Reland "[llvm][DebugInfo] DWARFv5: static data members declarations are DW_TAG_variable (#72234)"

This was reverted because it broke the OCaml LLVM bindings.
Relanding the original patch but without changing the C-API.
They'll continue to work just fine as they do today. If in the
future there is a need to pass a new tag to the C-API for creating
static members, then we'll make the change to the OCaml bindings
at that time.

Original commit message:
"""
This patch adds the LLVM-side infrastructure to implement DWARFv5 issue
161118.1: "DW_TAG for C++ static data members".

The clang-side of this patch will simply construct the DIDerivedType
with a different DW_TAG.
"""

Author: Michael137

clang/lib/CodeGen/CGDebugInfo.cpp

@@ -1681,7 +1681,8 @@ CGDebugInfo::CreateRecordStaticField(const VarDecl *Var, llvm::DIType *RecordTy,
   llvm::DINode::DIFlags Flags = getAccessFlag(Var->getAccess(), RD);
   auto Align = getDeclAlignIfRequired(Var, CGM.getContext());
   llvm::DIDerivedType *GV = DBuilder.createStaticMemberType(
-      RecordTy, VName, VUnit, LineNumber, VTy, Flags, /* Val */ nullptr, Align);
+      RecordTy, VName, VUnit, LineNumber, VTy, Flags, /* Val */ nullptr,
+      llvm::dwarf::DW_TAG_member, Align);
   StaticDataMemberCache[Var->getCanonicalDecl()].reset(GV);
   StaticDataMemberDefinitionsToEmit.push_back(Var->getCanonicalDecl());
   return GV;

llvm/include/llvm/IR/DIBuilder.h

@@ -376,11 +376,12 @@ namespace llvm {
     /// \param Ty         Type of the static member.
     /// \param Flags      Flags to encode member attribute, e.g. private.
     /// \param Val        Const initializer of the member.
+    /// \param Tag        DWARF tag of the static member.
     /// \param AlignInBits  Member alignment.
     DIDerivedType *createStaticMemberType(DIScope *Scope, StringRef Name,
                                           DIFile *File, unsigned LineNo,
                                           DIType *Ty, DINode::DIFlags Flags,
-                                          Constant *Val,
+                                          Constant *Val, unsigned Tag,
                                           uint32_t AlignInBits = 0);
 
     /// Create debugging information entry for Objective-C

llvm/lib/IR/DIBuilder.cpp

@@ -405,12 +405,11 @@ DIDerivedType *
 DIBuilder::createStaticMemberType(DIScope *Scope, StringRef Name, DIFile *File,
                                   unsigned LineNumber, DIType *Ty,
                                   DINode::DIFlags Flags, llvm::Constant *Val,
-                                  uint32_t AlignInBits) {
+                                  unsigned Tag, uint32_t AlignInBits) {
   Flags |= DINode::FlagStaticMember;
-  return DIDerivedType::get(VMContext, dwarf::DW_TAG_member, Name, File,
-                            LineNumber, getNonCompileUnitScope(Scope), Ty, 0,
-                            AlignInBits, 0, std::nullopt, Flags,
-                            getConstantOrNull(Val));
+  return DIDerivedType::get(VMContext, Tag, Name, File, LineNumber,
+                            getNonCompileUnitScope(Scope), Ty, 0, AlignInBits,
+                            0, std::nullopt, Flags, getConstantOrNull(Val));
 }
 
 DIDerivedType *

llvm/lib/IR/DebugInfo.cpp

@@ -1315,17 +1315,15 @@ LLVMDIBuilderCreateUnspecifiedType(LLVMDIBuilderRef Builder, const char *Name,
   return wrap(unwrap(Builder)->createUnspecifiedType({Name, NameLen}));
 }
 
