ComplexType:     IMAGE_SYM_DTYPE_NULL
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     SimpleType:      IMAGE_SYM_TYPE_NULL
     ComplexType:     IMAGE_SYM_DTYPE_NULL
     StorageClass:    IMAGE_SYM_CLASS_STATIC
     SectionDefinition:
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       NumberOfRelocations: 0
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       Number:          8
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     SimpleType:      IMAGE_SYM_TYPE_NULL
     ComplexType:     IMAGE_SYM_DTYPE_NULL
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   - Name:            _main

lld/test/COFF/Inputs/pdb-hashes-2.yaml

- Name:            .bss
     SectionData:     ''
   - Name:            .drectve
     Characteristics: [ IMAGE_SCN_LNK_INFO, IMAGE_SCN_LNK_REMOVE ]
     Alignment:       1
     SectionData:     202F44454641554C544C49423A6C6962636D742E6C6962202F44454641554C544C49423A6F6C646E616D65732E6C6962
   - Name:            '.debug$S'
     Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_DISCARDABLE, IMAGE_SCN_MEM_READ ]
     Alignment:       4
-    SectionData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     Subsections:
       - !Symbols
         Records:
           - Kind:            S_COMPILE3
             Compile3Sym:
               Flags:           [  ]
               Machine:         Pentium3
-              FrontendMajor:   6
+              FrontendMajor:   7
               FrontendMinor:   0
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               FrontendQFE:     0
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+              BackendMajor:    7000
               BackendMinor:    0
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-              Version:         'clang version 6.0.0 '
+              Version:         'clang version 7.0.0 '
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         Frames:
           - CodeSize:        25
             FrameFunc:       '$T0 .raSearch = $eip $T0 ^ = $esp $T0 4 + = '
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               Flags:           [  ]
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           - Kind:            S_LOCAL
             LocalSym:
               Type:            4099
               Flags:           [ IsParameter ]
               VarName:         f
+          - Kind:            S_DEFRANGE_REGISTER_REL
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     Alignment:       4
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       HashAlgorithm:   0
       HashValues:
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-        - 9E616EF06A14EA74A2420F9062A1FB04917E5975
-        - 9949E334BA18509ED692F3C65CE242D8450EBC78
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-        - A0BF16BFFAA5EE9C0103E7DBFE9941E63379C0B0
-        - C0A9021B711ACC4F67008974EBF441031BDD653F
-        - 6935DFF3112C6A5346EF2AC94B9B7EB56EF55CFA
-        - 0AF6C1846743F43D846BB19517E12E8873BBA90C
-        - C41DD1BEAC89CBA8897AC1BA46762E2557A82D89
-        - DCBC783AF285D9DBB672F67A81E36906B2038B57
+        - 1132B3BB8FFACEF7
+        - 62A1FB04917E5975
+        - 3DA2762F3225F51A
+        - 8FA9212E3E55CADC
+        - 906D3449ACE2D416
+        - DAD6C5B5AFFA8CB1
+        - 64A062B1FCB9248A
+        - 5549419E78044E38
+        - A21119B34CB7250B
+        - C3EB8F545517B7B6
+        - CD4A36E4657A5921
+        - 17E12E8873BBA90C
+        - CAAE80925A1C70DA
+        - 860C83C14160CAC4
 symbols:
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     Value:           0
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     SimpleType:      IMAGE_SYM_TYPE_NULL
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     StorageClass:    IMAGE_SYM_CLASS_STATIC
     SectionDefinition:
       Length:          584
       NumberOfRelocations: 7
       NumberOfLinenumbers: 0
-      CheckSum:        2847177244
+      CheckSum:        917356735
       Number:          5
   - Name:            '.debug$T'
     Value:           0
     SectionNumber:   6
     SimpleType:      IMAGE_SYM_TYPE_NULL
     ComplexType:     IMAGE_SYM_DTYPE_NULL
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     StorageClass:    IMAGE_SYM_CLASS_STATIC
     SectionDefinition:
-      Length:          288
+      Length:          120
       NumberOfRelocations: 0
       NumberOfLinenumbers: 0
-      CheckSum:        2348181452
+      CheckSum:        2047444147
       Number:          7
   - Name:            '@feat.00'
     Value:           1
     SectionNumber:   -1
     SimpleType:      IMAGE_SYM_TYPE_NULL
     ComplexType:     IMAGE_SYM_DTYPE_NULL
     StorageClass:    IMAGE_SYM_CLASS_STATIC
   - Name:            '?func@NS@@YAHABUFoo@1@@Z'
     Value:           0
     SectionNumber:   1
     SimpleType:      IMAGE_SYM_TYPE_NULL
     ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
     StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
 ...

