[clang] Replace LLVM_ATTRIBUTE_UNUSED with [[maybe_unused]] (NFC) (#163914)

This patch replaces LLVM_ATTRIBUTE_UNUSED with [[maybe_unused]],
introduced as part of C++17.

Author: kazutakahirata

clang/include/clang/CIR/Dialect/IR/CIROpsEnums.h

@@ -54,19 +54,18 @@ static bool isLocalLinkage(GlobalLinkageKind linkage) {
 static bool isExternalWeakLinkage(GlobalLinkageKind linkage) {
   return linkage == GlobalLinkageKind::ExternalWeakLinkage;
 }
-LLVM_ATTRIBUTE_UNUSED static bool isCommonLinkage(GlobalLinkageKind linkage) {
+[[maybe_unused]] static bool isCommonLinkage(GlobalLinkageKind linkage) {
   return linkage == GlobalLinkageKind::CommonLinkage;
 }
-LLVM_ATTRIBUTE_UNUSED static bool
+[[maybe_unused]] static bool
 isValidDeclarationLinkage(GlobalLinkageKind linkage) {
   return isExternalWeakLinkage(linkage) || isExternalLinkage(linkage);
 }
 
 /// Whether the definition of this global may be replaced by something
 /// non-equivalent at link time. For example, if a function has weak linkage
 /// then the code defining it may be replaced by different code.
-LLVM_ATTRIBUTE_UNUSED static bool
-isInterposableLinkage(GlobalLinkageKind linkage) {
+[[maybe_unused]] static bool isInterposableLinkage(GlobalLinkageKind linkage) {
   switch (linkage) {
   case GlobalLinkageKind::WeakAnyLinkage:
   case GlobalLinkageKind::LinkOnceAnyLinkage:
@@ -89,8 +88,7 @@ isInterposableLinkage(GlobalLinkageKind linkage) {
 
 /// Whether the definition of this global may be discarded if it is not used
 /// in its compilation unit.
-LLVM_ATTRIBUTE_UNUSED static bool
-isDiscardableIfUnused(GlobalLinkageKind linkage) {
+[[maybe_unused]] static bool isDiscardableIfUnused(GlobalLinkageKind linkage) {
   return isLinkOnceLinkage(linkage) || isLocalLinkage(linkage) ||
          isAvailableExternallyLinkage(linkage);
 }
@@ -99,7 +97,7 @@ isDiscardableIfUnused(GlobalLinkageKind linkage) {
 /// Using this method outside of the code generators is almost always a
 /// mistake: when working at the IR level use isInterposable instead as it
 /// knows about ODR semantics.
-LLVM_ATTRIBUTE_UNUSED static bool isWeakForLinker(GlobalLinkageKind linkage) {
+[[maybe_unused]] static bool isWeakForLinker(GlobalLinkageKind linkage) {
   return linkage == GlobalLinkageKind::WeakAnyLinkage ||
          linkage == GlobalLinkageKind::WeakODRLinkage ||
          linkage == GlobalLinkageKind::LinkOnceAnyLinkage ||
@@ -108,7 +106,7 @@ LLVM_ATTRIBUTE_UNUSED static bool isWeakForLinker(GlobalLinkageKind linkage) {
          linkage == GlobalLinkageKind::ExternalWeakLinkage;
 }
 
-LLVM_ATTRIBUTE_UNUSED static bool isValidLinkage(GlobalLinkageKind gl) {
+[[maybe_unused]] static bool isValidLinkage(GlobalLinkageKind gl) {
   return isExternalLinkage(gl) || isLocalLinkage(gl) || isWeakLinkage(gl) ||
          isLinkOnceLinkage(gl);
 }

clang/lib/AST/ByteCode/InterpBuiltin.cpp

@@ -23,7 +23,7 @@
 namespace clang {
 namespace interp {
 
-LLVM_ATTRIBUTE_UNUSED static bool isNoopBuiltin(unsigned ID) {
+[[maybe_unused]] static bool isNoopBuiltin(unsigned ID) {
   switch (ID) {
   case Builtin::BIas_const:
   case Builtin::BIforward:

clang/lib/AST/Comment.cpp

@@ -56,16 +56,16 @@ good implements_child_begin_end(Comment::child_iterator (T::*)() const) {
   return good();
 }
 
-LLVM_ATTRIBUTE_UNUSED
-static inline bad implements_child_begin_end(
-                      Comment::child_iterator (Comment::*)() const) {
+[[maybe_unused]]
+static inline bad
+implements_child_begin_end(Comment::child_iterator (Comment::*)() const) {
   return bad();
 }
 
 #define ASSERT_IMPLEMENTS_child_begin(function) \
   (void) good(implements_child_begin_end(function))
 
-LLVM_ATTRIBUTE_UNUSED
+[[maybe_unused]]
 static inline void CheckCommentASTNodes() {
 #define ABSTRACT_COMMENT(COMMENT)
 #define COMMENT(CLASS, PARENT) \

clang/lib/AST/Stmt.cpp

@@ -252,7 +252,7 @@ namespace {
   template <class T> good implements_children(children_t T::*) {
     return good();
   }
-  LLVM_ATTRIBUTE_UNUSED
+  [[maybe_unused]]
   static bad implements_children(children_t Stmt::*) {
     return bad();
   }
@@ -261,15 +261,19 @@ namespace {
   template <class T> good implements_getBeginLoc(getBeginLoc_t T::*) {
     return good();
   }
-  LLVM_ATTRIBUTE_UNUSED
-  static bad implements_getBeginLoc(getBeginLoc_t Stmt::*) { return bad(); }
+  [[maybe_unused]]
+  static bad implements_getBeginLoc(getBeginLoc_t Stmt::*) {
+    return bad();
+  }
 
   typedef SourceLocation getLocEnd_t() const;
   template <class T> good implements_getEndLoc(getLocEnd_t T::*) {
     return good();
   }
-  LLVM_ATTRIBUTE_UNUSED
-  static bad implements_getEndLoc(getLocEnd_t Stmt::*) { return bad(); }
+  [[maybe_unused]]
+  static bad implements_getEndLoc(getLocEnd_t Stmt::*) {
+    return bad();
+  }
 
