[clang][DebugInfo] Emit global variable definitions for static data members with constant initializers

Michael137 · Michael137 · commit 81bd54091451 · 2023-11-06T09:22:39.000Z
When an LLDB user asks for the value of a static data member, LLDB starts by
searching the Names accelerator table for the corresponding variable definition
DIE. For static data members with out-of-class definitions that works fine,
because those get represented as global variables with a location and making them
eligible to be added to the Names table. However, in-class definitions won’t get
indexed because we usually don't emit global variables for them. So in DWARF
we end up with a single `DW_TAG_member` that usually holds the constant initializer.
But we don't get a corresponding CU-level `DW_TAG_variable` like we do for
out-of-class definitions.

To make it more convenient for debuggers to get to the value of inline static data members,
this patch makes sure we emit definitions for static variables with constant initializers
the same way we do for other static variables. This also aligns Clang closer to GCC, which
produces CU-level definitions for inline statics and also emits these into `.debug_pubnames`.

The implementation keeps track of newly created static data members. Then in
`CGDebugInfo::finalize`, we emit a global `DW_TAG_variable` with a `DW_AT_const_value` for
any of those declarations that didn't end up with a definition in the `DeclCache`.

The newly emitted `DW_TAG_variable` will look as follows:
```
0x0000007b:   DW_TAG_structure_type
                DW_AT_calling_convention        (DW_CC_pass_by_value)
                DW_AT_name      ("Foo")
                ...

0x0000008d:     DW_TAG_member
                  DW_AT_name    ("i")
                  DW_AT_type    (0x00000062 "const int")
                  DW_AT_external        (true)
                  DW_AT_declaration     (true)
                  DW_AT_const_value     (4)

Newly added
vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv

0x0000009a:   DW_TAG_variable
                DW_AT_specification     (0x0000008d "i")
                DW_AT_const_value       (4)
                DW_AT_linkage_name      ("_ZN2t2IiE1iIfEE")
```
diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -1693,6 +1693,7 @@ CGDebugInfo::CreateRecordStaticField(const VarDecl *Var, llvm::DIType *RecordTy,
   llvm::DIDerivedType *GV = DBuilder.createStaticMemberType(
       RecordTy, VName, VUnit, LineNumber, VTy, Flags, C, Align);
   StaticDataMemberCache[Var->getCanonicalDecl()].reset(GV);
+  StaticDataMemberDefinitionsToEmit.push_back(Var->getCanonicalDecl());
   return GV;
 }
 
@@ -5596,6 +5597,39 @@ void CGDebugInfo::EmitGlobalVariable(const ValueDecl *VD, const APValue &Init) {
       TemplateParameters, Align));
 }
 
+void CGDebugInfo::EmitGlobalVariable(const VarDecl *VD) {
+  assert(VD->hasInit());
+  assert(CGM.getCodeGenOpts().hasReducedDebugInfo());
+  if (VD->hasAttr<NoDebugAttr>())
+    return;
+
+  auto &GV = DeclCache[VD];
+  if (GV)
+    return;
+
+  auto const *InitVal = VD->evaluateValue();
+  if (!InitVal)
+    return;
+
+  llvm::DIFile *Unit = nullptr;
+  llvm::DIScope *DContext = nullptr;
+  unsigned LineNo;
+  StringRef DeclName, LinkageName;
+  QualType T;
+  llvm::MDTuple *TemplateParameters = nullptr;
+  collectVarDeclProps(VD, Unit, LineNo, T, DeclName, LinkageName,
+                      TemplateParameters, DContext);
+
+  auto Align = getDeclAlignIfRequired(VD, CGM.getContext());
+  llvm::DINodeArray Annotations = CollectBTFDeclTagAnnotations(VD);
+  llvm::DIExpression *InitExpr = createConstantValueExpression(VD, *InitVal);
+
+  GV.reset(DBuilder.createGlobalVariableExpression(
+      TheCU, DeclName, LinkageName, Unit, LineNo, getOrCreateType(T, Unit),
+      true, true, InitExpr, getOrCreateStaticDataMemberDeclarationOrNull(VD),
+      TemplateParameters, Align, Annotations));
+}
+
 void CGDebugInfo::EmitExternalVariable(llvm::GlobalVariable *Var,
                                        const VarDecl *D) {
   assert(CGM.getCodeGenOpts().hasReducedDebugInfo());
@@ -5866,6 +5900,18 @@ void CGDebugInfo::finalize() {
     DBuilder.replaceTemporary(std::move(FwdDecl), cast<llvm::MDNode>(Repl));
   }
 
+  for (auto const *VD : StaticDataMemberDefinitionsToEmit) {
+    assert (VD->isStaticDataMember());
+
+    if (auto It = DeclCache.find(VD); It != DeclCache.end())
+      continue;
+
+    if (!VD->hasInit())
+      continue;
+
+    EmitGlobalVariable(VD);
+  }
+
   // We keep our own list of retained types, because we need to look
   // up the final type in the type cache.
   for (auto &RT : RetainedTypes)
diff --git a/clang/lib/CodeGen/CGDebugInfo.h b/clang/lib/CodeGen/CGDebugInfo.h
@@ -161,6 +161,9 @@ class CGDebugInfo {
   llvm::DenseMap<const Decl *, llvm::TypedTrackingMDRef<llvm::DIDerivedType>>
       StaticDataMemberCache;
 
