Add -Wstatic-local-in-inline, which warns about using a static local

variable in a C99 inline (but not static-inline or extern-inline)
function definition.

The standard doesn't actually say that this doesn't apply to
"extern inline" definitions, but that seems like a useful extension,
and it at least doesn't have the obvious flaw that a static
mutable variable in an externally-available definition does.

rdar://13535367

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@178520 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Basic/DiagnosticGroups.td

@@ -218,6 +218,7 @@ def SizeofArrayArgument : DiagGroup<"sizeof-array-argument">;
 def SizeofArrayDecay : DiagGroup<"sizeof-array-decay">;
 def SizeofPointerMemaccess : DiagGroup<"sizeof-pointer-memaccess">;
 def StaticInInline : DiagGroup<"static-in-inline">;
+def StaticLocalInInline : DiagGroup<"static-local-in-inline">;
 def GNUStaticFloatInit : DiagGroup<"gnu-static-float-init">;
 def StaticFloatInit : DiagGroup<"static-float-init", [GNUStaticFloatInit]>;
 def StringPlusInt : DiagGroup<"string-plus-int">;

include/clang/Basic/DiagnosticSemaKinds.td

@@ -3328,6 +3328,9 @@ def warn_internal_in_extern_inline : ExtWarn<
 def ext_internal_in_extern_inline : Extension<
   "static %select{function|variable}0 %1 is used in an inline function with "
   "external linkage">, InGroup<StaticInInline>;
+def warn_static_local_in_extern_inline : Warning<
+  "non-constant static local variable in inline function may be different "
+  "in different files">, InGroup<StaticLocalInInline>;
 def note_convert_inline_to_static : Note<
   "use 'static' to give inline function %0 internal linkage">;
 def note_internal_decl_declared_here : Note<

include/clang/Sema/Sema.h

@@ -1375,6 +1375,7 @@ public:
   // Returns true if the variable declaration is a redeclaration
   bool CheckVariableDeclaration(VarDecl *NewVD, LookupResult &Previous);
   void CheckCompleteVariableDeclaration(VarDecl *var);
+  void MaybeSuggestAddingStaticToDecl(const FunctionDecl *D);
   void ActOnStartFunctionDeclarator();
   void ActOnEndFunctionDeclarator();
   NamedDecl* ActOnFunctionDeclarator(Scope* S, Declarator& D, DeclContext* DC,

lib/Sema/SemaDecl.cpp

@@ -4644,6 +4644,38 @@ static void checkAttributesAfterMerging(Sema &S, NamedDecl &ND) {
   }
 }
 
+/// Given that we are within the definition of the given function,
+/// will that definition behave like C99's 'inline', where the
+/// definition is discarded except for optimization purposes?
+static bool isFunctionDefinitionDiscarded(Sema &S, FunctionDecl *FD) {
+  // Try to avoid calling GetGVALinkageForFunction.
+
+  // All cases of this require the 'inline' keyword.
+  if (!FD->isInlined()) return false;
+
+  // This is only possible in C++ with the gnu_inline attribute.
+  if (S.getLangOpts().CPlusPlus && !FD->hasAttr<GNUInlineAttr>())
+    return false;
+
+  // Okay, go ahead and call the relatively-more-expensive function.
+
+#ifndef NDEBUG
+  // AST quite reasonably asserts that it's working on a function
+  // definition.  We don't really have a way to tell it that we're
+  // currently defining the function, so just lie to it in +Asserts
+  // builds.  This is an awful hack.
+  FD->setLazyBody(1);
+#endif
+
+  bool isC99Inline = (S.Context.GetGVALinkageForFunction(FD) == GVA_C99Inline);
+
+#ifndef NDEBUG
+  FD->setLazyBody(0);
+#endif
+
+  return isC99Inline;
+}
+
 static bool shouldConsiderLinkage(const VarDecl *VD) {
   const DeclContext *DC = VD->getDeclContext()->getRedeclContext();
   if (DC->isFunctionOrMethod())
@@ -4693,6 +4725,7 @@ Sema::ActOnVariableDeclarator(Scope *S, Declarator &D, DeclContext *DC,
     D.setInvalidType();
     SC = SC_None;
   }
+
   SCSpec = D.getDeclSpec().getStorageClassSpecAsWritten();
   VarDecl::StorageClass SCAsWritten
     = StorageClassSpecToVarDeclStorageClass(SCSpec);
@@ -4865,6 +4898,25 @@ Sema::ActOnVariableDeclarator(Scope *S, Declarator &D, DeclContext *DC,
       NewVD->setThreadSpecified(true);
   }
 
