Implement C++17 P0386R2, inline variables. (The 'inline' specifier gives a

variable weak discardable linkage and partially-ordered initialization, and is
implied for constexpr static data members.)

llvm-svn: 273754

Author: zygoloid

clang/include/clang/AST/Decl.h

@@ -881,6 +881,12 @@ class VarDecl : public DeclaratorDecl, public Redeclarable<VarDecl> {
     /// variable;  see isARCPseudoStrong() for details.
     unsigned ARCPseudoStrong : 1;
 
+    /// \brief Whether this variable is (C++1z) inline.
+    unsigned IsInline : 1;
+
+    /// \brief Whether this variable has (C++1z) inline explicitly specified.
+    unsigned IsInlineSpecified : 1;
+
     /// \brief Whether this variable is (C++0x) constexpr.
     unsigned IsConstexpr : 1;
 
@@ -1102,9 +1108,6 @@ class VarDecl : public DeclaratorDecl, public Redeclarable<VarDecl> {
   /// definition of a static data member.
   bool isOutOfLine() const override;
 
-  /// \brief If this is a static data member, find its out-of-line definition.
-  VarDecl *getOutOfLineDefinition();
-
   /// isFileVarDecl - Returns true for file scoped variable declaration.
   bool isFileVarDecl() const {
     Kind K = getKind();
@@ -1250,6 +1253,24 @@ class VarDecl : public DeclaratorDecl, public Redeclarable<VarDecl> {
     NonParmVarDeclBits.ARCPseudoStrong = ps;
   }
 
+  /// Whether this variable is (C++1z) inline.
+  bool isInline() const {
+    return isa<ParmVarDecl>(this) ? false : NonParmVarDeclBits.IsInline;
+  }
+  bool isInlineSpecified() const {
+    return isa<ParmVarDecl>(this) ? false
+                                  : NonParmVarDeclBits.IsInlineSpecified;
+  }
+  void setInlineSpecified() {
+    assert(!isa<ParmVarDecl>(this));
+    NonParmVarDeclBits.IsInline = true;
+    NonParmVarDeclBits.IsInlineSpecified = true;
+  }
+  void setImplicitlyInline() {
+    assert(!isa<ParmVarDecl>(this));
+    NonParmVarDeclBits.IsInline = true;
+  }
+
   /// Whether this variable is (C++11) constexpr.
   bool isConstexpr() const {
     return isa<ParmVarDecl>(this) ? false : NonParmVarDeclBits.IsConstexpr;

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -339,12 +339,16 @@ def err_language_linkage_spec_not_ascii : Error<
 def warn_use_out_of_scope_declaration : Warning<
   "use of out-of-scope declaration of %0">;
 def err_inline_non_function : Error<
-  "'inline' can only appear on functions">;
+  "'inline' can only appear on functions%select{| and non-local variables}0">;
 def err_noreturn_non_function : Error<
   "'_Noreturn' can only appear on functions">;
 def warn_qual_return_type : Warning< 
   "'%0' type qualifier%s1 on return type %plural{1:has|:have}1 no effect">,
   InGroup<IgnoredQualifiers>, DefaultIgnore;
+def warn_deprecated_redundant_constexpr_static_def : Warning<
+  "out-of-line definition of constexpr static data member is redundant "
+  "in C++17 and is deprecated">,
+  InGroup<Deprecated>, DefaultIgnore;
 
 def warn_decl_shadow :
   Warning<"declaration shadows a %select{"
@@ -1086,6 +1090,12 @@ def warn_cxx14_compat_static_assert_no_message : Warning<
   "static_assert with no message is incompatible with C++ standards before C++1z">,
   DefaultIgnore, InGroup<CXXPre1zCompat>;
 
+def ext_inline_variable : ExtWarn<
+  "inline variables are a C++1z extension">, InGroup<CXX1z>;
+def warn_cxx14_compat_inline_variable : Warning<
+  "inline variables are incompatible with C++ standards before C++1z">,
+  DefaultIgnore, InGroup<CXXPre1zCompat>;
+
 def warn_inline_namespace_reopened_noninline : Warning<
   "inline namespace cannot be reopened as a non-inline namespace">;
 def err_inline_namespace_mismatch : Error<
@@ -4305,6 +4315,7 @@ def warn_undefined_internal : Warning<
   InGroup<DiagGroup<"undefined-internal">>;
 def warn_undefined_inline : Warning<"inline function %q0 is not defined">,
   InGroup<DiagGroup<"undefined-inline">>;
+def err_undefined_inline_var : Error<"inline variable %q0 is not defined">;
 def note_used_here : Note<"used here">;
 