+  /// Keeps track of static data members for which we should emit a definition.
+  std::vector<const VarDecl *> StaticDataMemberDefinitionsToEmit;
+
   using ParamDecl2StmtTy = llvm::DenseMap<const ParmVarDecl *, const Stmt *>;
   using Param2DILocTy =
       llvm::DenseMap<const ParmVarDecl *, llvm::DILocalVariable *>;
@@ -526,6 +529,9 @@ class CGDebugInfo {
   /// Emit a constant global variable's debug info.
   void EmitGlobalVariable(const ValueDecl *VD, const APValue &Init);
 
+  /// Emit debug-info for a variable with a constant initializer.
+  void EmitGlobalVariable(const VarDecl *VD);
+
   /// Emit information about an external variable.
   void EmitExternalVariable(llvm::GlobalVariable *GV, const VarDecl *Decl);
 
diff --git a/clang/test/CodeGenCXX/debug-info-class.cpp b/clang/test/CodeGenCXX/debug-info-class.cpp
@@ -116,11 +116,19 @@ int main(int argc, char **argv) {
 // CHECK-SAME:                             DIFlagFwdDecl
 // CHECK-NOT:                             identifier:
 // CHECK-SAME:                            ){{$}}
+
+// CHECK:      !DIGlobalVariableExpression(var: ![[HDR_VAR:[0-9]+]], expr: !DIExpression(DW_OP_constu, 52, DW_OP_stack_value))
+// CHECK:      ![[HDR_VAR]] = distinct !DIGlobalVariable(name: "HdrSize",
+// CHECK-SAME:                isLocal: true, isDefinition: true, declaration: ![[HDR_VAR_DECL:[0-9]+]])
+// CHECK:      ![[INT:[0-9]+]] = !DIBasicType(name: "int"
+// CHECK:      ![[HDR_VAR_DECL]] = !DIDerivedType(tag: DW_TAG_member, name: "HdrSize"
+
+// CHECK: !DICompositeType(tag: DW_TAG_structure_type, name: "A"
+
 // CHECK: !DICompositeType(tag: DW_TAG_structure_type, name: "I"
 // CHECK-NOT:              DIFlagFwdDecl
 // CHECK-SAME:             ){{$}}
 
-// CHECK: ![[INT:[0-9]+]] = !DIBasicType(name: "int"
 // CHECK: !DICompositeType(tag: DW_TAG_structure_type, name: "foo"
 // CHECK: !DICompositeType(tag: DW_TAG_class_type, name: "bar"
 // CHECK: !DICompositeType(tag: DW_TAG_union_type, name: "baz"
@@ -186,8 +194,5 @@ int main(int argc, char **argv) {
 // CHECK: [[G_INNER_I]] = !DIDerivedType(tag: DW_TAG_member, name: "j"
 // CHECK-SAME:                           baseType: ![[INT]]
 
