Don't warn on "use" of undefined inline function that isn't actually an ODR

use. In order for this to fire, the function needed to be a templated function
marked 'constexpr' and declared but not defined. This weird pattern appears in
libstdc++'s alloc_traits.h.

llvm-svn: 264471

clang/include/clang/Sema/Sema.h

@@ -3593,9 +3593,15 @@ public:
   // for expressions referring to a decl; these exist because odr-use marking
   // needs to be delayed for some constant variables when we build one of the
   // named expressions.
-  void MarkAnyDeclReferenced(SourceLocation Loc, Decl *D, bool OdrUse);
+  //
+  // MightBeOdrUse indicates whether the use could possibly be an odr-use, and
+  // should usually be true. This only needs to be set to false if the lack of
+  // odr-use cannot be determined from the current context (for instance,
+  // because the name denotes a virtual function and was written without an
+  // explicit nested-name-specifier).
+  void MarkAnyDeclReferenced(SourceLocation Loc, Decl *D, bool MightBeOdrUse);
   void MarkFunctionReferenced(SourceLocation Loc, FunctionDecl *Func,
-                              bool OdrUse = true);
+                              bool MightBeOdrUse = true);
   void MarkVariableReferenced(SourceLocation Loc, VarDecl *Var);
   void MarkDeclRefReferenced(DeclRefExpr *E);
   void MarkMemberReferenced(MemberExpr *E);

clang/lib/Sema/SemaExpr.cpp

@@ -12770,7 +12770,7 @@ static bool IsPotentiallyEvaluatedContext(Sema &SemaRef) {
 /// \brief Mark a function referenced, and check whether it is odr-used
 /// (C++ [basic.def.odr]p2, C99 6.9p3)
 void Sema::MarkFunctionReferenced(SourceLocation Loc, FunctionDecl *Func,
-                                  bool OdrUse) {
+                                  bool MightBeOdrUse) {
   assert(Func && "No function?");
 
   Func->setReferenced();
@@ -12783,8 +12783,8 @@ void Sema::MarkFunctionReferenced(SourceLocation Loc, FunctionDecl *Func,
   // We (incorrectly) mark overload resolution as an unevaluated context, so we
   // can just check that here. Skip the rest of this function if we've already
   // marked the function as used.
-  if (Func->isUsed(/*CheckUsedAttr=*/false) ||
-      !IsPotentiallyEvaluatedContext(*this)) {
+  bool OdrUse = MightBeOdrUse && IsPotentiallyEvaluatedContext(*this);
+  if (Func->isUsed(/*CheckUsedAttr=*/false) || !OdrUse) {
     // C++11 [temp.inst]p3:
     //   Unless a function template specialization has been explicitly
     //   instantiated or explicitly specialized, the function template
@@ -12873,8 +12873,6 @@ void Sema::MarkFunctionReferenced(SourceLocation Loc, FunctionDecl *Func,
   if (FPT && isUnresolvedExceptionSpec(FPT->getExceptionSpecType()))
     ResolveExceptionSpec(Loc, FPT);
 
-  if (!OdrUse) return;
-
   // Implicit instantiation of function templates and member functions of
   // class templates.
   if (Func->isImplicitlyInstantiable()) {
@@ -12922,10 +12920,12 @@ void Sema::MarkFunctionReferenced(SourceLocation Loc, FunctionDecl *Func,
     // Walk redefinitions, as some of them may be instantiable.
     for (auto i : Func->redecls()) {
       if (!i->isUsed(false) && i->isImplicitlyInstantiable())
-        MarkFunctionReferenced(Loc, i);
+        MarkFunctionReferenced(Loc, i, OdrUse);
     }
   }
 
+  if (!OdrUse) return;
+
   // Keep track of used but undefined functions.
   if (!Func->isDefined()) {
     if (mightHaveNonExternalLinkage(Func))
@@ -13800,13 +13800,13 @@ void Sema::MarkVariableReferenced(SourceLocation Loc, VarDecl *Var) {
 }
 
 static void MarkExprReferenced(Sema &SemaRef, SourceLocation Loc,
-                               Decl *D, Expr *E, bool OdrUse) {
+                               Decl *D, Expr *E, bool MightBeOdrUse) {
   if (VarDecl *Var = dyn_cast<VarDecl>(D)) {
     DoMarkVarDeclReferenced(SemaRef, Loc, Var, E);
     return;
   }
 
-  SemaRef.MarkAnyDeclReferenced(Loc, D, OdrUse);
+  SemaRef.MarkAnyDeclReferenced(Loc, D, MightBeOdrUse);
 
   // If this is a call to a method via a cast, also mark the method in the
   // derived class used in case codegen can devirtualize the call.
@@ -13828,7 +13828,7 @@ static void MarkExprReferenced(Sema &SemaRef, SourceLocation Loc,
   CXXMethodDecl *DM = MD->getCorrespondingMethodInClass(MostDerivedClassDecl);
   if (!DM || DM->isPure())
     return;
-  SemaRef.MarkAnyDeclReferenced(Loc, DM, OdrUse);
+  SemaRef.MarkAnyDeclReferenced(Loc, DM, MightBeOdrUse);
 } 
 
 /// \brief Perform reference-marking and odr-use handling for a DeclRefExpr.
@@ -13851,30 +13851,31 @@ void Sema::MarkMemberReferenced(MemberExpr *E) {
   //   overload resolution when referred to from a potentially-evaluated
   //   expression, is odr-used, unless it is a pure virtual function and its
   //   name is not explicitly qualified.
-  bool OdrUse = true;
+  bool MightBeOdrUse = true;
   if (E->performsVirtualDispatch(getLangOpts())) {
     if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(E->getMemberDecl()))
       if (Method->isPure())
-        OdrUse = false;
+        MightBeOdrUse = false;
   }
   SourceLocation Loc = E->getMemberLoc().isValid() ?
                             E->getMemberLoc() : E->getLocStart();
-  MarkExprReferenced(*this, Loc, E->getMemberDecl(), E, OdrUse);
+  MarkExprReferenced(*this, Loc, E->getMemberDecl(), E, MightBeOdrUse);
 }
 
 /// \brief Perform marking for a reference to an arbitrary declaration.  It
 /// marks the declaration referenced, and performs odr-use checking for
 /// functions and variables. This method should not be used when building a
 /// normal expression which refers to a variable.
-void Sema::MarkAnyDeclReferenced(SourceLocation Loc, Decl *D, bool OdrUse) {
-  if (OdrUse) {
+void Sema::MarkAnyDeclReferenced(SourceLocation Loc, Decl *D,
+                                 bool MightBeOdrUse) {
+  if (MightBeOdrUse) {
     if (auto *VD = dyn_cast<VarDecl>(D)) {
       MarkVariableReferenced(Loc, VD);
       return;
     }
   }
   if (auto *FD = dyn_cast<FunctionDecl>(D)) {
-    MarkFunctionReferenced(Loc, FD, OdrUse);
+    MarkFunctionReferenced(Loc, FD, MightBeOdrUse);
     return;
   }
   D->setReferenced();

clang/test/SemaCXX/undefined-inline.cpp

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsyntax-only -triple i686-pc-win32 -verify %s
+// RUN: %clang_cc1 -fsyntax-only -triple i686-pc-win32 -verify -std=c++11 %s
 // PR14993
 
 namespace test1 {
@@ -61,3 +61,8 @@ namespace test11 {
   inline void bar() __attribute__((dllimport));
   void test() { foo(); bar(); }
 }
+
+namespace test12 {
+  template<typename> constexpr int _S_chk(int *);
+  decltype(_S_chk<int>(nullptr)) n;
+}