[DebugInfo] Add a specification attribute to LLVM DebugInfo (#115362)

Add a specification attribute to LLVM DebugInfo, which is analogous
to DWARF's DW_AT_specification. According to the DWARF spec:
"A debugging information entry that represents a declaration that
completes another (earlier) non-defining declaration may have a
DW_AT_specification attribute whose value is a reference to the
debugging information entry representing the non-defining declaration."

This patch allows types to be specifications of other types. This is
used by Swift to represent generic types. For example, given this Swift
program:

```
struct MyStruct<T> {
    let t: T
}

let variable = MyStruct<Int>(t: 43)
```

The Swift compiler emits (roughly) an unsubtituted type for MyStruct<T>:
```
DW_TAG_structure_type
    DW_AT_name	("MyStruct")
    // "$s1w8MyStructVyxGD" is a Swift mangled name roughly equivalent to 
    // MyStruct<T>
    DW_AT_linkage_name	("$s1w8MyStructVyxGD")
    // other attributes here
```
And a specification for MyStruct<Int>:
```
DW_TAG_structure_type
    DW_AT_specification	(<link to "MyStruct">)
    // "$s1w8MyStructVySiGD" is a Swift mangled name equivalent to
    // MyStruct<Int>
    DW_AT_linkage_name	("$s1w8MyStructVySiGD")
    DW_AT_byte_size	(0x08)
    // other attributes here
```

llvm/include/llvm/IR/DIBuilder.h

@@ -488,6 +488,8 @@ namespace llvm {
     /// \param Elements     Struct elements.
     /// \param RunTimeLang  Optional parameter, Objective-C runtime version.
     /// \param UniqueIdentifier A unique identifier for the struct.
+    /// \param Specification The type that this type completes. This is used by
+    /// Swift to represent generic types.
     /// \param NumExtraInhabitants The number of extra inhabitants of the type.
     /// An extra inhabitant is a bit pattern that does not represent a valid
     /// value for instances of a given type. This is used by the Swift language.
@@ -496,7 +498,7 @@ namespace llvm {
         uint64_t SizeInBits, uint32_t AlignInBits, DINode::DIFlags Flags,
         DIType *DerivedFrom, DINodeArray Elements, unsigned RunTimeLang = 0,
         DIType *VTableHolder = nullptr, StringRef UniqueIdentifier = "",
-        uint32_t NumExtraInhabitants = 0);
+        DIType *Specification = nullptr, uint32_t NumExtraInhabitants = 0);
 
     /// Create debugging information entry for an union.
     /// \param Scope        Scope in which this union is defined.

llvm/include/llvm/IR/DebugInfoMetadata.h

@@ -1201,7 +1201,7 @@ class DICompositeType : public DIType {
   static DICompositeType *
   getImpl(LLVMContext &Context, unsigned Tag, StringRef Name, Metadata *File,
           unsigned Line, DIScope *Scope, DIType *BaseType, uint64_t SizeInBits,
-          uint32_t AlignInBits, uint64_t OffsetInBits,
+          uint32_t AlignInBits, uint64_t OffsetInBits, DIType *Specification,
           uint32_t NumExtraInhabitants, DIFlags Flags, DINodeArray Elements,
           unsigned RuntimeLang, DIType *VTableHolder,
           DITemplateParameterArray TemplateParams, StringRef Identifier,
@@ -1215,7 +1215,7 @@ class DICompositeType : public DIType {
                    TemplateParams.get(),
                    getCanonicalMDString(Context, Identifier), Discriminator,
                    DataLocation, Associated, Allocated, Rank, Annotations.get(),
-                   NumExtraInhabitants, Storage, ShouldCreate);
+                   Specification, NumExtraInhabitants, Storage, ShouldCreate);
   }
   static DICompositeType *
   getImpl(LLVMContext &Context, unsigned Tag, MDString *Name, Metadata *File,
@@ -1225,8 +1225,9 @@ class DICompositeType : public DIType {
           Metadata *VTableHolder, Metadata *TemplateParams,
           MDString *Identifier, Metadata *Discriminator, Metadata *DataLocation,
           Metadata *Associated, Metadata *Allocated, Metadata *Rank,
-          Metadata *Annotations, uint32_t NumExtraInhabitants,
-          StorageType Storage, bool ShouldCreate = true);
+          Metadata *Annotations, Metadata *Specification,
+          uint32_t NumExtraInhabitants, StorageType Storage,
+          bool ShouldCreate = true);
 
   TempDICompositeType cloneImpl() const {
     return getTemporary(
@@ -1235,7 +1236,8 @@ class DICompositeType : public DIType {
         getFlags(), getElements(), getRuntimeLang(), getVTableHolder(),
         getTemplateParams(), getIdentifier(), getDiscriminator(),
         getRawDataLocation(), getRawAssociated(), getRawAllocated(),
-        getRawRank(), getAnnotations(), getNumExtraInhabitants());
+        getRawRank(), getAnnotations(), getSpecification(),
+        getNumExtraInhabitants());
   }
 
 public:
@@ -1249,11 +1251,12 @@ class DICompositeType : public DIType {
        StringRef Identifier = "", DIDerivedType *Discriminator = nullptr,
        Metadata *DataLocation = nullptr, Metadata *Associated = nullptr,
        Metadata *Allocated = nullptr, Metadata *Rank = nullptr,
-       DINodeArray Annotations = nullptr, uint32_t NumExtraInhabitants = 0),
+       DINodeArray Annotations = nullptr, DIType *Specification = nullptr,
+       uint32_t NumExtraInhabitants = 0),
       (Tag, Name, File, Line, Scope, BaseType, SizeInBits, AlignInBits,
-       OffsetInBits, NumExtraInhabitants, Flags, Elements, RuntimeLang,
-       VTableHolder, TemplateParams, Identifier, Discriminator, DataLocation,
-       Associated, Allocated, Rank, Annotations))
+       OffsetInBits, Specification, NumExtraInhabitants, Flags, Elements,
+       RuntimeLang, VTableHolder, TemplateParams, Identifier, Discriminator,
+       DataLocation, Associated, Allocated, Rank, Annotations))
   DEFINE_MDNODE_GET(
       DICompositeType,
       (unsigned Tag, MDString *Name, Metadata *File, unsigned Line,
@@ -1264,11 +1267,11 @@ class DICompositeType : public DIType {
        Metadata *Discriminator = nullptr, Metadata *DataLocation = nullptr,
        Metadata *Associated = nullptr, Metadata *Allocated = nullptr,
        Metadata *Rank = nullptr, Metadata *Annotations = nullptr,
-       uint32_t NumExtraInhabitants = 0),
+       Metadata *Specification = nullptr, uint32_t NumExtraInhabitants = 0),
       (Tag, Name, File, Line, Scope, BaseType, SizeInBits, AlignInBits,
        OffsetInBits, Flags, Elements, RuntimeLang, VTableHolder, TemplateParams,
        Identifier, Discriminator, DataLocation, Associated, Allocated, Rank,
-       Annotations, NumExtraInhabitants))
+       Annotations, Specification, NumExtraInhabitants))
 
