[CodeGen/Dwarf] Make debug_names compatible with split-dwarf

[labath]

Summary

Previously we crashed for the combination of the two features because we
tried to reference the dwo CU from the main object file. The fix
consists of two items:

• reference the skeleton CU from the name index (the consumer is expected to use the skeleton CU to find the real data).
• use the main object file string pool for the strings in the index

[aprantl]

lib/CodeGen/AsmPrinter/DwarfDebug.h

342

any kind of doxygen comment that would make sense here?

lib/CodeGen/AsmPrinter/AccelTable.cpp

Dwarf5AccelTableEmitter::getUniformAttributes() const {
   UA.push_back({dwarf::DW_IDX_die_offset, dwarf::DW_FORM_ref4});
   return UA;
 }
 
 void Dwarf5AccelTableEmitter::emitCUList() const {
   for (const auto &CU : enumerate(CompUnits)) {
     assert(CU.index() == CU.value()->getUniqueID());
     Asm->OutStreamer->AddComment("Compilation unit " + Twine(CU.index()));
-    Asm->emitDwarfSymbolReference(CU.value()->getLabelBegin());
+    const DwarfCompileUnit *MainCU =
+        DD.useSplitDwarf() ? CU.value()->getSkeleton() : CU.value().get();
+    Asm->emitDwarfSymbolReference(MainCU->getLabelBegin());
   }
 }
 
 void Dwarf5AccelTableEmitter::emitBuckets() const {
   uint32_t Index = 1;
   for (const auto &Bucket : enumerate(Contents.getBuckets())) {
     Asm->OutStreamer->AddComment("Bucket " + Twine(Bucket.index()));
     Asm->emitInt32(Bucket.value().empty() ? 0 : Index);

lib/CodeGen/AsmPrinter/DwarfDebug.h

void ensureAbstractVariableIsCreatedIfScoped(DwarfCompileUnit &CU, InlinedVariable Var,
                                                const MDNode *Scope);
 
   DbgVariable *createConcreteVariable(DwarfCompileUnit &TheCU,
                                       LexicalScope &Scope, InlinedVariable IV);
 
   /// Construct a DIE for this abstract scope.
   void constructAbstractSubprogramScopeDIE(DwarfCompileUnit &SrcCU, LexicalScope *Scope);
 
+  void addAccelDebugName(StringRef Name, const DIE &Die);
+
   void finishVariableDefinitions();
 
   void finishSubprogramDefinitions();
 
   /// Finish off debug information after all functions have been
   /// processed.
   void finalizeModuleInfo();
 

lib/CodeGen/AsmPrinter/DwarfDebug.cpp

if (TopLevelType) {
     for (auto &TU : TypeUnitsToAdd) {
       InfoHolder.computeSizeAndOffsetsForUnit(TU.first.get());
       InfoHolder.emitUnit(TU.first.get(), useSplitDwarf());
     }
   }
   CU.addDIETypeSignature(RefDie, Signature);
 }
 
+void DwarfDebug::addAccelDebugName(StringRef Name, const DIE &Die) {
+  assert(getAccelTableKind() == AccelTableKind::Dwarf);
+
+  DwarfFile &Holder = useSplitDwarf() ? SkeletonHolder : InfoHolder;
+  AccelDebugNames.addName(Holder.getStringPool().getEntry(*Asm, Name), Die);
+}
+
 // Accelerator table mutators - add each name along with its companion
 // DIE to the proper table while ensuring that the name that we're going
 // to reference is in the string table. We do this since the names we
 // add may not only be identical to the names in the DIE.
 void DwarfDebug::addAccelName(StringRef Name, const DIE &Die) {
   switch (getAccelTableKind()) {
   case AccelTableKind::Apple:
     AccelNames.addName(InfoHolder.getStringPool().getEntry(*Asm, Name), &Die);
     break;
   case AccelTableKind::Dwarf:
-    AccelDebugNames.addName(InfoHolder.getStringPool().getEntry(*Asm, Name),
-                            Die);
+    addAccelDebugName(Name, Die);
     break;
   case AccelTableKind::None:
     return;
   case AccelTableKind::Default:
     llvm_unreachable("Default should have already been resolved.");
   }
 }
 
 void DwarfDebug::addAccelObjC(StringRef Name, const DIE &Die) {
   if (getAccelTableKind() != AccelTableKind::Apple)
     return;
   AccelObjC.addName(InfoHolder.getStringPool().getEntry(*Asm, Name), &Die);
 }
 
 void DwarfDebug::addAccelNamespace(StringRef Name, const DIE &Die) {
   switch (getAccelTableKind()) {
   case AccelTableKind::Apple:
     AccelNamespace.addName(InfoHolder.getStringPool().getEntry(*Asm, Name),
                            &Die);
     break;
   case AccelTableKind::Dwarf:
-    AccelDebugNames.addName(InfoHolder.getStringPool().getEntry(*Asm, Name),
-                            Die);
+    addAccelDebugName(Name, Die);
     break;
   case AccelTableKind::None:
     return;
   case AccelTableKind::Default:
     llvm_unreachable("Default should have already been resolved.");
   }
 }
 
 void DwarfDebug::addAccelType(StringRef Name, const DIE &Die, char Flags) {
   switch (getAccelTableKind()) {
   case AccelTableKind::Apple:
     AccelTypes.addName(InfoHolder.getStringPool().getEntry(*Asm, Name), &Die);
     break;
   case AccelTableKind::Dwarf:
-    AccelDebugNames.addName(InfoHolder.getStringPool().getEntry(*Asm, Name),
-                            Die);
+    addAccelDebugName(Name, Die);
     break;
   case AccelTableKind::None:
     return;
   case AccelTableKind::Default:
     llvm_unreachable("Default should have already been resolved.");
   }
 }
 
 uint16_t DwarfDebug::getDwarfVersion() const {
   return Asm->OutStreamer->getContext().getDwarfVersion();
 }

test/DebugInfo/Generic/debug-names-one-cu.ll

 ; REQUIRES: object-emission
 ; RUN: %llc_dwarf -accel-tables=Dwarf -filetype=obj -o %t < %s
 ; RUN: llvm-dwarfdump -debug-names %t | FileCheck %s
 ; RUN: llvm-dwarfdump -debug-names -verify %t | FileCheck --check-prefix=VERIFY %s
 
+; Now try the same with split dwarf.
+; RUN: %llc_dwarf -split-dwarf-file=foo.dwo -accel-tables=Dwarf -filetype=obj -o %t < %s
+; RUN: llvm-dwarfdump -debug-names %t | FileCheck %s
+
 ; Check the header
 ; CHECK: CU count: 1
 ; CHECK: Local TU count: 0
 ; CHECK: Foreign TU count: 0
 ; CHECK: Name count: 1
 ; CHECK: CU[0]: 0x{{[0-9a-f]*}}
 
 ; CHECK: Abbreviation [[ABBREV:0x[0-9a-f]*]]