-// CHECK: !DICompositeType(tag: DW_TAG_structure_type, name: "A"
-// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "HdrSize"
-//
 // CHECK: ![[EXCEPTLOC]] = !DILocation(line: 100,
 // CHECK: ![[RETLOC]] = !DILocation(line: 99,
diff --git a/clang/test/CodeGenCXX/debug-info-static-inline-member.cpp b/clang/test/CodeGenCXX/debug-info-static-inline-member.cpp
@@ -0,0 +1,79 @@
+// RUN: %clangxx -target arm64-apple-macosx11.0.0 -g %s -emit-llvm -S -o - | FileCheck --check-prefixes=CHECK %s
+
+enum class Enum : int {
+  VAL = -1
+};
+
+struct Empty {};
+
+constexpr auto func() { return 25; }
+
+struct Foo {
+    static constexpr int cexpr_int = func();
+    static constexpr int cexpr_int2 = func() + 1;
+    static constexpr float cexpr_float = 2.0 + 1.0;
+    static constexpr Enum cexpr_enum = Enum::VAL;
+    static constexpr Empty cexpr_empty{};
+
+    template<typename T>
+    static constexpr T cexpr_template{};
+};
+
+int main() {
+    Foo f;
+
+    // Force global variable definitions to be emitted.
+    (void)&Foo::cexpr_int;
+    (void)&Foo::cexpr_empty;
+
+    return Foo::cexpr_int + Foo::cexpr_float
+           + (int)Foo::cexpr_enum + Foo::cexpr_template<short>;
+}
+
+// CHECK:      @{{.*}}cexpr_int{{.*}} =
+// CHECK-SAME:   !dbg ![[INT_GLOBAL:[0-9]+]]
+
+// CHECK:      @{{.*}}cexpr_empty{{.*}} = 
+// CHECK-SAME    !dbg ![[EMPTY_GLOBAL:[0-9]+]]
+
+// CHECK:      !DIGlobalVariableExpression(var: ![[INT_VAR:[0-9]+]], expr: !DIExpression())
+// CHECK:      ![[INT_VAR]] = distinct !DIGlobalVariable(name: "cexpr_int", linkageName:
+// CHECK-SAME:                isLocal: false, isDefinition: true, declaration: ![[INT_DECL:[0-9]+]])
+
+// CHECK:      ![[INT_DECL]] = !DIDerivedType(tag: DW_TAG_member, name: "cexpr_int",
+// CHECK-SAME:                 flags: DIFlagStaticMember, extraData: i32 25)
+
+// CHECK:      ![[INT_DECL2:[0-9]+]] = !DIDerivedType(tag: DW_TAG_member, name: "cexpr_int2",
+// CHECK-SAME:                         flags: DIFlagStaticMember, extraData: i32 26)
+
+// CHECK:      ![[FLOAT_DECL:[0-9]+]] = !DIDerivedType(tag: DW_TAG_member, name: "cexpr_float",
+// CHECK-SAME:                          flags: DIFlagStaticMember, extraData: float
+
+// CHECK:      ![[ENUM_DECL:[0-9]+]] = !DIDerivedType(tag: DW_TAG_member, name: "cexpr_enum",
+// CHECK-SAME:                         flags: DIFlagStaticMember, extraData: i32 -1)
+
+// CHECK:      ![[EMPTY_DECL:[0-9]+]] = !DIDerivedType(tag: DW_TAG_member, name: "cexpr_empty",
+// CHECK-SAME:                          flags: DIFlagStaticMember)
+
+// CHECK:      ![[TEMPLATE_DECL:[0-9]+]] = !DIDerivedType(tag: DW_TAG_member, name: "cexpr_template",
+// CHECK-SAME:                             flags: DIFlagStaticMember, extraData: i16 0)
+
+// CHECK:      !DIGlobalVariableExpression(var: ![[EMPTY_VAR:[0-9]+]], expr: !DIExpression())
+// CHECK:      ![[EMPTY_VAR]] = distinct !DIGlobalVariable(name: "cexpr_empty", linkageName:
+// CHECK-SAME:                  isLocal: false, isDefinition: true, declaration: ![[EMPTY_DECL]])
+
+// CHECK:      !DIGlobalVariableExpression(var: ![[INT_VAR2:[0-9]+]], expr: !DIExpression(DW_OP_constu, 26, DW_OP_stack_value))
+// CHECK:      ![[INT_VAR2]] = distinct !DIGlobalVariable(name: "cexpr_int2", linkageName:
+// CHECK-SAME:                 isLocal: true, isDefinition: true, declaration: ![[INT_DECL2]])
+
+// CHECK:      !DIGlobalVariableExpression(var: ![[FLOAT_VAR:[0-9]+]], expr: !DIExpression(DW_OP_constu, {{.*}}, DW_OP_stack_value))
+// CHECK:      ![[FLOAT_VAR]] = distinct !DIGlobalVariable(name: "cexpr_float", linkageName:
+// CHECK-SAME:                  isLocal: true, isDefinition: true, declaration: ![[FLOAT_DECL]])
+
+// CHECK:      !DIGlobalVariableExpression(var: ![[ENUM_VAR:[0-9]+]], expr: !DIExpression(DW_OP_constu, {{.*}}, DW_OP_stack_value))
+// CHECK:      ![[ENUM_VAR]] = distinct !DIGlobalVariable(name: "cexpr_enum", linkageName:
+// CHECK-SAME:                 isLocal: true, isDefinition: true, declaration: ![[ENUM_DECL]])
+
+// CHECK:      !DIGlobalVariableExpression(var: ![[TEMPLATE_VAR:[0-9]+]], expr: !DIExpression(DW_OP_constu, 0, DW_OP_stack_value))
+// CHECK:      ![[TEMPLATE_VAR]] = distinct !DIGlobalVariable(name: "cexpr_template", linkageName:
+// CHECK-SAME:                     isLocal: true, isDefinition: true, declaration: ![[TEMPLATE_DECL]], templateParams: ![[TEMPLATE_PARMS:[0-9]+]])
diff --git a/lldb/test/API/lang/cpp/const_static_integral_member/TestConstStaticIntegralMember.py b/lldb/test/API/lang/cpp/const_static_integral_member/TestConstStaticIntegralMember.py
@@ -102,9 +102,10 @@ def test(self):
         # it does not crash.
         self.expect("image lookup -t A")
 
-    # dsymutil strips the debug info for classes that only have const static
-    # data members without a definition namespace scope.
-    @expectedFailureAll(debug_info=["dsym"])
+    # For debug-info produced by older versions of clang, dsymutil strips the
+    # debug info for classes that only have const static data members without
+    # definitions.
+    @expectedFailureAll(compiler=["clang"], compiler_version=["<", "18.0"])
     def test_class_with_only_const_static(self):
         self.build()
         lldbutil.run_to_source_breakpoint(