   TempDICompositeType clone() const { return cloneImpl(); }
 
@@ -1283,8 +1286,9 @@ class DICompositeType : public DIType {
   getODRType(LLVMContext &Context, MDString &Identifier, unsigned Tag,
              MDString *Name, Metadata *File, unsigned Line, Metadata *Scope,
              Metadata *BaseType, uint64_t SizeInBits, uint32_t AlignInBits,
-             uint64_t OffsetInBits, uint32_t NumExtraInhabitants, DIFlags Flags,
-             Metadata *Elements, unsigned RuntimeLang, Metadata *VTableHolder,
+             uint64_t OffsetInBits, Metadata *Specification,
+             uint32_t NumExtraInhabitants, DIFlags Flags, Metadata *Elements,
+             unsigned RuntimeLang, Metadata *VTableHolder,
              Metadata *TemplateParams, Metadata *Discriminator,
              Metadata *DataLocation, Metadata *Associated, Metadata *Allocated,
              Metadata *Rank, Metadata *Annotations);
@@ -1300,14 +1304,16 @@ class DICompositeType : public DIType {
   ///
   /// If not \a LLVMContext::isODRUniquingDebugTypes(), this function returns
   /// nullptr.
-  static DICompositeType *buildODRType(
-      LLVMContext &Context, MDString &Identifier, unsigned Tag, MDString *Name,
-      Metadata *File, unsigned Line, Metadata *Scope, Metadata *BaseType,
-      uint64_t SizeInBits, uint32_t AlignInBits, uint64_t OffsetInBits,
-      uint32_t NumExtraInhabitants, DIFlags Flags, Metadata *Elements,
-      unsigned RuntimeLang, Metadata *VTableHolder, Metadata *TemplateParams,
-      Metadata *Discriminator, Metadata *DataLocation, Metadata *Associated,
-      Metadata *Allocated, Metadata *Rank, Metadata *Annotations);
+  static DICompositeType *
+  buildODRType(LLVMContext &Context, MDString &Identifier, unsigned Tag,
+               MDString *Name, Metadata *File, unsigned Line, Metadata *Scope,
+               Metadata *BaseType, uint64_t SizeInBits, uint32_t AlignInBits,
+               uint64_t OffsetInBits, Metadata *Specification,
+               uint32_t NumExtraInhabitants, DIFlags Flags, Metadata *Elements,
+               unsigned RuntimeLang, Metadata *VTableHolder,
+               Metadata *TemplateParams, Metadata *Discriminator,
+               Metadata *DataLocation, Metadata *Associated,
+               Metadata *Allocated, Metadata *Rank, Metadata *Annotations);
 
   DIType *getBaseType() const { return cast_or_null<DIType>(getRawBaseType()); }
   DINodeArray getElements() const {
@@ -1367,6 +1373,10 @@ class DICompositeType : public DIType {
     return cast_or_null<MDTuple>(getRawAnnotations());
   }
 
+  Metadata *getRawSpecification() const { return getOperand(14); }
+  DIType *getSpecification() const {
+    return cast_or_null<DIType>(getRawSpecification());
+  }
   /// Replace operands.
   ///
   /// If this \a isUniqued() and not \a isResolved(), on a uniquing collision

llvm/lib/AsmParser/LLParser.cpp

@@ -5437,7 +5437,8 @@ bool LLParser::parseDICompositeType(MDNode *&Result, bool IsDistinct) {
   OPTIONAL(allocated, MDField, );                                              \
   OPTIONAL(rank, MDSignedOrMDField, );                                         \
   OPTIONAL(annotations, MDField, );                                            \
-  OPTIONAL(num_extra_inhabitants, MDUnsignedField, (0, UINT32_MAX));
+  OPTIONAL(num_extra_inhabitants, MDUnsignedField, (0, UINT32_MAX));           \
+  OPTIONAL(specification, MDField, );
   PARSE_MD_FIELDS();
 #undef VISIT_MD_FIELDS
 
@@ -5453,10 +5454,10 @@ bool LLParser::parseDICompositeType(MDNode *&Result, bool IsDistinct) {
     if (auto *CT = DICompositeType::buildODRType(
             Context, *identifier.Val, tag.Val, name.Val, file.Val, line.Val,
             scope.Val, baseType.Val, size.Val, align.Val, offset.Val,
-            num_extra_inhabitants.Val, flags.Val, elements.Val, runtimeLang.Val,
-            vtableHolder.Val, templateParams.Val, discriminator.Val,
-            dataLocation.Val, associated.Val, allocated.Val, Rank,
-            annotations.Val)) {
+            specification.Val, num_extra_inhabitants.Val, flags.Val,
+            elements.Val, runtimeLang.Val, vtableHolder.Val, templateParams.Val,
+            discriminator.Val, dataLocation.Val, associated.Val, allocated.Val,
+            Rank, annotations.Val)) {
       Result = CT;
       return false;
     }
@@ -5469,7 +5470,7 @@ bool LLParser::parseDICompositeType(MDNode *&Result, bool IsDistinct) {
        size.Val, align.Val, offset.Val, flags.Val, elements.Val,
        runtimeLang.Val, vtableHolder.Val, templateParams.Val, identifier.Val,
        discriminator.Val, dataLocation.Val, associated.Val, allocated.Val, Rank,
-       annotations.Val, num_extra_inhabitants.Val));
+       annotations.Val, specification.Val, num_extra_inhabitants.Val));
   return false;
 }
 

