4 files changed, 28 insertions, 3 deletions
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 7d03a3930d7..45875667027 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -467,7 +467,10 @@ void DwarfDebug::beginModule() {
     for (auto *Ty : CUNode->getRetainedTypes()) {
       // The retained types array by design contains pointers to
       // MDNodes rather than DIRefs. Unique them here.
-      CU.getOrCreateTypeDIE(cast<DIType>(resolve(Ty->getRef())));
+      DIType *RT = cast<DIType>(resolve(Ty->getRef()));
+      if (!RT->isExternalTypeRef())
+        // There is no point in force-emitting a forward declaration.
+        CU.getOrCreateTypeDIE(RT);
     }
     // Emit imported_modules last so that the relevant context is already
     // available.
@@ -1884,7 +1887,7 @@ MCDwarfDwoLineTable *DwarfDebug::getDwoLineTable(const DwarfCompileUnit &CU) {
   return &SplitTypeUnitFileTable;
 }
 
-static uint64_t makeTypeSignature(StringRef Identifier) {
+uint64_t DwarfDebug::makeTypeSignature(StringRef Identifier) {
   MD5 Hash;
   Hash.update(Identifier);
   // ... take the least significant 8 bytes and return those. Our MD5
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h
index 01f34c6eb81..36502225c29 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h
@@ -544,6 +544,9 @@ public:
   /// Process end of an instruction.
   void endInstruction() override;
 
+  /// Perform an MD5 checksum of \p Identifier and return the lower 64 bits.
+  static uint64_t makeTypeSignature(StringRef Identifier);
+
   /// Add a DIE to the set of types that we're going to pull into
   /// type units.
   void addDwarfTypeUnitType(DwarfCompileUnit &CU, StringRef Identifier,
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
index 355582298e5..799398a8f2f 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
@@ -277,6 +277,13 @@ void DwarfUnit::addDIETypeSignature(DIE &Die, const DwarfTypeUnit &Type) {
                dwarf::DW_FORM_ref_sig8, DIETypeSignature(Type));
 }
 
+void DwarfUnit::addDIETypeSignature(DIE &Die, dwarf::Attribute Attribute,
+                                    StringRef Identifier) {
+  uint64_t Signature = DD->makeTypeSignature(Identifier);
+  Die.addValue(DIEValueAllocator, Attribute, dwarf::DW_FORM_ref_sig8,
+               DIEInteger(Signature));
+}
+
 void DwarfUnit::addDIEEntry(DIE &Die, dwarf::Attribute Attribute,
                             DIEEntry Entry) {
   const DIE *DieCU = Die.getUnitOrNull();
@@ -700,7 +707,8 @@ DIE *DwarfUnit::createTypeDIE(const DICompositeType *Ty) {
 
   constructTypeDIE(TyDIE, cast<DICompositeType>(Ty));
 
-  updateAcceleratorTables(Context, Ty, TyDIE);
+  if (!Ty->isExternalTypeRef())
+    updateAcceleratorTables(Context, Ty, TyDIE);
   return &TyDIE;
 }
 
@@ -899,6 +907,13 @@ void DwarfUnit::constructTypeDIE(DIE &Buffer, const DISubroutineType *CTy) {
 }
 
 void DwarfUnit::constructTypeDIE(DIE &Buffer, const DICompositeType *CTy) {
+  if (CTy->isExternalTypeRef()) {
+    StringRef Identifier = CTy->getIdentifier();
+    assert(!Identifier.empty() && "external type ref without identifier");
+    addFlag(Buffer, dwarf::DW_AT_declaration);
+    return addDIETypeSignature(Buffer, dwarf::DW_AT_signature, Identifier);
+  }
+
   // Add name if not anonymous or intermediate type.
   StringRef Name = CTy->getName();
 
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.h b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.h
index 44d9d2245dd..28fb71cc462 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.h
@@ -228,7 +228,11 @@ public:
   /// Add a DIE attribute data and value.
   void addDIEEntry(DIE &Die, dwarf::Attribute Attribute, DIEEntry Entry);
 
+  /// Add a type's DW_AT_signature and set the  declaration flag.
   void addDIETypeSignature(DIE &Die, const DwarfTypeUnit &Type);
+  /// Add an attribute containing the type signature for a unique identifier.
+  void addDIETypeSignature(DIE &Die, dwarf::Attribute Attribute,
+                           StringRef Identifier);
 
   /// Add block data.
   void addBlock(DIE &Die, dwarf::Attribute Attribute, DIELoc *Block);