 def err_internal_linkage_redeclaration : Error<

clang/include/clang/Sema/SemaInternal.h

@@ -73,10 +73,11 @@ inline void MarkVarDeclODRUsed(VarDecl *Var,
   // Keep track of used but undefined variables.
   // FIXME: We shouldn't suppress this warning for static data members.
   if (Var->hasDefinition(SemaRef.Context) == VarDecl::DeclarationOnly &&
-    !Var->isExternallyVisible() &&
-    !(Var->isStaticDataMember() && Var->hasInit())) {
-      SourceLocation &old = SemaRef.UndefinedButUsed[Var->getCanonicalDecl()];
-      if (old.isInvalid()) old = Loc;
+      (!Var->isExternallyVisible() || Var->isInline()) &&
+      !(Var->isStaticDataMember() && Var->hasInit())) {
+    SourceLocation &old = SemaRef.UndefinedButUsed[Var->getCanonicalDecl()];
+    if (old.isInvalid())
+      old = Loc;
   }
   QualType CaptureType, DeclRefType;
   SemaRef.tryCaptureVariable(Var, Loc, Sema::TryCapture_Implicit, 

clang/lib/AST/ASTContext.cpp

@@ -8486,15 +8486,19 @@ static GVALinkage basicGVALinkageForVariable(const ASTContext &Context,
   if (Context.isMSStaticDataMemberInlineDefinition(VD))
     return GVA_DiscardableODR;
 
+  GVALinkage StrongLinkage = GVA_StrongExternal;
+  if (VD->isInline())
+    StrongLinkage = GVA_DiscardableODR;
+
   switch (VD->getTemplateSpecializationKind()) {
   case TSK_Undeclared:
-    return GVA_StrongExternal;
+    return StrongLinkage;
 
   case TSK_ExplicitSpecialization:
     return Context.getTargetInfo().getCXXABI().isMicrosoft() &&
                    VD->isStaticDataMember()
                ? GVA_StrongODR
-               : GVA_StrongExternal;
+               : StrongLinkage;
 
   case TSK_ExplicitInstantiationDefinition:
     return GVA_StrongODR;

clang/lib/AST/ASTDumper.cpp

@@ -1196,6 +1196,10 @@ void ASTDumper::VisitVarDecl(const VarDecl *D) {
     OS << " __module_private__";
   if (D->isNRVOVariable())
     OS << " nrvo";
+  if (D->isInline())
+    OS << " inline";
+  if (D->isConstexpr())
+    OS << " constexpr";
   if (D->hasInit()) {
     switch (D->getInitStyle()) {
     case VarDecl::CInit: OS << " cinit"; break;

clang/lib/AST/Decl.cpp

@@ -592,12 +592,14 @@ static LinkageInfo getLVForNamespaceScopeDecl(const NamedDecl *D,
     if (Var->getStorageClass() == SC_Static)
       return LinkageInfo::internal();
 
-    // - a non-volatile object or reference that is explicitly declared const
-    //   or constexpr and neither explicitly declared extern nor previously
-    //   declared to have external linkage; or (there is no equivalent in C99)
+    // - a non-inline, non-volatile object or reference that is explicitly
+    //   declared const or constexpr and neither explicitly declared extern
+    //   nor previously declared to have external linkage; or (there is no
+    //   equivalent in C99)
     if (Context.getLangOpts().CPlusPlus &&
         Var->getType().isConstQualified() && 
-        !Var->getType().isVolatileQualified()) {
+        !Var->getType().isVolatileQualified() &&
+        !Var->isInline()) {
       const VarDecl *PrevVar = Var->getPreviousDecl();
       if (PrevVar)
         return getLVForDecl(PrevVar, computation);
@@ -1912,7 +1914,9 @@ VarDecl::isThisDeclarationADefinition(ASTContext &C) const {
   // C++ [basic.def]p2:
   //   A declaration is a definition unless [...] it contains the 'extern'
   //   specifier or a linkage-specification and neither an initializer [...],
-  //   it declares a static data member in a class declaration [...].
+  //   it declares a non-inline static data member in a class declaration [...],
+  //   it declares a static data member outside a class definition and the variable
+  //   was defined within the class with the constexpr specifier [...],
   // C++1y [temp.expl.spec]p15:
   //   An explicit specialization of a static data member or an explicit
   //   specialization of a static data member template is a definition if the
@@ -1922,6 +1926,8 @@ VarDecl::isThisDeclarationADefinition(ASTContext &C) const {
   // a static data member template outside the containing class?
   if (isStaticDataMember()) {
     if (isOutOfLine() &&
+        !(getCanonicalDecl()->isInline() &&
+          getCanonicalDecl()->isConstexpr()) &&
         (hasInit() ||
          // If the first declaration is out-of-line, this may be an
          // instantiation of an out-of-line partial specialization of a variable
@@ -1932,6 +1938,8 @@ VarDecl::isThisDeclarationADefinition(ASTContext &C) const {
                     TSK_ExplicitSpecialization) ||
          isa<VarTemplatePartialSpecializationDecl>(this)))
       return Definition;
+    else if (!isOutOfLine() && isInline())
+      return Definition;
     else
       return DeclarationOnly;
   }
@@ -2072,18 +2080,6 @@ bool VarDecl::isOutOfLine() const {
   return false;
 }
 
