DebugInfo: Don't allow type units to references types in the CU

We could only do this in limited ways (since we emit the TUs first, we
can't use ref_addr (& we can't use that in Split DWARF either) - so we
had to synthesize declarations into the TUs) and they were ambiguous in
some cases (if the CU type had internal linkage, parsing the TU would
require knowing which CU was referencing the TU to know which type the
declaration was for, which seems not-ideal). So to avoid all that, let's
just not reference types defined in the CU from TUs - instead moving the
TU type into the CU (recursively).

This does increase debug info size (by pulling more things out of type
units, into the compile unit) - about 2% of uncompressed dwp file size
for clang -O0 -g -gsplit-dwarf. (5% .debug_info.dwo section size
increase in the .dwp)

Author: dwblaikie

cross-project-tests/debuginfo-tests/clang_llvm_roundtrip/simplified_template_names.cpp

@@ -333,3 +333,21 @@ void t8::mem() {
   f1<t7>();
   f1<decltype(&t8::mem)>();
 }
+namespace complex_type_units {
+void external_function();
+namespace {
+struct internal_type;
+}
+template <void (*)() = external_function> struct t2;
+template <typename = t2<>> class t3 {};
+template <typename = internal_type, typename = t3<>>
+struct t4 {
+};
+struct t5 {
+    t4<> v1;
+};
+void f1() {
+  t5 v1;
+  t3<> v2;
+}
+}

llvm/lib/CodeGen/AsmPrinter/AddressPool.cpp

@@ -17,7 +17,7 @@
 using namespace llvm;
 
 unsigned AddressPool::getIndex(const MCSymbol *Sym, bool TLS) {
-  HasBeenUsed = true;
+  resetUsedFlag(true);
   auto IterBool =
       Pool.insert(std::make_pair(Sym, AddressPoolEntry(Pool.size(), TLS)));
   return IterBool.first->second.Number;

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -3444,22 +3444,6 @@ void DwarfDebug::addDwarfTypeUnitType(DwarfCompileUnit &CU,
   CU.addDIETypeSignature(RefDie, Signature);
 }
 
-DwarfDebug::NonTypeUnitContext::NonTypeUnitContext(DwarfDebug *DD)
-    : DD(DD),
-      TypeUnitsUnderConstruction(std::move(DD->TypeUnitsUnderConstruction)), AddrPoolUsed(DD->AddrPool.hasBeenUsed()) {
-  DD->TypeUnitsUnderConstruction.clear();
-  DD->AddrPool.resetUsedFlag();
-}
-
-DwarfDebug::NonTypeUnitContext::~NonTypeUnitContext() {
-  DD->TypeUnitsUnderConstruction = std::move(TypeUnitsUnderConstruction);
-  DD->AddrPool.resetUsedFlag(AddrPoolUsed);
-}
-
-DwarfDebug::NonTypeUnitContext DwarfDebug::enterNonTypeUnitContext() {
-  return NonTypeUnitContext(this);
-}
-
 // Add the Name along with its companion DIE to the appropriate accelerator
 // table (for AccelTableKind::Dwarf it's always AccelDebugNames, for
 // AccelTableKind::Apple, we use the table we got as an argument). If

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h

@@ -665,19 +665,6 @@ class DwarfDebug : public DebugHandlerBase {
   void addDwarfTypeUnitType(DwarfCompileUnit &CU, StringRef Identifier,
                             DIE &Die, const DICompositeType *CTy);
 
-  class NonTypeUnitContext {
-    DwarfDebug *DD;
-    decltype(DwarfDebug::TypeUnitsUnderConstruction) TypeUnitsUnderConstruction;
-    bool AddrPoolUsed;
-    friend class DwarfDebug;
-    NonTypeUnitContext(DwarfDebug *DD);
-  public:
-    NonTypeUnitContext(NonTypeUnitContext&&) = default;
-    ~NonTypeUnitContext();
-  };
-
-  NonTypeUnitContext enterNonTypeUnitContext();
-
   /// Add a label so that arange data can be generated for it.
   void addArangeLabel(SymbolCU SCU) { ArangeLabels.push_back(SCU); }
 

llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp

@@ -592,10 +592,8 @@ DIE *DwarfUnit::createTypeDIE(const DIScope *Context, DIE &ContextDIE,
       // Skip updating the accelerator tables since this is not the full type.
       if (MDString *TypeId = CTy->getRawIdentifier())
         DD->addDwarfTypeUnitType(getCU(), TypeId->getString(), TyDIE, CTy);
-      else {
-        auto X = DD->enterNonTypeUnitContext();
+      else
         finishNonUnitTypeDIE(TyDIE, CTy);
-      }
       return &TyDIE;
     }
     constructTypeDIE(TyDIE, CTy);
@@ -1843,11 +1841,5 @@ void DwarfUnit::addRnglistsBase() {
 }
 
 void DwarfTypeUnit::finishNonUnitTypeDIE(DIE& D, const DICompositeType *CTy) {
-  addFlag(D, dwarf::DW_AT_declaration);
-  StringRef Name = CTy->getName();
-  if (!Name.empty())
-    addString(D, dwarf::DW_AT_name, Name);
-  if (Name.startswith("_STN") || !Name.contains('<'))
-    addTemplateParams(D, CTy->getTemplateParams());
-  getCU().createTypeDIE(CTy);
+  DD->getAddressPool().resetUsedFlag(true);
 }

llvm/test/DebugInfo/X86/addr-tu-to-non-tu.ll

@@ -40,14 +40,14 @@
 ; CHECK:   DW_AT_name ("t3")
 ; CHECK:   DW_TAG_member
 ; CHECK:     DW_AT_type {{.*}} "t2<&foo>"
-; CHECK: DW_TAG_namespace
-; CHECK: [[T1:0x[0-9a-f]*]]:  DW_TAG_structure_type
-; CHECK:     DW_AT_name    ("t1")
 ; CHECK: DW_TAG_structure_type
 ; CHECK:   DW_AT_name ("t2<&foo>")
 ; CHECK:   DW_TAG_member
 ; CHECK:     DW_AT_name    ("v1")
-; CHECK:     DW_AT_type    ([[T1]] "(anonymous namespace)::t1")
+; CHECK:     DW_AT_type    ([[T1:0x[0-9a-f]*]] "(anonymous namespace)::t1")
+; CHECK: DW_TAG_namespace
+; CHECK: [[T1]]:  DW_TAG_structure_type
+; CHECK:     DW_AT_name    ("t1")
 
 ; CHECK: .debug_types contents: