[CodeView] Don't generate dummy unnamed strcut/class/union type.

[zequanwu]

Summary

This aligns with MSVC's output.

Fix #57999

[rnk]

Since Clang creates the member list and only adds types for the benefit of codeview, should we change clang instead?

+@dblaikie

llvm/test/DebugInfo/COFF/nested-types.ll

214 ↗

(On Diff #476582)

So the test shows that we don't have NestedType records for unnamed unions & structs, right?

[dblaikie]

In D138326#3938128, @rnk wrote:

Since Clang creates the member list and only adds types for the benefit of codeview, should we change clang instead?

+@dblaikie

Looks like DWARF wants the types (in DWARF we describe the union and use the DWARF attribute DW_AT_export_symbols (encoded in the DICompositeType's DIFlagExportSymbols flag) to say that the names in the union are visible within the enclosing scope, but doesn't put an artificial name on those types. So probably the naming logic here https://github.com/llvm/llvm-project/blob/2e999b7dd1934a44d38c3a753460f1e5a217e9a5/clang/lib/CodeGen/CGDebugInfo.cpp#L336-L340 might be able to be removed - but I guess you probably still need it for non-nested unnamed types?

[zequanwu]

Reverted previous change and change clang side so that it doesn't emit nested anonymous record type when emitting code-view.

[zequanwu]

In D138326#3938128, @rnk wrote:

Since Clang creates the member list and only adds types for the benefit of codeview, should we change clang instead?

Yes, that's something clang does only for codeview, changed in clang side. It will still emit type info for unnamed records but not for anonymous records.

llvm/test/DebugInfo/COFF/nested-types.ll

214 ↗

(On Diff #476582)

Updated. We want NestedType records for unnamed unions & structs, but not for anonymous unions & structs. That's what MSVC does.

0x1004 | LF_FIELDLIST [size = 168]
           - LF_MEMBER [name = `i1`, Type = 0x0074 (int), offset = 0, attrs = public]
           - LF_NESTTYPE [name = `<unnamed-type-unnamed_union>`, parent = 0x1002]
           - LF_MEMBER [name = `unnamed_union`, Type = 0x1002, offset = 4, attrs = public]
           - LF_MEMBER [name = `i3`, Type = 0x0074 (int), offset = 8, attrs = public]
           - LF_NESTTYPE [name = `<unnamed-type-unnamed_struct>`, parent = 0x1003]
           - LF_MEMBER [name = `unnamed_struct`, Type = 0x1003, offset = 12, attrs = public]

[rnk]

Seems right to me, but I would prefer if someone else can review.

[zequanwu]

Landed at: https://reviews.llvm.org/rGbb5bcddcdbc151119f449be2d1e0d90f2e9c4258. Forgot to add the "Revision" line.

clang/lib/CodeGen/CGDebugInfo.cpp

for (const auto *I : record->decls())
         CollectRecordNormalField(field, layout.getFieldOffset(fieldNo), tunit,
                                  elements, RecordTy, record);
 
         // Bump field number for next field.
         ++fieldNo;
       } else if (CGM.getCodeGenOpts().EmitCodeView) {
         // Debug info for nested types is included in the member list only for
         // CodeView.
-        if (const auto *nestedType = dyn_cast<TypeDecl>(I))
+        if (const auto *nestedType = dyn_cast<TypeDecl>(I)) {
+          // MSVC doesn't generate nested type for anonymous struct/union.
+          if (isa<RecordDecl>(I) &&
+              cast<RecordDecl>(I)->isAnonymousStructOrUnion())
+            continue;
           if (!nestedType->isImplicit() &&
               nestedType->getDeclContext() == record)
             CollectRecordNestedType(nestedType, elements);
         }
       }
   }
+}
 
 llvm::DISubroutineType *
 CGDebugInfo::getOrCreateMethodType(const CXXMethodDecl *Method,
                                    llvm::DIFile *Unit) {
   const FunctionProtoType *Func = Method->getType()->getAs<FunctionProtoType>();
   if (Method->isStatic())
     return cast_or_null<llvm::DISubroutineType>(
         getOrCreateType(QualType(Func, 0), Unit));

clang/test/CodeGenCXX/debug-info-codeview-nested-types.cpp

 // RUN: %clang_cc1 %s -std=c++11 -triple=x86_64-pc-windows-msvc -debug-info-kind=limited -gcodeview -emit-llvm -o - | FileCheck %s
 
 struct HasNested {
   enum InnerEnum { _BUF_SIZE = 1 };
   typedef int InnerTypedef;
   enum { InnerEnumerator = 2 };
   struct InnerStruct { };
+
+  union { int i1; };
+  union { int i2; } unnamed_union;
+  struct { int i3; };
+  struct { int i4; } unnamed_struct;
 };
 HasNested f;
 
