Reland "Add macro to suppress -Wunnecessary-virtual-specifier" (#141091)

DKLoehr · web-flow · commit 63de20c0de05 · 2025-05-28T12:15:22.000+02:00
This fixes #139614 on non-clang compilers by moving `__has_warning` completely inside the `#if defined(__clang__)` block. This prevents a parse failure from compilers which don't recognize `__has_warning`. Original description: Followup to #138741. This adds the requested macro to silence `-Wunnecessary-virtual-specifier` when declaring virtual anchor functions in `final` classes, per [LLVM policy](https://llvm.org/docs/CodingStandards.html#provide-a-virtual-method-anchor-for-classes-in-headers). It also cleans up any remaining instances of the warning, allowing us to stop disabling it when we build LLVM.
diff --git a/clang/include/clang/AST/Decl.h b/clang/include/clang/AST/Decl.h
@@ -173,7 +173,7 @@ class PragmaCommentDecl final
                     PragmaMSCommentKind CommentKind)
       : Decl(PragmaComment, TU, CommentLoc), CommentKind(CommentKind) {}
 
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
 public:
   static PragmaCommentDecl *Create(const ASTContext &C, TranslationUnitDecl *DC,
@@ -207,7 +207,7 @@ class PragmaDetectMismatchDecl final
                            size_t ValueStart)
       : Decl(PragmaDetectMismatch, TU, Loc), ValueStart(ValueStart) {}
 
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
 public:
   static PragmaDetectMismatchDecl *Create(const ASTContext &C,
@@ -5024,7 +5024,7 @@ class ImportDecl final : public Decl,
 ///   export void foo();
 /// \endcode
 class ExportDecl final : public Decl, public DeclContext {
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
 private:
   friend class ASTDeclReader;
diff --git a/clang/include/clang/AST/DeclCXX.h b/clang/include/clang/AST/DeclCXX.h
@@ -3297,7 +3297,7 @@ class LifetimeExtendedTemporaryDecl final
 
   mutable APValue *Value = nullptr;
 
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
   LifetimeExtendedTemporaryDecl(Expr *Temp, ValueDecl *EDecl, unsigned Mangling)
       : Decl(Decl::LifetimeExtendedTemporary, EDecl->getDeclContext(),
diff --git a/clang/include/clang/AST/DeclFriend.h b/clang/include/clang/AST/DeclFriend.h
@@ -52,7 +52,7 @@ class ASTContext;
 class FriendDecl final
     : public Decl,
       private llvm::TrailingObjects<FriendDecl, TemplateParameterList *> {
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
 public:
   using FriendUnion = llvm::PointerUnion<NamedDecl *, TypeSourceInfo *>;
diff --git a/clang/include/clang/AST/DeclOpenMP.h b/clang/include/clang/AST/DeclOpenMP.h
@@ -110,7 +110,7 @@ template <typename U> class OMPDeclarativeDirective : public U {
 class OMPThreadPrivateDecl final : public OMPDeclarativeDirective<Decl> {
   friend class OMPDeclarativeDirective<Decl>;
 
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
   OMPThreadPrivateDecl(DeclContext *DC = nullptr,
                        SourceLocation L = SourceLocation())
@@ -418,7 +418,7 @@ class OMPRequiresDecl final : public OMPDeclarativeDirective<Decl> {
   friend class OMPDeclarativeDirective<Decl>;
   friend class ASTDeclReader;
 
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
   OMPRequiresDecl(DeclContext *DC, SourceLocation L)
       : OMPDeclarativeDirective<Decl>(OMPRequires, DC, L) {}
@@ -475,7 +475,7 @@ class OMPAllocateDecl final : public OMPDeclarativeDirective<Decl> {
   friend class OMPDeclarativeDirective<Decl>;
   friend class ASTDeclReader;
 