llvm/include/llvm/DebugInfo/CodeView/TypeHashing.h

hashTypeCollection(TypeCollection &Types) {
     std::vector<LocallyHashedType> Hashes;
     Types.ForEachRecord([&Hashes](TypeIndex TI, const CVType &Type) {
       Hashes.push_back(hashType(Type.RecordData));
     });
     return Hashes;
   }
 };
 
-enum class GlobalTypeHashAlg : uint16_t { SHA1 = 0 };
+enum class GlobalTypeHashAlg : uint16_t {
+  SHA1 = 0,  // standard 20-byte SHA1 hash
+  SHA1_8     // last 8-bytes of standard SHA1 hash
+};
 
 /// A globally hashed type represents a hash value that is sufficient to
 /// uniquely identify a record across multiple type streams or type sequences.
 /// This works by, for any given record A which references B, replacing the
 /// TypeIndex that refers to B with a previously-computed global hash for B.  As
 /// this is a recursive algorithm (e.g. the global hash of B also depends on the
 /// global hashes of the types that B refers to), a global hash can uniquely
 /// identify identify that A occurs in another stream that has a completely
 /// different graph structure.  Although the hash itself is slower to compute,
 /// probing is much faster with a globally hashed type, because the hash itself
 /// is considered "as good as" the original type.  Since type records can be
 /// quite large, this makes the equality comparison of the hash much faster than
 /// equality comparison of a full record.
 struct GloballyHashedType {
   GloballyHashedType() = default;
   GloballyHashedType(StringRef H)
       : GloballyHashedType(ArrayRef<uint8_t>(H.bytes_begin(), H.bytes_end())) {}
   GloballyHashedType(ArrayRef<uint8_t> H) {
-    assert(H.size() == 20);
-    ::memcpy(Hash.data(), H.data(), 20);
+    assert(H.size() == 8);
+    ::memcpy(Hash.data(), H.data(), 8);
   }
-  std::array<uint8_t, 20> Hash;
+  std::array<uint8_t, 8> Hash;
 
   /// Given a sequence of bytes representing a record, compute a global hash for
   /// this record.  Due to the nature of global hashes incorporating the hashes
   /// of referenced records, this function requires a list of types and ids
   /// that RecordData might reference, indexable by TypeIndex.
   static GloballyHashedType hashType(ArrayRef<uint8_t> RecordData,
                                      ArrayRef<GloballyHashedType> PreviousTypes,
                                      ArrayRef<GloballyHashedType> PreviousIds);

llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

void CodeViewDebug::emitTypeGlobalHashes() {
   OS.SwitchSection(Asm->getObjFileLowering().getCOFFGlobalTypeHashesSection());
 
   OS.EmitValueToAlignment(4);
   OS.AddComment("Magic");
   OS.EmitIntValue(COFF::DEBUG_HASHES_SECTION_MAGIC, 4);
   OS.AddComment("Section Version");
   OS.EmitIntValue(0, 2);
   OS.AddComment("Hash Algorithm");
-  OS.EmitIntValue(uint16_t(GlobalTypeHashAlg::SHA1), 2);
+  OS.EmitIntValue(uint16_t(GlobalTypeHashAlg::SHA1_8), 2);
 
