[CodeView] Implement support for enums

[majnemer]

Summary

MSVC handles enums differently from structs and classes: a forward
declaration is not emitted unconditionally. MSVC does not emit an S_UDT
record for the enum.

[rnk]

lgtm

[aaboud]

lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

1095

Can you explain why we are lowering "Record Field List" instead of "Enumeration Field List"?
There is nothing in common between enum and class, is there?

I suggest to create a new function called lowerEnumerationFieldList().

lib/CodeGen/AsmPrinter/CodeViewDebug.h

class LLVM_LIBRARY_VISIBILITY CodeViewDebug : public DebugHandlerBase {
   codeview::TypeIndex lowerType(const DIType *Ty);
   codeview::TypeIndex lowerTypeAlias(const DIDerivedType *Ty);
   codeview::TypeIndex lowerTypeArray(const DICompositeType *Ty);
   codeview::TypeIndex lowerTypeBasic(const DIBasicType *Ty);
   codeview::TypeIndex lowerTypePointer(const DIDerivedType *Ty);
   codeview::TypeIndex lowerTypeMemberPointer(const DIDerivedType *Ty);
   codeview::TypeIndex lowerTypeModifier(const DIDerivedType *Ty);
   codeview::TypeIndex lowerTypeFunction(const DISubroutineType *Ty);
+  codeview::TypeIndex lowerTypeEnum(const DICompositeType *Ty);
   codeview::TypeIndex lowerTypeClass(const DICompositeType *Ty);
   codeview::TypeIndex lowerTypeUnion(const DICompositeType *Ty);
 
   /// Symbol records should point to complete types, but type records should
   /// always point to incomplete types to avoid cycles in the type graph. Only
   /// use this entry point when generating symbol records. The complete and
   /// incomplete type indices only differ for record types. All other types use
   /// the same index.

lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

case dwarf::DW_TAG_rvalue_reference_type:
     return lowerTypePointer(cast<DIDerivedType>(Ty));
   case dwarf::DW_TAG_ptr_to_member_type:
     return lowerTypeMemberPointer(cast<DIDerivedType>(Ty));
   case dwarf::DW_TAG_const_type:
   case dwarf::DW_TAG_volatile_type:
     return lowerTypeModifier(cast<DIDerivedType>(Ty));
   case dwarf::DW_TAG_subroutine_type:
     return lowerTypeFunction(cast<DISubroutineType>(Ty));
+  case dwarf::DW_TAG_enumeration_type:
+    return lowerTypeEnum(cast<DICompositeType>(Ty));
   case dwarf::DW_TAG_class_type:
   case dwarf::DW_TAG_structure_type:
     return lowerTypeClass(cast<DICompositeType>(Ty));
   case dwarf::DW_TAG_union_type:
     return lowerTypeUnion(cast<DICompositeType>(Ty));
   default:
     // Use the null type index.
     return TypeIndex();

 static ClassOptions getRecordUniqueNameOption(const DICompositeType *Ty) {
   // MSVC always sets this flag now, even for local types. Clang doesn't always
   // appear to give every type a linkage name, which may be problematic for us.
   // FIXME: Investigate the consequences of not following them here.
   return !Ty->getIdentifier().empty() ? ClassOptions::HasUniqueName
                                       : ClassOptions::None;
 }
 
