[DebugInfo][PDB] Don't write empty debug streams

Before, empty debug streams were written as 8 bytes (4 bytes signature + 4 bytes for the GlobalRefs count).

With this patch, unused empty streams aren't emitted anymore. Modules now encode 65535 as an 'unused stream' value, by convention.
Also fix the * Linker * contrib section which wasn't correctly emitted previously.

Differential Revision: https://reviews.llvm.org/D59502

llvm-svn: 356395

2 files changed, 16 insertions, 6 deletions

diff --git a/llvm/lib/DebugInfo/PDB/Native/DbiModuleDescriptorBuilder.cpp b/llvm/lib/DebugInfo/PDB/Native/DbiModuleDescriptorBuilder.cpp
index 922bea765c7..20b6c614254 100644
--- a/llvm/lib/DebugInfo/PDB/Native/DbiModuleDescriptorBuilder.cpp
+++ b/llvm/lib/DebugInfo/PDB/Native/DbiModuleDescriptorBuilder.cpp
@@ -103,7 +103,6 @@ uint32_t DbiModuleDescriptorBuilder::calculateSerializedLength() const {
 }
 
 void DbiModuleDescriptorBuilder::finalize() {
-  Layout.SC.Imod = Layout.Mod;
   Layout.FileNameOffs = 0; // TODO: Fix this
   Layout.Flags = 0;        // TODO: Fix this
   Layout.C11Bytes = 0;
@@ -116,12 +115,15 @@ void DbiModuleDescriptorBuilder::finalize() {
 
   // This value includes both the signature field as well as the record bytes
   // from the symbol stream.
-  Layout.SymBytes = SymbolByteSize + sizeof(uint32_t);
+  Layout.SymBytes =
+      Layout.ModDiStream == kInvalidStreamIndex ? 0 : getNextSymbolOffset();
 }
 
 Error DbiModuleDescriptorBuilder::finalizeMsfLayout() {
   this->Layout.ModDiStream = kInvalidStreamIndex;
   uint32_t C13Size = calculateC13DebugInfoSize();
+  if (!C13Size && !SymbolByteSize)
+    return Error::success();
   auto ExpectedSN =
       MSF.addStream(calculateDiSymbolStreamSize(SymbolByteSize, C13Size));
   if (!ExpectedSN)
diff --git a/llvm/lib/DebugInfo/PDB/Native/ModuleDebugStream.cpp b/llvm/lib/DebugInfo/PDB/Native/ModuleDebugStream.cpp
index 649ff7c56ad..1445f0bd9e1 100644
--- a/llvm/lib/DebugInfo/PDB/Native/ModuleDebugStream.cpp
+++ b/llvm/lib/DebugInfo/PDB/Native/ModuleDebugStream.cpp
@@ -14,6 +14,7 @@
 #include "llvm/DebugInfo/CodeView/SymbolRecord.h"
 #include "llvm/DebugInfo/CodeView/SymbolRecordHelpers.h"
 #include "llvm/DebugInfo/PDB/Native/DbiModuleDescriptor.h"
+#include "llvm/DebugInfo/PDB/Native/RawConstants.h"
 #include "llvm/DebugInfo/PDB/Native/RawError.h"
 #include "llvm/Support/BinaryStreamReader.h"
 #include "llvm/Support/BinaryStreamRef.h"
@@ -36,6 +37,17 @@ ModuleDebugStreamRef::~ModuleDebugStreamRef() = default;
 Error ModuleDebugStreamRef::reload() {
   BinaryStreamReader Reader(*Stream);
 
+  if (Mod.getModuleStreamIndex() != llvm::pdb::kInvalidStreamIndex) {
+    if (Error E = reloadSerialize(Reader))
+      return E;
+  }
+  if (Reader.bytesRemaining() > 0)
+    return make_error<RawError>(raw_error_code::corrupt_file,
+                                "Unexpected bytes in module stream.");
+  return Error::success();
+}
+
+Error ModuleDebugStreamRef::reloadSerialize(BinaryStreamReader &Reader) {
   uint32_t SymbolSize = Mod.getSymbolDebugInfoByteSize();
   uint32_t C11Size = Mod.getC11LineInfoByteSize();
   uint32_t C13Size = Mod.getC13LineInfoByteSize();
@@ -71,10 +83,6 @@ Error ModuleDebugStreamRef::reload() {
     return EC;
   if (auto EC = Reader.readSubstream(GlobalRefsSubstream, GlobalRefsSize))
     return EC;
-  if (Reader.bytesRemaining() > 0)
-    return make_error<RawError>(raw_error_code::corrupt_file,
-                                "Unexpected bytes in module stream.");
-
   return Error::success();
 }