   TypeIndex TI(TypeIndex::FirstNonSimpleIndex);
   for (const auto &GHR : TypeTable.hashes()) {
     if (OS.isVerboseAsm()) {
       // Emit an EOL-comment describing which TypeIndex this hash corresponds
       // to, as well as the stringified SHA1 hash.
       SmallString<32> Comment;
       raw_svector_ostream CommentOS(Comment);
       CommentOS << formatv("{0:X+} [{1}]", TI.getIndex(), GHR);
       OS.AddComment(Comment);
       ++TI;
     }
-    assert(GHR.Hash.size() % 20 == 0);
+    assert(GHR.Hash.size() == 8);
     StringRef S(reinterpret_cast<const char *>(GHR.Hash.data()),
                 GHR.Hash.size());
     OS.EmitBinaryData(S);
   }
 }
 
 static SourceLanguage MapDWLangToCVLang(unsigned DWLang) {
   switch (DWLang) {

llvm/lib/DebugInfo/CodeView/TypeHashing.cpp

 #include "llvm/Support/SHA1.h"
 
 using namespace llvm;
 using namespace llvm::codeview;
 
 LocallyHashedType DenseMapInfo<LocallyHashedType>::Empty{0, {}};
 LocallyHashedType DenseMapInfo<LocallyHashedType>::Tombstone{hash_code(-1), {}};
 
-static std::array<uint8_t, 20> EmptyHash;
-static std::array<uint8_t, 20> TombstoneHash = {
-    {0xFF, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
-     0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00}};
+static std::array<uint8_t, 8> EmptyHash = { {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00} };
+static std::array<uint8_t, 8> TombstoneHash = {
+  {0xFF, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00} };
 
 GloballyHashedType DenseMapInfo<GloballyHashedType>::Empty{EmptyHash};
 GloballyHashedType DenseMapInfo<GloballyHashedType>::Tombstone{TombstoneHash};
 
 LocallyHashedType LocallyHashedType::hashType(ArrayRef<uint8_t> RecordData) {
   return {llvm::hash_value(RecordData), RecordData};
 }
 
for (const auto &Ref : Refs) {
 
     Off = Ref.Offset + Ref.Count * sizeof(TypeIndex);
   }
 
   // Don't forget to add in any trailing bytes.
   auto TrailingBytes = RecordData.drop_front(Off);
   S.update(TrailingBytes);
 
-  return {S.final()};
+  return {S.final().take_back(8)};
 }

llvm/lib/ObjectYAML/CodeViewYAMLTypeHashing.cpp

StringRef ScalarTraits<GlobalHash>::input(StringRef Scalar, void *Ctx,
   return ScalarTraits<BinaryRef>::input(Scalar, Ctx, GH.Hash);
 }
 
 } // end namespace yaml
 } // end namespace llvm
 
 DebugHSection llvm::CodeViewYAML::fromDebugH(ArrayRef<uint8_t> DebugH) {
   assert(DebugH.size() >= 8);
-  assert((DebugH.size() - 8) % 20 == 0);
+  assert((DebugH.size() - 8) % 8 == 0);
 
   BinaryStreamReader Reader(DebugH, llvm::support::little);
   DebugHSection DHS;
   cantFail(Reader.readInteger(DHS.Magic));
   cantFail(Reader.readInteger(DHS.Version));
   cantFail(Reader.readInteger(DHS.HashAlgorithm));
   while (Reader.bytesRemaining() != 0) {
     ArrayRef<uint8_t> S;
-    cantFail(Reader.readBytes(S, 20));
+    cantFail(Reader.readBytes(S, 8));
     DHS.Hashes.emplace_back(S);
   }
   assert(Reader.bytesRemaining() == 0);
   return DHS;
 }
 