 #define ASSERT_IMPLEMENTS_children(type) \
   (void) is_good(implements_children(&type::children))
@@ -282,7 +286,7 @@ namespace {
 
 /// Check whether the various Stmt classes implement their member
 /// functions.
-LLVM_ATTRIBUTE_UNUSED
+[[maybe_unused]]
 static inline void check_implementations() {
 #define ABSTRACT_STMT(type)
 #define STMT(type, base)                                                       \

clang/lib/AST/StmtPrinter.cpp

@@ -151,11 +151,11 @@ namespace {
       else StmtVisitor<StmtPrinter>::Visit(S);
     }
 
-    void VisitStmt(Stmt *Node) LLVM_ATTRIBUTE_UNUSED {
+    [[maybe_unused]] void VisitStmt(Stmt *Node) {
       Indent() << "<<unknown stmt type>>" << NL;
     }
 
-    void VisitExpr(Expr *Node) LLVM_ATTRIBUTE_UNUSED {
+    [[maybe_unused]] void VisitExpr(Expr *Node) {
       OS << "<<unknown expr type>>";
     }
 

clang/lib/CIR/CodeGen/CIRGenExprConstant.cpp

@@ -871,7 +871,7 @@ bool ConstRecordBuilder::updateRecord(ConstantEmitter &emitter,
 class ConstExprEmitter
     : public StmtVisitor<ConstExprEmitter, mlir::Attribute, QualType> {
   CIRGenModule &cgm;
-  LLVM_ATTRIBUTE_UNUSED ConstantEmitter &emitter;
+  [[maybe_unused]] ConstantEmitter &emitter;
 
 public:
   ConstExprEmitter(ConstantEmitter &emitter)

clang/lib/CIR/CodeGen/CIRGenValue.h

@@ -308,7 +308,7 @@ class AggValueSlot {
   /// destructor for the slot.  Otherwise the code which constructs it should
   /// push the appropriate cleanup.
   LLVM_PREFERRED_TYPE(bool)
-  LLVM_ATTRIBUTE_UNUSED unsigned destructedFlag : 1;
+  [[maybe_unused]] unsigned destructedFlag : 1;
 
   /// This is set to true if the memory in the slot is known to be zero before
   /// the assignment into it.  This means that zero fields don't need to be set.
@@ -327,15 +327,15 @@ class AggValueSlot {
   /// object, it's important that this flag never be set when
   /// evaluating an expression which constructs such an object.
   LLVM_PREFERRED_TYPE(bool)
-  LLVM_ATTRIBUTE_UNUSED unsigned aliasedFlag : 1;
+  [[maybe_unused]] unsigned aliasedFlag : 1;
 
   /// This is set to true if the tail padding of this slot might overlap
   /// another object that may have already been initialized (and whose
   /// value must be preserved by this initialization). If so, we may only
   /// store up to the dsize of the type. Otherwise we can widen stores to
   /// the size of the type.
   LLVM_PREFERRED_TYPE(bool)
-  LLVM_ATTRIBUTE_UNUSED unsigned overlapFlag : 1;
+  [[maybe_unused]] unsigned overlapFlag : 1;
 
 public:
   enum IsDestructed_t { IsNotDestructed, IsDestructed };

clang/lib/CodeGen/CodeGenTBAA.cpp

@@ -609,8 +609,7 @@ llvm::MDNode *CodeGenTBAA::getValidBaseTypeInfo(QualType QTy) {
   // First calculate the metadata, before recomputing the insertion point, as
   // the helper can recursively call us.
   llvm::MDNode *TypeNode = getBaseTypeInfoHelper(Ty);
-  LLVM_ATTRIBUTE_UNUSED auto inserted =
-      BaseTypeMetadataCache.insert({Ty, TypeNode});
+  [[maybe_unused]] auto inserted = BaseTypeMetadataCache.insert({Ty, TypeNode});
   assert(inserted.second && "BaseType metadata was already inserted");
 
   return TypeNode;

clang/lib/Format/UnwrappedLineParser.cpp

@@ -60,7 +60,7 @@ void printLine(llvm::raw_ostream &OS, const UnwrappedLine &Line,
     OS << "\n";
 }
 
-LLVM_ATTRIBUTE_UNUSED static void printDebugInfo(const UnwrappedLine &Line) {
+[[maybe_unused]] static void printDebugInfo(const UnwrappedLine &Line) {
   printLine(llvm::dbgs(), Line);
 }
 

clang/lib/StaticAnalyzer/Core/BasicValueFactory.cpp

@@ -173,7 +173,7 @@ const PointerToMemberData *BasicValueFactory::getPointerToMemberData(
   return D;
 }
 
-LLVM_ATTRIBUTE_UNUSED static bool hasNoRepeatedElements(
+[[maybe_unused]] static bool hasNoRepeatedElements(
     llvm::ImmutableList<const CXXBaseSpecifier *> BaseSpecList) {
   llvm::SmallPtrSet<QualType, 16> BaseSpecSeen;
   for (const CXXBaseSpecifier *BaseSpec : BaseSpecList) {