+  // C99 6.7.4p3
+  //   An inline definition of a function with external linkage shall
+  //   not contain a definition of a modifiable object with static or
+  //   thread storage duration...
+  // We only apply this when the function is required to be defined
+  // elsewhere, i.e. when the function is not 'extern inline'.  Note
+  // that a local variable with thread storage duration still has to
+  // be marked 'static'.  Also note that it's possible to get these
+  // semantics in C++ using __attribute__((gnu_inline)).
+  if (SC == SC_Static && S->getFnParent() != 0 &&
+      !NewVD->getType().isConstQualified()) {
+    FunctionDecl *CurFD = getCurFunctionDecl();
+    if (CurFD && isFunctionDefinitionDiscarded(*this, CurFD)) {
+      Diag(D.getDeclSpec().getStorageClassSpecLoc(),
+           diag::warn_static_local_in_extern_inline);
+      MaybeSuggestAddingStaticToDecl(CurFD);
+    }
+  }
+
   if (D.getDeclSpec().isModulePrivateSpecified()) {
     if (isExplicitSpecialization)
       Diag(NewVD->getLocation(), diag::err_module_private_specialization)

lib/Sema/SemaExpr.cpp

@@ -214,19 +214,24 @@ static void diagnoseUseOfInternalDeclInInlineFunction(Sema &S,
                                : diag::warn_internal_in_extern_inline)
     << /*IsVar=*/!UsedFn << D;
 
-  // Suggest "static" on the inline function, if possible.
-  if (!hasAnyExplicitStorageClass(Current)) {
-    const FunctionDecl *FirstDecl = Current->getCanonicalDecl();
-    SourceLocation DeclBegin = FirstDecl->getSourceRange().getBegin();
-    S.Diag(DeclBegin, diag::note_convert_inline_to_static)
-      << Current << FixItHint::CreateInsertion(DeclBegin, "static ");
-  }
+  S.MaybeSuggestAddingStaticToDecl(Current);
 
   S.Diag(D->getCanonicalDecl()->getLocation(),
          diag::note_internal_decl_declared_here)
     << D;
 }
 
+void Sema::MaybeSuggestAddingStaticToDecl(const FunctionDecl *Cur) {
+  const FunctionDecl *First = Cur->getFirstDeclaration();
+
+  // Suggest "static" on the function, if possible.
+  if (!hasAnyExplicitStorageClass(First)) {
+    SourceLocation DeclBegin = First->getSourceRange().getBegin();
+    Diag(DeclBegin, diag::note_convert_inline_to_static)
+      << Cur << FixItHint::CreateInsertion(DeclBegin, "static ");
+  }
+}
+
 /// \brief Determine whether the use of this declaration is valid, and
 /// emit any corresponding diagnostics.
 ///

test/Sema/inline.c

@@ -73,6 +73,16 @@ inline int useStaticAgain () { // expected-note 2 {{use 'static' to give inline
 
 #pragma clang diagnostic pop
 
+inline void defineStaticVar() { // expected-note {{use 'static' to give inline function 'defineStaticVar' internal linkage}}
+  static const int x = 0; // ok
+  static int y = 0; // expected-warning {{non-constant static local variable in inline function may be different in different files}}
+}
+
+extern inline void defineStaticVarInExtern() {
+  static const int x = 0; // ok
+  static int y = 0; // ok
+}
+
 #endif