 ArrayRef<uint8_t> llvm::CodeViewYAML::toDebugH(const DebugHSection &DebugH,
                                                BumpPtrAllocator &Alloc) {
-  uint32_t Size = 8 + 20 * DebugH.Hashes.size();
+  uint32_t Size = 8 + 8 * DebugH.Hashes.size();
   uint8_t *Data = Alloc.Allocate<uint8_t>(Size);
   MutableArrayRef<uint8_t> Buffer(Data, Size);
   BinaryStreamWriter Writer(Buffer, llvm::support::little);
   cantFail(Writer.writeInteger(DebugH.Magic));
   cantFail(Writer.writeInteger(DebugH.Version));
   cantFail(Writer.writeInteger(DebugH.HashAlgorithm));
-  SmallString<20> Hash;
+  SmallString<8> Hash;
   for (const auto &H : DebugH.Hashes) {
     Hash.clear();
     raw_svector_ostream OS(Hash);
     H.Hash.writeAsBinary(OS);
-    assert((Hash.size() == 20) && "Invalid hash size!");
+    assert((Hash.size() == 8) && "Invalid hash size!");
     cantFail(Writer.writeFixedString(Hash));
   }
   assert(Writer.bytesRemaining() == 0);
   return Buffer;
 }

llvm/test/DebugInfo/COFF/global-type-hashes.ll

 ; YAML:           ClassType:       4100
 ; YAML:           FunctionType:    4105
 ; YAML:           Name:            method
 ; YAML:   - Name:            '.debug$H'
 ; YAML:     Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_DISCARDABLE, IMAGE_SCN_MEM_READ ]
 ; YAML:     Alignment:       4
 ; YAML:     GlobalHashes:
 ; YAML:       Version:         0
-; YAML:       HashAlgorithm:   0
+; YAML:       HashAlgorithm:   1
 ; YAML:       HashValues:
-; YAML:         - 9E56666824DC4B12E25261D4E09E6E9DA0F4EE31
-; YAML:         - FDEC3D2D96287486127C66070B248ED52E421F55
-; YAML:         - 074AE5CC2D68AF9F0A3BEF23993968F7FD82CA84
-; YAML:         - BF0439C1A64C9070C6A6ADB0A34D21DAD0FFC3E9
-; YAML:         - CF1B3AD4A96BA628E6556FD28A222FBBEBBE140E
-; YAML:         - EC50195BFE148C0DC6A87A59D49CA1D9B146DB86
-; YAML:         - 123C8BA63AD23386897AB6D814A9932F03846156
-; YAML:         - 0F135243878289B83835BC2DB9EE25A1D4D0DA2B
-; YAML:         - 9069CA78E7450A285173431B3E52C5C25299E473
-; YAML:         - ADA6E11350E9F2069D4689E3646C90D67B28DA62
-; YAML:         - BD535FA9877A4DD123840AF849F3B0110EEB1D7A
-; YAML:         - 8044F70193FE40B71867158C5E50F0467485FA99
-; YAML:         - 558606D57A76D125B705FC6DD18EEE3C1C0C4C09
-; YAML:         - A64A018D9EB1EB8015917925662C8508D81CDA68
-; YAML:         - 51E89AD9992AC6F11F9E3F1665F41C53BDA8AFC4
-; YAML:         - 4F1C3BCA73099EF3466AAC99CC4951767DF890F5
+; YAML:         - E09E6E9DA0F4EE31
+; YAML:         - AC3421E42389A5FD
+; YAML:         - 09DDDA6CB66C9F23
+; YAML:         - 01B4ACFA70BEACA1
+; YAML:         - 8A222FBBEBBE140E
+; YAML:         - 4497C6AE188A6220
+; YAML:         - 14A9932F03846156
+; YAML:         - CBC539F8C18B2D2D
+; YAML:         - 3E52C5C25299E473
+; YAML:         - 8FEE74F5141FCC22
+; YAML:         - DF48EB0A8ED58F85
+; YAML:         - 8EE98BB0F291CBF8
+; YAML:         - D18EEE3C1C0C4C09
+; YAML:         - 67C712E2108F482A
+; YAML:         - 23945F2B63311976
+; YAML:         - 7F1CACD4255A7ADF
 ; ...
 