-VarDecl *VarDecl::getOutOfLineDefinition() {
-  if (!isStaticDataMember())
-    return nullptr;
-
-  for (auto RD : redecls()) {
-    if (RD->getLexicalDeclContext()->isFileContext())
-      return RD;
-  }
-
-  return nullptr;
-}
-
 void VarDecl::setInit(Expr *I) {
   if (auto *Eval = Init.dyn_cast<EvaluatedStmt *>()) {
     Eval->~EvaluatedStmt();

clang/lib/CodeGen/CodeGenModule.cpp

@@ -3746,6 +3746,12 @@ void CodeGenModule::EmitTopLevelDecl(Decl *D) {
   case Decl::Namespace:
     EmitNamespace(cast<NamespaceDecl>(D));
     break;
+  case Decl::CXXRecord:
+    // Emit any static data members, they may be definitions.
+    for (auto *I : cast<CXXRecordDecl>(D)->decls())
+      if (isa<VarDecl>(I) || isa<CXXRecordDecl>(I))
+        EmitTopLevelDecl(I);
+    break;
     // No code generation needed.
   case Decl::UsingShadow:
   case Decl::ClassTemplate:

clang/lib/CodeGen/ItaniumCXXABI.cpp

@@ -1905,10 +1905,18 @@ void ItaniumCXXABI::EmitGuardedInit(CodeGenFunction &CGF,
                                     bool shouldPerformInit) {
   CGBuilderTy &Builder = CGF.Builder;
 
-  // We only need to use thread-safe statics for local non-TLS variables;
-  // global initialization is always single-threaded.
+  // Inline variables that weren't instantiated from variable templates have
+  // partially-ordered initialization within their translation unit.
+  bool NonTemplateInline =
+      D.isInline() &&
+      !isTemplateInstantiation(D.getTemplateSpecializationKind());
+
+  // We only need to use thread-safe statics for local non-TLS variables and
+  // inline variables; other global initialization is always single-threaded
+  // or (through lazy dynamic loading in multiple threads) unsequenced.
   bool threadsafe = getContext().getLangOpts().ThreadsafeStatics &&
-                    D.isLocalVarDecl() && !D.getTLSKind();
+                    (D.isLocalVarDecl() || NonTemplateInline) &&
+                    !D.getTLSKind();
 
   // If we have a global variable with internal linkage and thread-safe statics
   // are disabled, we can just let the guard variable be of type i8.
@@ -1962,7 +1970,11 @@ void ItaniumCXXABI::EmitGuardedInit(CodeGenFunction &CGF,
     if (!D.isLocalVarDecl() && C &&
         CGM.getTarget().getTriple().isOSBinFormatELF()) {
       guard->setComdat(C);
-      CGF.CurFn->setComdat(C);
+      // An inline variable's guard function is run from the per-TU
+      // initialization function, not via a dedicated global ctor function, so
+      // we can't put it in a comdat.
+      if (!NonTemplateInline)
+        CGF.CurFn->setComdat(C);
     } else if (CGM.supportsCOMDAT() && guard->isWeakForLinker()) {
       guard->setComdat(CGM.getModule().getOrInsertComdat(guard->getName()));
     }

clang/lib/Sema/Sema.cpp

@@ -469,7 +469,8 @@ static bool ShouldRemoveFromUnused(Sema *SemaRef, const DeclaratorDecl *D) {
   return false;
 }
 
-/// Obtains a sorted list of functions that are undefined but ODR-used.
+/// Obtains a sorted list of functions and variables that are undefined but
+/// ODR-used.
 void Sema::getUndefinedButUsed(
     SmallVectorImpl<std::pair<NamedDecl *, SourceLocation> > &Undefined) {
   for (const auto &UndefinedUse : UndefinedButUsed) {
@@ -488,9 +489,10 @@ void Sema::getUndefinedButUsed(
           !FD->getMostRecentDecl()->isInlined())
         continue;
     } else {
-      if (cast<VarDecl>(ND)->hasDefinition() != VarDecl::DeclarationOnly)
+      auto *VD = cast<VarDecl>(ND);
+      if (VD->hasDefinition() != VarDecl::DeclarationOnly)
         continue;
-      if (ND->isExternallyVisible())
+      if (VD->isExternallyVisible() && !VD->getMostRecentDecl()->isInline())
         continue;
     }
 
@@ -522,10 +524,15 @@ static void checkUndefinedButUsed(Sema &S) {
     if (!ND->isExternallyVisible()) {
       S.Diag(ND->getLocation(), diag::warn_undefined_internal)
         << isa<VarDecl>(ND) << ND;
-    } else {
-      assert(cast<FunctionDecl>(ND)->getMostRecentDecl()->isInlined() &&
+    } else if (auto *FD = dyn_cast<FunctionDecl>(ND)) {
+      assert(FD->getMostRecentDecl()->isInlined() &&
              "used object requires definition but isn't inline or internal?");
+      // FIXME: This is ill-formed; we should reject.
       S.Diag(ND->getLocation(), diag::warn_undefined_inline) << ND;
+    } else {
+      assert(cast<VarDecl>(ND)->getMostRecentDecl()->isInline() &&
+             "used var requires definition but isn't inline or internal?");
+      S.Diag(ND->getLocation(), diag::err_undefined_inline_var) << ND;
     }
     if (I->second.isValid())
       S.Diag(I->second, diag::note_used_here);