+TypeIndex CodeViewDebug::lowerTypeEnum(const DICompositeType *Ty) {
+  ClassOptions CO = ClassOptions::None | getRecordUniqueNameOption(Ty);
+  TypeIndex FTI;
+  unsigned FieldCount = 0;
+
+  if (Ty->isForwardDecl())
+    CO |= ClassOptions::ForwardReference;
+  else
+    std::tie(FTI, FieldCount) = lowerRecordFieldList(Ty);
+
+  return TypeTable.writeEnum(EnumRecord(FieldCount, CO, FTI, Ty->getName(),
+                                        Ty->getIdentifier(),
+                                        getTypeIndex(Ty->getBaseType())));
+}
+
 TypeIndex CodeViewDebug::lowerTypeClass(const DICompositeType *Ty) {
   // First, construct the forward decl.  Don't look into Ty to compute the
   // forward decl options, since it might not be available in all TUs.
   TypeRecordKind Kind = getRecordKind(Ty);
   ClassOptions CO =
       ClassOptions::ForwardReference | getRecordUniqueNameOption(Ty);
   TypeIndex FwdDeclTI = TypeTable.writeClass(ClassRecord(
       Kind, 0, CO, HfaKind::None, WindowsRTClassKind::None, TypeIndex(),
if (auto *SP = dyn_cast<DISubprogram>(Element)) {
           MemberCount++;
         }
       } else if (Member->getTag() == dwarf::DW_TAG_friend) {
         // Ignore friend members. It appears that MSVC emitted info about
         // friends in the past, but modern versions do not.
       }
       // FIXME: Get clang to emit nested types here and do something with
       // them.
+    } else if (auto *Enumerator = dyn_cast<DIEnumerator>(Element)) {
+      Fields.writeEnumerator(EnumeratorRecord(
+          MemberAccess::Public, APSInt::getUnsigned(Enumerator->getValue()),
+          Enumerator->getName()));
     }
     // Skip other unrecognized kinds of elements.
   }
   return {TypeTable.writeFieldList(Fields), MemberCount};
 }
 
 TypeIndex CodeViewDebug::getTypeIndex(DITypeRef TypeRef) {
   const DIType *Ty = TypeRef.resolve();

test/DebugInfo/COFF/enum.ll

+; RUN: llc < %s -filetype=obj | llvm-readobj - -codeview | FileCheck %s
+
+; Generated from the following C++ source:
+; enum E : int { BLAH };
+; E e;
+
+; CHECK:     CodeViewTypes [
+; CHECK:       UnknownLeaf (0x1000) {
+; CHECK-NEXT:    TypeLeafKind: LF_FIELDLIST (0x1203)
+; CHECK-NEXT:    Enumerator {
+; CHECK-NEXT:      AccessSpecifier: Public (0x3)
+; CHECK-NEXT:      EnumValue: 0
+; CHECK-NEXT:      Name: BLAH
+; CHECK-NEXT:    }
+; CHECK-NEXT:  }
+; CHECK-NEXT:  Enum (0x1001) {
+; CHECK-NEXT:    TypeLeafKind: LF_ENUM (0x1507)
+; CHECK-NEXT:    NumEnumerators: 0
+; CHECK-NEXT:    Properties [ (0x0)
+; CHECK-NEXT:    ]
+; CHECK-NEXT:    UnderlyingType: int (0x74)
+; CHECK-NEXT:    FieldListType: BLAH (0x1000)
+; CHECK-NEXT:    Name: E
+; CHECK-NEXT:  }
+
+target datalayout = "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32"
+target triple = "i686-pc-windows-msvc18.0.0"
+
+@"\01?e@@3W4E@@A" = global i32 0, align 4
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!10, !11}
+!llvm.ident = !{!12}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 3.9.0 (trunk 272790) (llvm/trunk 272813)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, globals: !8)
+!1 = !DIFile(filename: "-", directory: "/")
+!2 = !{!3}
+!3 = !DICompositeType(tag: DW_TAG_enumeration_type, name: "E", file: !4, line: 1, baseType: !5, size: 32, align: 32, elements: !6)
+!4 = !DIFile(filename: "<stdin>", directory: "/")
+!5 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
+!6 = !{!7}
+!7 = !DIEnumerator(name: "BLAH", value: 0)
+!8 = !{!9}
+!9 = distinct !DIGlobalVariable(name: "e", linkageName: "\01?e@@3W4E@@A", scope: !0, file: !4, line: 2, type: !3, isLocal: false, isDefinition: true, variable: i32* @"\01?e@@3W4E@@A")
+!10 = !{i32 2, !"CodeView", i32 1}
+!11 = !{i32 2, !"Debug Info Version", i32 3}
+!12 = !{!"clang version 3.9.0 (trunk 272790) (llvm/trunk 272813)"}