 
 ; ASM:      .section        .debug$H,"dr"
 ; ASM-NEXT: .p2align        2
 ; ASM-NEXT: .long   20171205                # Magic
 ; ASM-NEXT: .short  0                       # Section Version
-; ASM-NEXT: .short  0                       # Hash Algorithm
-; ASM-NEXT: .byte   0x9e, 0x56, 0x66, 0x68  # 0x1000 [9E56666824DC4B12E25261D4E09E6E9DA0F4EE31]
-; ASM-NEXT: .byte   0x24, 0xdc, 0x4b, 0x12
-; ASM-NEXT: .byte   0xe2, 0x52, 0x61, 0xd4
-; ASM-NEXT: .byte   0xe0, 0x9e, 0x6e, 0x9d
+; ASM-NEXT: .short  1                       # Hash Algorithm
+; ASM-NEXT: .byte   0xe0, 0x9e, 0x6e, 0x9d  # 0x1000 [E09E6E9DA0F4EE31]
 ; ASM-NEXT: .byte   0xa0, 0xf4, 0xee, 0x31
-; ASM-NEXT: .byte   0xfd, 0xec, 0x3d, 0x2d  # 0x1001 [FDEC3D2D96287486127C66070B248ED52E421F55]
-; ASM-NEXT: .byte   0x96, 0x28, 0x74, 0x86
-; ASM-NEXT: .byte   0x12, 0x7c, 0x66, 0x07
-; ASM-NEXT: .byte   0x0b, 0x24, 0x8e, 0xd5
-; ASM-NEXT: .byte   0x2e, 0x42, 0x1f, 0x55
-; ASM-NEXT: .byte   0x07, 0x4a, 0xe5, 0xcc  # 0x1002 [074AE5CC2D68AF9F0A3BEF23993968F7FD82CA84]
+; ASM-NEXT: .byte   0xac, 0x34, 0x21, 0xe4  # 0x1001 [AC3421E42389A5FD]
+; ASM-NEXT: .byte   0x23, 0x89, 0xa5, 0xfd
+; ASM-NEXT: .byte   0x09, 0xdd, 0xda, 0x6c  # 0x1002 [09DDDA6CB66C9F23]

llvm/test/DebugInfo/PDB/obj-globalhash.test

 RUN: yaml2obj %p/Inputs/obj-hashes-1.yaml > %T/obj-hashes-1.obj
 RUN: yaml2obj %p/Inputs/obj-hashes-2.yaml > %T/obj-hashes-2.obj
 RUN: echo obj-hashes-1 > %T/hashes-combined.out
 RUN: llvm-pdbutil dump -type-extras %T/obj-hashes-1.obj >> %T/hashes-combined.out
 RUN: echo obj-hashes-2 >> %T/hashes-combined.out
 RUN: llvm-pdbutil dump -type-extras %T/obj-hashes-2.obj >> %T/hashes-combined.out
 RUN: cat %T/hashes-combined.out | FileCheck --check-prefix=CHECK-ONE %s
 RUN: cat %T/hashes-combined.out | FileCheck --check-prefix=CHECK-TWO %s
 RUN: cat %T/hashes-combined.out | FileCheck --check-prefix=CHECK-THREE %s
 RUN: cat %T/hashes-combined.out | FileCheck --check-prefix=CHECK-FOUR %s
 RUN: cat %T/hashes-combined.out | FileCheck --check-prefix=CHECK-FIVE %s
 RUN: cat %T/hashes-combined.out | FileCheck --check-prefix=CHECK-SIX %s
 