llvm/lib/Bitcode/Reader/MetadataLoader.cpp

@@ -1600,7 +1600,7 @@ Error MetadataLoader::MetadataLoaderImpl::parseOneMetadata(
     break;
   }
   case bitc::METADATA_COMPOSITE_TYPE: {
-    if (Record.size() < 16 || Record.size() > 23)
+    if (Record.size() < 16 || Record.size() > 24)
       return error("Invalid record");
 
     // If we have a UUID and this is not a forward declaration, lookup the
@@ -1630,6 +1630,7 @@ Error MetadataLoader::MetadataLoaderImpl::parseOneMetadata(
     Metadata *Allocated = nullptr;
     Metadata *Rank = nullptr;
     Metadata *Annotations = nullptr;
+    Metadata *Specification = nullptr;
     auto *Identifier = getMDString(Record[15]);
     // If this module is being parsed so that it can be ThinLTO imported
     // into another module, composite types only need to be imported as
@@ -1678,14 +1679,18 @@ Error MetadataLoader::MetadataLoaderImpl::parseOneMetadata(
       if (Record.size() > 21) {
         Annotations = getMDOrNull(Record[21]);
       }
+      if (Record.size() > 23) {
+        Specification = getMDOrNull(Record[23]);
+      }
     }
     DICompositeType *CT = nullptr;
     if (Identifier)
       CT = DICompositeType::buildODRType(
           Context, *Identifier, Tag, Name, File, Line, Scope, BaseType,
-          SizeInBits, AlignInBits, OffsetInBits, NumExtraInhabitants, Flags,
-          Elements, RuntimeLang, VTableHolder, TemplateParams, Discriminator,
-          DataLocation, Associated, Allocated, Rank, Annotations);
+          SizeInBits, AlignInBits, OffsetInBits, Specification,
+          NumExtraInhabitants, Flags, Elements, RuntimeLang, VTableHolder,
+          TemplateParams, Discriminator, DataLocation, Associated, Allocated,
+          Rank, Annotations);
 
     // Create a node if we didn't get a lazy ODR type.
     if (!CT)
@@ -1694,7 +1699,8 @@ Error MetadataLoader::MetadataLoaderImpl::parseOneMetadata(
                             SizeInBits, AlignInBits, OffsetInBits, Flags,
                             Elements, RuntimeLang, VTableHolder, TemplateParams,
                             Identifier, Discriminator, DataLocation, Associated,
-                            Allocated, Rank, Annotations, NumExtraInhabitants));
+                            Allocated, Rank, Annotations, Specification,
+                            NumExtraInhabitants));
     if (!IsNotUsedInTypeRef && Identifier)
       MetadataList.addTypeRef(*Identifier, *cast<DICompositeType>(CT));
 

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -1947,6 +1947,7 @@ void ModuleBitcodeWriter::writeDICompositeType(
   Record.push_back(VE.getMetadataOrNullID(N->getRawRank()));
   Record.push_back(VE.getMetadataOrNullID(N->getAnnotations().get()));
   Record.push_back(N->getNumExtraInhabitants());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawSpecification()));
 