-LLVMMetadataRef
-LLVMDIBuilderCreateStaticMemberType(
+LLVMMetadataRef LLVMDIBuilderCreateStaticMemberType(
     LLVMDIBuilderRef Builder, LLVMMetadataRef Scope, const char *Name,
     size_t NameLen, LLVMMetadataRef File, unsigned LineNumber,
     LLVMMetadataRef Type, LLVMDIFlags Flags, LLVMValueRef ConstantVal,
     uint32_t AlignInBits) {
   return wrap(unwrap(Builder)->createStaticMemberType(
-                  unwrapDI<DIScope>(Scope), {Name, NameLen},
-                  unwrapDI<DIFile>(File), LineNumber, unwrapDI<DIType>(Type),
-                  map_from_llvmDIFlags(Flags), unwrap<Constant>(ConstantVal),
-                  AlignInBits));
+      unwrapDI<DIScope>(Scope), {Name, NameLen}, unwrapDI<DIFile>(File),
+      LineNumber, unwrapDI<DIType>(Type), map_from_llvmDIFlags(Flags),
+      unwrap<Constant>(ConstantVal), DW_TAG_member, AlignInBits));
 }
 
 LLVMMetadataRef

llvm/lib/IR/DebugInfoMetadata.cpp

@@ -711,7 +711,9 @@ Constant *DIDerivedType::getStorageOffsetInBits() const {
 }
 
 Constant *DIDerivedType::getConstant() const {
-  assert(getTag() == dwarf::DW_TAG_member && isStaticMember());
+  assert((getTag() == dwarf::DW_TAG_member ||
+          getTag() == dwarf::DW_TAG_variable) &&
+         isStaticMember());
   if (auto *C = cast_or_null<ConstantAsMetadata>(getExtraData()))
     return C->getValue();
   return nullptr;

llvm/lib/IR/Verifier.cpp

@@ -1172,6 +1172,7 @@ void Verifier::visitDIDerivedType(const DIDerivedType &N) {
               N.getTag() == dwarf::DW_TAG_restrict_type ||
               N.getTag() == dwarf::DW_TAG_atomic_type ||
               N.getTag() == dwarf::DW_TAG_member ||
+              (N.getTag() == dwarf::DW_TAG_variable && N.isStaticMember()) ||
               N.getTag() == dwarf::DW_TAG_inheritance ||
               N.getTag() == dwarf::DW_TAG_friend ||
               N.getTag() == dwarf::DW_TAG_set_type,