 ; char**.  Both the local and global hashes should be the same, since the only
 ; back-references are for simple types which have fixed indices.
 CHECK-ONE:   obj-hashes-1
-CHECK-ONE:   TI: 0x1001, LocalHash: {{.*}}, GlobalHash: 8B2BA87CC27BF9D290A31A6070FA296AAA577E53
+CHECK-ONE:   TI: 0x1001, LocalHash: {{.*}}, GlobalHash: 70FA296AAA577E53
 CHECK-ONE:   obj-hashes-2
-CHECK-ONE:   TI: 0x1000, LocalHash: {{.*}}, GlobalHash: 8B2BA87CC27BF9D290A31A6070FA296AAA577E53
+CHECK-ONE:   TI: 0x1000, LocalHash: {{.*}}, GlobalHash: 70FA296AAA577E53
 
 ; int**.  Same as char**, both the local and global hashes should be the same.
 CHECK-TWO:   obj-hashes-1
-CHECK-TWO:   TI: 0x1000, LocalHash: {{.*}}, GlobalHash: 1522A98D88FAF71B618D97BCAC2B89A424EC4805
+CHECK-TWO:   TI: 0x1000, LocalHash: {{.*}}, GlobalHash: AC2B89A424EC4805
 CHECK-TWO:   obj-hashes-2
-CHECK-TWO:   TI: 0x1002, LocalHash: {{.*}}, GlobalHash: 1522A98D88FAF71B618D97BCAC2B89A424EC4805
+CHECK-TWO:   TI: 0x1002, LocalHash: {{.*}}, GlobalHash: AC2B89A424EC4805
 
 ; int***. Different local hashes, since the referent type (int**) is not at the
 ; same TypeIndex in both streams.  Same global hash, since they represent the
 ; same record.
 CHECK-THREE: obj-hashes-1
-CHECK-THREE: TI: 0x1002, LocalHash: {{.*}}, GlobalHash: EC11CE9F78D6BF61F8D913A9E2C98293782A7EB4
+CHECK-THREE: TI: 0x1002, LocalHash: {{.*}}, GlobalHash: 9D6275A3E1B37A7D
 CHECK-THREE: obj-hashes-2
-CHECK-THREE: TI: 0x1001, LocalHash: {{.*}}, GlobalHash: EC11CE9F78D6BF61F8D913A9E2C98293782A7EB4
+CHECK-THREE: TI: 0x1001, LocalHash: {{.*}}, GlobalHash: 9D6275A3E1B37A7D
 
 ; arg list (char**, int***).  Different local hashes, since the parameter types
 ; both occur at different TypeIndices in their respective input streams.  Same
 ; global hash, since the global hash of all referenced types is the same in
 ; both streams.
 CHECK-FOUR:  obj-hashes-1
-CHECK-FOUR:  TI: 0x1003, LocalHash: {{.*}}, GlobalHash: 1088AD64CEBC88D9E015058A159516AF20B79286
+CHECK-FOUR:  TI: 0x1003, LocalHash: {{.*}}, GlobalHash: C82DFD641EB22940
 CHECK-FOUR:  obj-hashes-2
-CHECK-FOUR:  TI: 0x1004, LocalHash: {{.*}}, GlobalHash: 1088AD64CEBC88D9E015058A159516AF20B79286
+CHECK-FOUR:  TI: 0x1004, LocalHash: {{.*}}, GlobalHash: C82DFD641EB22940
 
 ; double**.  This is only in stream 2, as a means to throw off the indexing.
 CHECK-FIVE:  obj-hashes-1
 CHECK-FIVE:  obj-hashes-2
-CHECK-FIVE:  TI: 0x1003, LocalHash: {{.*}}, GlobalHash: 7803BBDB2947EF46BEA2310D102BD08F68315506
+CHECK-FIVE:  TI: 0x1003, LocalHash: {{.*}}, GlobalHash: 102BD08F68315506
 