   Stream.EmitRecord(bitc::METADATA_COMPOSITE_TYPE, Record, Abbrev);
   Record.clear();

llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp

@@ -1043,6 +1043,11 @@ void DwarfUnit::constructTypeDIE(DIE &Buffer, const DICompositeType *CTy) {
         addUInt(Buffer, dwarf::DW_AT_calling_convention, dwarf::DW_FORM_data1,
                 CC);
     }
+
+    if (auto *SpecifiedFrom = CTy->getSpecification())
+      addDIEEntry(Buffer, dwarf::DW_AT_specification,
+                  *getOrCreateContextDIE(SpecifiedFrom));
+
     break;
   }
   default:

llvm/lib/IR/AsmWriter.cpp

@@ -2235,6 +2235,8 @@ static void writeDICompositeType(raw_ostream &Out, const DICompositeType *N,
   else
     Printer.printMetadata("rank", N->getRawRank(), /*ShouldSkipNull */ true);
   Printer.printMetadata("annotations", N->getRawAnnotations());
+  if (auto *Specification = N->getRawSpecification())
+    Printer.printMetadata("specification", Specification);
   Out << ")";
 }
 

llvm/lib/IR/DIBuilder.cpp

@@ -521,13 +521,13 @@ DICompositeType *DIBuilder::createStructType(
     DIScope *Context, StringRef Name, DIFile *File, unsigned LineNumber,
     uint64_t SizeInBits, uint32_t AlignInBits, DINode::DIFlags Flags,
     DIType *DerivedFrom, DINodeArray Elements, unsigned RunTimeLang,
-    DIType *VTableHolder, StringRef UniqueIdentifier,
+    DIType *VTableHolder, StringRef UniqueIdentifier, DIType *Specification,
     uint32_t NumExtraInhabitants) {
   auto *R = DICompositeType::get(
       VMContext, dwarf::DW_TAG_structure_type, Name, File, LineNumber,
       getNonCompileUnitScope(Context), DerivedFrom, SizeInBits, AlignInBits, 0,
       Flags, Elements, RunTimeLang, VTableHolder, nullptr, UniqueIdentifier,
-      nullptr, nullptr, nullptr, nullptr, nullptr, nullptr,
+      nullptr, nullptr, nullptr, nullptr, nullptr, nullptr, Specification,
       NumExtraInhabitants);
   trackIfUnresolved(R);
   return R;

llvm/lib/IR/DebugInfoMetadata.cpp

@@ -770,21 +770,21 @@ DICompositeType *DICompositeType::getImpl(
     Metadata *Elements, unsigned RuntimeLang, Metadata *VTableHolder,
     Metadata *TemplateParams, MDString *Identifier, Metadata *Discriminator,
     Metadata *DataLocation, Metadata *Associated, Metadata *Allocated,
-    Metadata *Rank, Metadata *Annotations, uint32_t NumExtraInhabitants,
-    StorageType Storage, bool ShouldCreate) {
+    Metadata *Rank, Metadata *Annotations, Metadata *Specification,
+    uint32_t NumExtraInhabitants, StorageType Storage, bool ShouldCreate) {
   assert(isCanonical(Name) && "Expected canonical MDString");
 
