Add support for COFF groups in * Linker * compiland in PDB

[aganea]

Summary

This patch adds emitting of COFF groups to the linker compiland stored in the PDB.

Fixes bug 36277:
https://bugs.llvm.org/show_bug.cgi?id=36277

[stefan_reinalter]

Updated diff to only contain formatted changes for new code.

[zturner]

Sorry for the delay on this, been OOO. I'll take a look tomorrow.

[aganea]

Could you possibly add a test along? That would serve both as coverage & documentation about the feature.

You can maybe look at how other tests are done in lld/trunk/test/COFF/pdb-*. Let me know if any help is needed.

[aganea]

Will be closed by D54802

[aganea]

Commited as part of rL357308. Many thanks again @stefan_reinalter !

COFF/PDB.cpp

static void addCommonLinkerModuleSymbols(StringRef Path,
   Mod.addSymbol(codeview::SymbolSerializer::writeOneSymbol(
       ONS, Allocator, CodeViewContainer::Pdb));
   Mod.addSymbol(codeview::SymbolSerializer::writeOneSymbol(
       CS, Allocator, CodeViewContainer::Pdb));
   Mod.addSymbol(codeview::SymbolSerializer::writeOneSymbol(
       EBS, Allocator, CodeViewContainer::Pdb));
 }
 
+static void addLinkerModuleCoffGroup(const Chunk *firstChunk,
+                                     const Chunk *lastChunk,
+                                     pdb::DbiModuleDescriptorBuilder &Mod,
+                                     OutputSection &OS,
+                                     BumpPtrAllocator &Allocator) {
+  CoffGroupSym CGS(SymbolRecordKind::CoffGroupSym);
+  CGS.Name = firstChunk->getSectionName();
+  CGS.Segment = OS.SectionIndex;
+  CGS.Offset = firstChunk->getRVA() - OS.getRVA();
+  CGS.Size = lastChunk->getRVA() + lastChunk->getSize() - firstChunk->getRVA();
+  CGS.Characteristics = firstChunk->getOutputCharacteristics();
+  Mod.addSymbol(codeview::SymbolSerializer::writeOneSymbol(
+      CGS, Allocator, CodeViewContainer::Pdb));
+}
+
 static void addLinkerModuleSectionSymbol(pdb::DbiModuleDescriptorBuilder &Mod,
                                          OutputSection &OS,
                                          BumpPtrAllocator &Allocator) {
   SectionSym Sym(SymbolRecordKind::SectionSym);
   Sym.Alignment = 12; // 2^12 = 4KB
   Sym.Characteristics = OS.Header.Characteristics;
   Sym.Length = OS.getVirtualSize();
   Sym.Name = OS.Name;
   Sym.Rva = OS.getRVA();
   Sym.SectionNumber = OS.SectionIndex;
   Mod.addSymbol(codeview::SymbolSerializer::writeOneSymbol(
       Sym, Allocator, CodeViewContainer::Pdb));
+
+  // Output COFF groups for individual chunks of this section.
+  // There may be several chunks with the same name (e.g. .text$di), but we only
+  // want to output each unique chunk once.
+  Chunk *firstChunkInSubSection = nullptr;
+  Chunk *lastChunkInSubSection = nullptr;
+
+  for (Chunk *C : OS.getChunks()) {
+    auto *SecChunk = dyn_cast<SectionChunk>(C);
+
+    // If this chunk doesn't represent an unmerged input file chunk, or it
+    // didn't contribute to the final output file, skip it.
+    if (!SecChunk || !SecChunk->isLive())
+      continue;
+
+    if (!firstChunkInSubSection) {
+      firstChunkInSubSection = C;
+    }
+
+    if (C->getSectionName() != firstChunkInSubSection->getSectionName()) {
+      addLinkerModuleCoffGroup(firstChunkInSubSection, lastChunkInSubSection,
+                               Mod, OS, Allocator);
+
+      firstChunkInSubSection = C;
+    }
+
+    lastChunkInSubSection = C;
+  }
+
+  if (firstChunkInSubSection && lastChunkInSubSection) {
+    addLinkerModuleCoffGroup(firstChunkInSubSection, lastChunkInSubSection, Mod,
+                             OS, Allocator);
+  }
 }
 
 // Creates a PDB file.
 void coff::createPDB(SymbolTable *Symtab,
                      ArrayRef<OutputSection *> OutputSections,
                      ArrayRef<uint8_t> SectionTable,
                      const llvm::codeview::DebugInfo &BuildId) {
   ScopedTimer T1(TotalPdbLinkTimer);