Give InfoStreamBuilder an opt-in method to write a hash of the PDB as GUID.

Naively computing the hash after the PDB data has been generated is in practice
as fast as other approaches I tried. I also tried online-computing the hash as
parts of the PDB were written out (https://reviews.llvm.org/D51887; that's also
where all the measuring data is) and computing the hash in parallel
(https://reviews.llvm.org/D51957). This approach here is simplest, without
being slower.

Differential Revision: https://reviews.llvm.org/D51956

llvm-svn: 342333

1 files changed, 26 insertions, 7 deletions

diff --git a/llvm/lib/DebugInfo/PDB/Native/PDBFileBuilder.cpp b/llvm/lib/DebugInfo/PDB/Native/PDBFileBuilder.cpp
index 1612d74eba2..e0ceb7499ee 100644
--- a/llvm/lib/DebugInfo/PDB/Native/PDBFileBuilder.cpp
+++ b/llvm/lib/DebugInfo/PDB/Native/PDBFileBuilder.cpp
@@ -25,6 +25,7 @@
 #include "llvm/Support/BinaryStreamWriter.h"
 #include "llvm/Support/JamCRC.h"
 #include "llvm/Support/Path.h"
+#include "llvm/Support/xxhash.h"
 
 using namespace llvm;
 using namespace llvm::codeview;
@@ -261,13 +262,14 @@ void PDBFileBuilder::commitInjectedSources(WritableBinaryStream &MsfBuffer,
   }
 }
 
-Error PDBFileBuilder::commit(StringRef Filename) {
+Error PDBFileBuilder::commit(StringRef Filename, codeview::GUID *Guid) {
   assert(!Filename.empty());
   if (auto EC = finalizeMsfLayout())
     return EC;
 
   MSFLayout Layout;
-  auto ExpectedMsfBuffer = Msf->commit(Filename, Layout);
+  Expected<FileBufferByteStream> ExpectedMsfBuffer =
+      Msf->commit(Filename, Layout);
   if (!ExpectedMsfBuffer)
     return ExpectedMsfBuffer.takeError();
   FileBufferByteStream Buffer = std::move(*ExpectedMsfBuffer);
@@ -329,11 +331,28 @@ Error PDBFileBuilder::commit(StringRef Filename) {
 
   // Set the build id at the very end, after every other byte of the PDB
   // has been written.
-  // FIXME: Use a hash of the PDB rather than time(nullptr) for the signature.
-  H->Age = Info->getAge();
-  H->Guid = Info->getGuid();
-  Optional<uint32_t> Sig = Info->getSignature();
-  H->Signature = Sig.hasValue() ? *Sig : time(nullptr);
+  if (Info->hashPDBContentsToGUID()) {
+    // Compute a hash of all sections of the output file.
+    uint64_t Digest =
+        xxHash64({Buffer.getBufferStart(), Buffer.getBufferEnd()});
+
+    H->Age = 1;
+
+    memcpy(H->Guid.Guid, &Digest, 8);
+    // xxhash only gives us 8 bytes, so put some fixed data in the other half.
+    memcpy(H->Guid.Guid + 8, "LLD PDB.", 8);
+
+    // Put the hash in the Signature field too.
+    H->Signature = static_cast<uint32_t>(Digest);
+
+    // Return GUID to caller.
+    memcpy(Guid, H->Guid.Guid, 16);
+  } else {
+    H->Age = Info->getAge();
+    H->Guid = Info->getGuid();
+    Optional<uint32_t> Sig = Info->getSignature();
+    H->Signature = Sig.hasValue() ? *Sig : time(nullptr);
+  }
 
   return Buffer.commit();
 }