 ; int** (char**, int***).  For the same logic as described in previous records,
 ; these two records have the same global hash but different local hashes.
 CHECK-SIX:   obj-hashes-1
-CHECK-SIX:   TI: 0x1004, LocalHash: {{.*}}, GlobalHash: 457ABCB8AB70407594B5D72BF471B6BDECC99BC9
+CHECK-SIX:   TI: 0x1004, LocalHash: {{.*}}, GlobalHash: 526C704BC7D94D40
 CHECK-SIX:   obj-hashes-2
-CHECK-SIX:   TI: 0x1005, LocalHash: {{.*}}, GlobalHash: 457ABCB8AB70407594B5D72BF471B6BDECC99BC9
+CHECK-SIX:   TI: 0x1005, LocalHash: {{.*}}, GlobalHash: 526C704BC7D94D40

llvm/test/ObjectYAML/CodeView/sections.yaml

Types:
           Name:            'C:\src\llvm-project\build\vc140.pdb'
   - Name:            '.debug$H'
     Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_DISCARDABLE, IMAGE_SCN_MEM_READ ]
     Alignment:       4
     GlobalHashes:
       Version:          0
       HashAlgorithm:    0
       HashValues:
-        - 1522A98D88FAF71B618D97BCAC2B89A424EC4805
-        - 8B2BA87CC27BF9D290A31A6070FA296AAA577E53
-        - EC11CE9F78D6BF61F8D913A9E2C98293782A7EB4
-        - 1088AD64CEBC88D9E015058A159516AF20B79286
-        - 457ABCB8AB70407594B5D72BF471B6BDECC99BC9
+        - AC2B89A424EC4805
+        - 70FA296AAA577E53
+        - E2C98293782A7EB4
+        - 159516AF20B79286
+        - F471B6BDECC99BC9
 symbols:
   - Name:            '.debug$T'
     Value:           0
     SectionNumber:   1
     SimpleType:      IMAGE_SYM_TYPE_NULL
     ComplexType:     IMAGE_SYM_DTYPE_NULL
     StorageClass:    IMAGE_SYM_CLASS_STATIC
     SectionDefinition:

 # CHECK:           Name:            'C:\src\llvm-project\build\vc140.pdb'
 # CHECK:   - Name:            '.debug$H'
 # CHECK:     Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_DISCARDABLE, IMAGE_SCN_MEM_READ ]
 # CHECK:     Alignment:       4
 # CHECK:     GlobalHashes:
 # CHECK:       Version:          0
 # CHECK:       HashAlgorithm:    0
 # CHECK:       HashValues:
-# CHECK:         - 1522A98D88FAF71B618D97BCAC2B89A424EC4805
-# CHECK:         - 8B2BA87CC27BF9D290A31A6070FA296AAA577E53
-# CHECK:         - EC11CE9F78D6BF61F8D913A9E2C98293782A7EB4
-# CHECK:         - 1088AD64CEBC88D9E015058A159516AF20B79286
-# CHECK:         - 457ABCB8AB70407594B5D72BF471B6BDECC99BC9
+# CHECK:         - AC2B89A424EC4805
+# CHECK:         - 70FA296AAA577E53
+# CHECK:         - E2C98293782A7EB4
+# CHECK:         - 159516AF20B79286
+# CHECK:         - F471B6BDECC99BC9
 # CHECK: symbols:
 # CHECK:   - Name:            '.debug$T'
 # CHECK:     Value:           0
 # CHECK:     SectionNumber:   1
 # CHECK:     SimpleType:      IMAGE_SYM_TYPE_NULL
 # CHECK:     ComplexType:     IMAGE_SYM_DTYPE_NULL
 # CHECK:     StorageClass:    IMAGE_SYM_CLASS_STATIC
 # CHECK:     SectionDefinition:

 # CHECK:       Length:          108
 # CHECK:       NumberOfRelocations: 0
 # CHECK:       NumberOfLinenumbers: 0
 # CHECK:       CheckSum:        2189213922
 # CHECK:       Number:          1
 # CHECK: ...
 
 # HEADERS:   0 .debug$T      00000040 0000000000000000 DATA
-# HEADERS:   1 .debug$H      0000006c 0000000000000000 DATA
+# HEADERS:   1 .debug$H      00000030 0000000000000000 DATA