   // Keep this in sync with buildODRType.
-  DEFINE_GETIMPL_LOOKUP(DICompositeType,
-                        (Tag, Name, File, Line, Scope, BaseType, SizeInBits,
-                         AlignInBits, OffsetInBits, Flags, Elements,
-                         RuntimeLang, VTableHolder, TemplateParams, Identifier,
-                         Discriminator, DataLocation, Associated, Allocated,
-                         Rank, Annotations, NumExtraInhabitants));
+  DEFINE_GETIMPL_LOOKUP(
+      DICompositeType,
+      (Tag, Name, File, Line, Scope, BaseType, SizeInBits, AlignInBits,
+       OffsetInBits, Flags, Elements, RuntimeLang, VTableHolder, TemplateParams,
+       Identifier, Discriminator, DataLocation, Associated, Allocated, Rank,
+       Annotations, Specification, NumExtraInhabitants));
   Metadata *Ops[] = {File,          Scope,        Name,           BaseType,
                      Elements,      VTableHolder, TemplateParams, Identifier,
                      Discriminator, DataLocation, Associated,     Allocated,
-                     Rank,          Annotations};
+                     Rank,          Annotations,  Specification};
   DEFINE_GETIMPL_STORE(DICompositeType,
                        (Tag, Line, RuntimeLang, SizeInBits, AlignInBits,
                         OffsetInBits, NumExtraInhabitants, Flags),
@@ -795,10 +795,11 @@ DICompositeType *DICompositeType::buildODRType(
     LLVMContext &Context, MDString &Identifier, unsigned Tag, MDString *Name,
     Metadata *File, unsigned Line, Metadata *Scope, Metadata *BaseType,
     uint64_t SizeInBits, uint32_t AlignInBits, uint64_t OffsetInBits,
-    uint32_t NumExtraInhabitants, DIFlags Flags, Metadata *Elements,
-    unsigned RuntimeLang, Metadata *VTableHolder, Metadata *TemplateParams,
-    Metadata *Discriminator, Metadata *DataLocation, Metadata *Associated,
-    Metadata *Allocated, Metadata *Rank, Metadata *Annotations) {
+    Metadata *Specification, uint32_t NumExtraInhabitants, DIFlags Flags,
+    Metadata *Elements, unsigned RuntimeLang, Metadata *VTableHolder,
+    Metadata *TemplateParams, Metadata *Discriminator, Metadata *DataLocation,
+    Metadata *Associated, Metadata *Allocated, Metadata *Rank,
+    Metadata *Annotations) {
   assert(!Identifier.getString().empty() && "Expected valid identifier");
   if (!Context.isODRUniquingDebugTypes())
     return nullptr;
@@ -809,8 +810,7 @@ DICompositeType *DICompositeType::buildODRType(
                AlignInBits, OffsetInBits, Flags, Elements, RuntimeLang,
                VTableHolder, TemplateParams, &Identifier, Discriminator,
                DataLocation, Associated, Allocated, Rank, Annotations,
-               NumExtraInhabitants);
-
+               Specification, NumExtraInhabitants);
   if (CT->getTag() != Tag)
     return nullptr;
 
@@ -825,7 +825,7 @@ DICompositeType *DICompositeType::buildODRType(
   Metadata *Ops[] = {File,          Scope,        Name,           BaseType,
                      Elements,      VTableHolder, TemplateParams, &Identifier,
                      Discriminator, DataLocation, Associated,     Allocated,
-                     Rank,          Annotations};
+                     Rank,          Annotations,  Specification};
   assert((std::end(Ops) - std::begin(Ops)) == (int)CT->getNumOperands() &&
          "Mismatched number of operands");
   for (unsigned I = 0, E = CT->getNumOperands(); I != E; ++I)
@@ -838,10 +838,11 @@ DICompositeType *DICompositeType::getODRType(
     LLVMContext &Context, MDString &Identifier, unsigned Tag, MDString *Name,
     Metadata *File, unsigned Line, Metadata *Scope, Metadata *BaseType,
     uint64_t SizeInBits, uint32_t AlignInBits, uint64_t OffsetInBits,
-    uint32_t NumExtraInhabitants, DIFlags Flags, Metadata *Elements,
-    unsigned RuntimeLang, Metadata *VTableHolder, Metadata *TemplateParams,
-    Metadata *Discriminator, Metadata *DataLocation, Metadata *Associated,
-    Metadata *Allocated, Metadata *Rank, Metadata *Annotations) {
+    Metadata *Specification, uint32_t NumExtraInhabitants, DIFlags Flags,
+    Metadata *Elements, unsigned RuntimeLang, Metadata *VTableHolder,
+    Metadata *TemplateParams, Metadata *Discriminator, Metadata *DataLocation,
+    Metadata *Associated, Metadata *Allocated, Metadata *Rank,
+    Metadata *Annotations) {
   assert(!Identifier.getString().empty() && "Expected valid identifier");
   if (!Context.isODRUniquingDebugTypes())
     return nullptr;
@@ -851,7 +852,7 @@ DICompositeType *DICompositeType::getODRType(
         Context, Tag, Name, File, Line, Scope, BaseType, SizeInBits,
         AlignInBits, OffsetInBits, Flags, Elements, RuntimeLang, VTableHolder,
         TemplateParams, &Identifier, Discriminator, DataLocation, Associated,
-        Allocated, Rank, Annotations, NumExtraInhabitants);
+        Allocated, Rank, Annotations, Specification, NumExtraInhabitants);
   } else {
     if (CT->getTag() != Tag)
       return nullptr;