llvm/test/DebugInfo/Generic/dwarf5-debug-info-static-member.ll

@@ -0,0 +1,109 @@
+; RUN: %llc_dwarf -filetype=obj -o %t.o < %s
+; RUN: llvm-dwarfdump -v -debug-info %t.o | FileCheck %s -check-prefix=CHECK 
+
+; LLVM IR generated using: clang -emit-llvm -S -g -gdwarf-5
+;
+; struct C
+; {
+;   static int a;
+;   const static bool b = true;
+;   static constexpr int c = 15;
+; };
+; 
+; int C::a = 10;
+; 
+; int main()
+; {
+;   C instance_C;
+;   return C::a + (int)C::b + C::c;
+; }
+
+source_filename = "llvm/test/DebugInfo/X86/dwarf5-debug-info-static-member.ll"
+
+%struct.C = type { i8 }
+
+@_ZN1C1aE = global i32 10, align 4, !dbg !0
+
+; Function Attrs: mustprogress noinline norecurse nounwind optnone ssp uwtable(sync)
+define noundef i32 @main() #0 !dbg !26 {
+entry:
+  %retval = alloca i32, align 4
+  %instance_C = alloca %struct.C, align 1
+  store i32 0, ptr %retval, align 4
+  call void @llvm.dbg.declare(metadata ptr %instance_C, metadata !30, metadata !DIExpression()), !dbg !31
+  %0 = load i32, ptr @_ZN1C1aE, align 4, !dbg !32
+  %add = add nsw i32 %0, 1, !dbg !33
+  %add1 = add nsw i32 %add, 15, !dbg !34
+  ret i32 %add1, !dbg !35
+}
+
+; Function Attrs: nocallback nofree nosync nounwind speculatable willreturn memory(none)
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
+
+attributes #0 = { nounwind uwtable }
+attributes #1 = { nounwind readnone }
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!19, !20, !21, !22, !23, !24}
+!llvm.ident = !{!25}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "a", linkageName: "_ZN1C1aE", scope: !2, file: !3, line: 8, type: !5, isLocal: false, isDefinition: true, declaration: !8)
+!2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !3, producer: "clang version 18.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, retainedTypes: !4, globals: !14, splitDebugInlining: false, nameTableKind: Apple, sysroot: "/")
+!3 = !DIFile(filename: "main.cpp", directory: "/tmp", checksumkind: CSK_MD5, checksum: "b2547f7df8f54777c012dbfbd626f155")
+!4 = !{!5, !6}
+!5 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!6 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "C", file: !3, line: 1, size: 8, flags: DIFlagTypePassByValue, elements: !7, identifier: "_ZTS1C")
+!7 = !{!8, !9, !12}
+!8 = !DIDerivedType(tag: DW_TAG_variable, name: "a", scope: !6, file: !3, line: 3, baseType: !5, flags: DIFlagStaticMember)
+!9 = !DIDerivedType(tag: DW_TAG_variable, name: "b", scope: !6, file: !3, line: 4, baseType: !10, flags: DIFlagStaticMember)
+!10 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !11)
+!11 = !DIBasicType(name: "bool", size: 8, encoding: DW_ATE_boolean)
+!12 = !DIDerivedType(tag: DW_TAG_variable, name: "c", scope: !6, file: !3, line: 5, baseType: !13, flags: DIFlagStaticMember)
+!13 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !5)
+!14 = !{!0, !15, !17}
+!15 = !DIGlobalVariableExpression(var: !16, expr: !DIExpression(DW_OP_constu, 1, DW_OP_stack_value))
+!16 = distinct !DIGlobalVariable(name: "b", scope: !2, file: !3, line: 4, type: !10, isLocal: true, isDefinition: true, declaration: !9)
+!17 = !DIGlobalVariableExpression(var: !18, expr: !DIExpression(DW_OP_constu, 15, DW_OP_stack_value))
+!18 = distinct !DIGlobalVariable(name: "c", scope: !2, file: !3, line: 5, type: !13, isLocal: true, isDefinition: true, declaration: !12)
+!19 = !{i32 7, !"Dwarf Version", i32 5}
+!20 = !{i32 2, !"Debug Info Version", i32 3}
+!21 = !{i32 1, !"wchar_size", i32 4}
+!22 = !{i32 8, !"PIC Level", i32 2}
+!23 = !{i32 7, !"uwtable", i32 1}
+!24 = !{i32 7, !"frame-pointer", i32 1}
+!25 = !{!"clang version 18.0.0"}
+!26 = distinct !DISubprogram(name: "main", scope: !3, file: !3, line: 10, type: !27, scopeLine: 11, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !29)
+!27 = !DISubroutineType(types: !28)
+!28 = !{!5}
+!29 = !{}
+!30 = !DILocalVariable(name: "instance_C", scope: !26, file: !3, line: 12, type: !6)
+!31 = !DILocation(line: 12, column: 5, scope: !26)
+!32 = !DILocation(line: 13, column: 10, scope: !26)
+!33 = !DILocation(line: 13, column: 15, scope: !26)
+!34 = !DILocation(line: 13, column: 27, scope: !26)
+!35 = !DILocation(line: 13, column: 3, scope: !26)
+
+; CHECK:      .debug_info contents:
+; CHECK:      DW_TAG_variable
+; CHECK-NEXT: DW_AT_specification {{.*}} "a"
+; CHECK:      DW_TAG_structure_type
+; CHECK:      DW_AT_name {{.*}} "C"
+; CHECK:      DW_TAG_variable
+; CHECK-NEXT: DW_AT_name {{.*}} "a"
+; CHECK:      DW_AT_external
+; CHECK:      DW_AT_declaration
+; CHECK:      DW_TAG_variable
+; CHECK-NEXT: DW_AT_name {{.*}} "b"
+; CHECK:      DW_AT_external
+; CHECK:      DW_AT_declaration
+; CHECK:      DW_TAG_variable
+; CHECK-NEXT: DW_AT_name {{.*}} "c"
+; CHECK:      DW_AT_external
+; CHECK:      DW_AT_declaration
+; CHECK:      NULL
+; CHECK:      DW_TAG_variable
+; CHECK-NEXT: DW_AT_specification {{.*}} "b"
+; CHECK-NEXT: DW_AT_const_value
+; CHECK:      DW_TAG_variable
+; CHECK-NEXT: DW_AT_specification {{.*}} "c"