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
   OMPAllocateDecl(DeclContext *DC, SourceLocation L)
       : OMPDeclarativeDirective<Decl>(OMPAllocate, DC, L) {}
diff --git a/clang/include/clang/Driver/Action.h b/clang/include/clang/Driver/Action.h
@@ -267,7 +267,7 @@ class BindArchAction : public Action {
 /// programming model implementation needs and propagates the offloading kind to
 /// its dependences.
 class OffloadAction final : public Action {
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
 public:
   /// Type used to communicate device actions. It associates bound architecture,
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
@@ -895,7 +895,7 @@ class Sema final : public SemaBase {
   /// with a vtable when the vtable is emitted. Sema is final and not
   /// polymorphic, but the debug info size savings are so significant that it is
   /// worth adding a vtable just to take advantage of this optimization.
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
   const LangOptions &getLangOpts() const { return LangOpts; }
   OpenCLOptions &getOpenCLOptions() { return OpenCLFeatures; }
diff --git a/clang/lib/AST/ByteCode/InterpFrame.h b/clang/lib/AST/ByteCode/InterpFrame.h
@@ -119,7 +119,7 @@ class InterpFrame final : public Frame {
   CodePtr getRetPC() const { return RetPC; }
 
   /// Map a location to a source.
-  virtual SourceInfo getSource(CodePtr PC) const;
+  SourceInfo getSource(CodePtr PC) const;
   const Expr *getExpr(CodePtr PC) const;
   SourceLocation getLocation(CodePtr PC) const;
   SourceRange getRange(CodePtr PC) const;
diff --git a/clang/lib/CodeGen/CGOpenMPRuntimeGPU.cpp b/clang/lib/CodeGen/CGOpenMPRuntimeGPU.cpp
@@ -323,7 +323,7 @@ class CheckVarsEscapingDeclContext final
   CheckVarsEscapingDeclContext(CodeGenFunction &CGF,
                                ArrayRef<const ValueDecl *> TeamsReductions)
       : CGF(CGF), EscapedDecls(llvm::from_range, TeamsReductions) {}
-  virtual ~CheckVarsEscapingDeclContext() = default;
+  ~CheckVarsEscapingDeclContext() = default;
   void VisitDeclStmt(const DeclStmt *S) {
     if (!S)
       return;
diff --git a/clang/lib/CodeGen/CGStmtOpenMP.cpp b/clang/lib/CodeGen/CGStmtOpenMP.cpp
@@ -4783,7 +4783,7 @@ class CheckVarsEscapingUntiedTaskDeclContext final
 
 public:
   explicit CheckVarsEscapingUntiedTaskDeclContext() = default;
-  virtual ~CheckVarsEscapingUntiedTaskDeclContext() = default;
+  ~CheckVarsEscapingUntiedTaskDeclContext() = default;
   void VisitDeclStmt(const DeclStmt *S) {
     if (!S)
       return;
diff --git a/clang/lib/Driver/ToolChains/Hexagon.h b/clang/lib/Driver/ToolChains/Hexagon.h
@@ -42,8 +42,8 @@ class LLVM_LIBRARY_VISIBILITY Linker final : public Tool {
   bool hasIntegratedCPP() const override { return false; }
   bool isLinkJob() const override { return true; }
 
-  virtual void RenderExtraToolArgs(const JobAction &JA,
-                                   llvm::opt::ArgStringList &CmdArgs) const;
+  void RenderExtraToolArgs(const JobAction &JA,
+                           llvm::opt::ArgStringList &CmdArgs) const;
   void ConstructJob(Compilation &C, const JobAction &JA,
                     const InputInfo &Output, const InputInfoList &Inputs,
                     const llvm::opt::ArgList &TCArgs,
diff --git a/llvm/cmake/modules/HandleLLVMOptions.cmake b/llvm/cmake/modules/HandleLLVMOptions.cmake
@@ -882,11 +882,6 @@ if (LLVM_ENABLE_WARNINGS AND (LLVM_COMPILER_IS_GCC_COMPATIBLE OR CLANG_CL))
   # The LLVM libraries have no stable C++ API, so -Wnoexcept-type is not useful.
   append("-Wno-noexcept-type" CMAKE_CXX_FLAGS)
 
-  # LLVM has a policy of including virtual "anchor" functions to control
-  # where the vtable is emitted. In `final` classes, these are exactly what
-  # this warning detects: unnecessary virtual methods.
-  add_flag_if_supported("-Wno-unnecessary-virtual-specifier" CXX_SUPPORTS_UNNECESSARY_VIRTUAL_FLAG)
-
   if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
     append("-Wnon-virtual-dtor" CMAKE_CXX_FLAGS)
   endif()
diff --git a/llvm/include/llvm/Analysis/InstSimplifyFolder.h b/llvm/include/llvm/Analysis/InstSimplifyFolder.h
@@ -37,7 +37,7 @@ class LLVM_ABI InstSimplifyFolder final : public IRBuilderFolder {
   TargetFolder ConstFolder;
   SimplifyQuery SQ;
 