 // CHECK: ![[INNERENUM:[0-9]+]] = !DICompositeType(tag: DW_TAG_enumeration_type, name: "InnerEnum", {{.*}})
 // CHECK: ![[HASNESTED:[0-9]+]] = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "HasNested",
 // CHECK-SAME: elements: ![[MEMBERS:[0-9]+]],
 //
-// CHECK: ![[MEMBERS]] = !{![[INNERENUM]], ![[INNERTYPEDEF:[0-9]+]], ![[UNNAMEDENUM:[0-9]+]], ![[INNERSTRUCT:[0-9]+]]}
+// CHECK: ![[MEMBERS]] = !{![[INNERENUM]], ![[INNERTYPEDEF:[0-9]+]], ![[UNNAMEDENUM:[0-9]+]], ![[INNERSTRUCT:[0-9]+]], ![[ANONYMOUS_UNION:[0-9]+]], ![[UNNAMED_UNION_TYPE:[0-9]+]], ![[UNNAMED_UNION:[0-9]+]], ![[ANONYMOUS_STRUCT:[0-9]+]], ![[UNNAMED_STRUCT_TYPE:[0-9]+]], ![[UNNAMED_STRUCT:[0-9]+]]}
 //
 // CHECK: ![[INNERTYPEDEF]] = !DIDerivedType(tag: DW_TAG_typedef, name: "InnerTypedef", scope: ![[HASNESTED]]{{.*}})
 //
 // CHECK: ![[UNNAMEDENUM]] = !DICompositeType(tag: DW_TAG_enumeration_type, scope: ![[HASNESTED]],
 // CHECK-SAME: elements: ![[UNNAMEDMEMBERS:[0-9]+]],
 // CHECK: ![[UNNAMEDMEMBERS]] = !{![[INNERENUMERATOR:[0-9]+]]}
 // CHECK: ![[INNERENUMERATOR]] = !DIEnumerator(name: "InnerEnumerator", value: 2)
 //
 // CHECK: ![[INNERSTRUCT]] = !DICompositeType(tag: DW_TAG_structure_type, name: "InnerStruct"
 // CHECK-SAME: flags: DIFlagFwdDecl
+
+// CHECK: ![[ANONYMOUS_UNION]] = !DIDerivedType(tag: DW_TAG_member, 
+// CHECK-SAME: baseType: ![[ANONYMOUS_UNION_TYPE:[0-9]+]]
+// CHECK: ![[ANONYMOUS_UNION_TYPE]] = distinct !DICompositeType(tag: DW_TAG_union_type,
+// CHECK-SAME: elements: ![[ANONYMOUS_UNION_MEMBERS:[0-9]+]], identifier: ".?AT<unnamed-type-$S1>@HasNested@@")
+// CHECK: ![[ANONYMOUS_UNION_MEMBERS]] = !{![[ANONYMOUS_UNION_MEMBER:[0-9]+]]}
+// CHECK: ![[ANONYMOUS_UNION_MEMBER]] = !DIDerivedType(tag: DW_TAG_member, name: "i1"
+
+// CHECK: ![[UNNAMED_UNION_TYPE]] = distinct !DICompositeType(tag: DW_TAG_union_type, name: "<unnamed-type-unnamed_union>"
+// CHECK-SAME: elements: ![[UNNAMED_UNION_MEMBERS:[0-9]+]], identifier: ".?AT<unnamed-type-unnamed_union>@HasNested@@")
+// CHECK: ![[UNNAMED_UNION_MEMBERS]] = !{![[UNNAMED_UNION_MEMBER:[0-9]+]]}
+// CHECK: ![[UNNAMED_UNION_MEMBER]] = !DIDerivedType(tag: DW_TAG_member, name: "i2"
+// CHECK: ![[UNNAMED_UNION]] = !DIDerivedType(tag: DW_TAG_member, name: "unnamed_union"
+// CHECK-SAME: baseType: ![[UNNAMED_UNION_TYPE]]
+
+// CHECK: ![[ANONYMOUS_STRUCT]] = !DIDerivedType(tag: DW_TAG_member
+// CHECK-SAME: baseType: ![[ANONYMOUS_STRUCT_TYPE:[0-9]+]]
+// CHECK: ![[ANONYMOUS_STRUCT_TYPE]] = distinct !DICompositeType(tag: DW_TAG_structure_type
+// CHECK-SAME: elements: ![[ANONYMOUS_STRUCT_MEMBERS:[0-9]+]], identifier: ".?AU<unnamed-type-$S2>@HasNested@@")
+// CHECK: ![[ANONYMOUS_STRUCT_MEMBERS]] = !{![[ANONYMOUS_STRUCT_MEMBER:[0-9]+]]}
+// CHECK: ![[ANONYMOUS_STRUCT_MEMBER]] = !DIDerivedType(tag: DW_TAG_member, name: "i3"
+
+// CHECK: ![[UNNAMED_STRUCT_TYPE]] = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "<unnamed-type-unnamed_struct>"
+// CHECK-SAME: elements: ![[UNNAMED_STRUCT_MEMBERS:[0-9]+]], identifier: ".?AU<unnamed-type-unnamed_struct>@HasNested@@")
+// CHECK: ![[UNNAMED_STRUCT_MEMBERS]] = !{![[UNNAMED_STRUCT_MEMBER:[0-9]+]]}
+// CHECK: ![[UNNAMED_STRUCT_MEMBER]] = !DIDerivedType(tag: DW_TAG_member, name: "i4"
+// CHECK: ![[UNNAMED_STRUCT]] = !DIDerivedType(tag: DW_TAG_member, name: "unnamed_struct"
+// CHECK-SAME: baseType: ![[UNNAMED_STRUCT_TYPE]]
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