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
 public:
   explicit InstSimplifyFolder(const DataLayout &DL) : ConstFolder(DL), SQ(DL) {}
diff --git a/llvm/include/llvm/Analysis/TargetFolder.h b/llvm/include/llvm/Analysis/TargetFolder.h
@@ -40,7 +40,7 @@ class LLVM_ABI TargetFolder final : public IRBuilderFolder {
     return ConstantFoldConstant(C, DL);
   }
 
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
 public:
   explicit TargetFolder(const DataLayout &DL) : DL(DL) {}
diff --git a/llvm/include/llvm/IR/ConstantFolder.h b/llvm/include/llvm/IR/ConstantFolder.h
@@ -28,7 +28,7 @@ namespace llvm {
 
 /// ConstantFolder - Create constants with minimum, target independent, folding.
 class ConstantFolder final : public IRBuilderFolder {
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
 public:
   explicit ConstantFolder() = default;
diff --git a/llvm/include/llvm/IR/NoFolder.h b/llvm/include/llvm/IR/NoFolder.h
@@ -33,7 +33,7 @@ namespace llvm {
 
 /// NoFolder - Create "constants" (actually, instructions) with no folding.
 class NoFolder final : public IRBuilderFolder {
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
 public:
   explicit NoFolder() = default;
diff --git a/llvm/include/llvm/Support/Compiler.h b/llvm/include/llvm/Support/Compiler.h
@@ -710,4 +710,28 @@ void AnnotateIgnoreWritesEnd(const char *file, int line);
 #define LLVM_PREFERRED_TYPE(T)
 #endif
 
+/// \macro LLVM_VIRTUAL_ANCHOR_FUNCTION
+/// This macro is used to adhere to LLVM's policy that each class with a vtable
+/// must have at least one out-of-line virtual function. This macro allows us
+/// to declare such a function in `final` classes without triggering a warning.
+// clang-format off
+// Autoformatting makes this look awful.
+#if defined(__clang__)
+  // Make sure this is only parsed if __clang__ is defined
+  #if __has_warning("-Wunnecessary-virtual-specifier")
+    #define LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION()                            \
+      _Pragma("clang diagnostic push")                                        \
+      _Pragma("clang diagnostic ignored \"-Wunnecessary-virtual-specifier\"") \
+      virtual void anchor()                                                   \
+      _Pragma("clang diagnostic pop")
+  #else // __has_warning
+    #define LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION()                            \
+      virtual void anchor()
+  #endif
+#else // defined(__clang__)
+  #define LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION()                              \
+    virtual void anchor()
+#endif
+// clang-format on
+
 #endif
diff --git a/llvm/include/llvm/Transforms/Scalar/GVNExpression.h b/llvm/include/llvm/Transforms/Scalar/GVNExpression.h
@@ -452,7 +452,7 @@ class AggregateValueExpression final : public BasicExpression {
     IntOperands[NumIntOperands++] = IntOperand;
   }
 
-  virtual void allocateIntOperands(BumpPtrAllocator &Allocator) {
+  void allocateIntOperands(BumpPtrAllocator &Allocator) {
     assert(!IntOperands && "Operands already allocated");
     IntOperands = Allocator.Allocate<unsigned>(MaxIntOperands);
   }
diff --git a/llvm/lib/Target/AMDGPU/AMDGPULowerBufferFatPointers.cpp b/llvm/lib/Target/AMDGPU/AMDGPULowerBufferFatPointers.cpp
@@ -1211,7 +1211,7 @@ class FatPtrConstMaterializer final : public ValueMaterializer {
                           ValueToValueMapTy &UnderlyingMap)
       : TypeMap(TypeMap),
         InternalMapper(UnderlyingMap, RF_None, TypeMap, this) {}
-  virtual ~FatPtrConstMaterializer() = default;
+  ~FatPtrConstMaterializer() = default;
 
   Value *materialize(Value *V) override;
 };
diff --git a/llvm/lib/Target/X86/X86InstrInfo.h b/llvm/lib/Target/X86/X86InstrInfo.h
@@ -225,7 +225,7 @@ class X86InstrInfo final : public X86GenInstrInfo {
   X86Subtarget &Subtarget;
   const X86RegisterInfo RI;
 
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
   bool analyzeBranchImpl(MachineBasicBlock &MBB, MachineBasicBlock *&TBB,
                          MachineBasicBlock *&FBB,
