PR23923: "redefine_extname" pragma handled incorrectly in case of a local var with the same name

[andreybokhanko]

Summary

As Richard Smith noted in his review (http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20150608/130447.html), pragma "redefine_extname" doesn't work correctly when there is a local of the same name. The patch fixes this.

[andreybokhanko]

Patch updated in response to Aaron Ballman's comments (http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20150622/131513.html).

[andreybokhanko]

Patch updated in response to Aaron Ballman's comments (http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20150622/131538.html).

[andreybokhanko]

Patch updated in response to Aaron Ballman's comment (http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20150622/131626.html).

Aaron, everything fixed according to your comments (including adding a new test).

[andreybokhanko]

test/CodeGenCXX/redefine_extname.cpp test fixed

[andreybokhanko]

Accepted after Aaron's LGTM.

Aaron, thank you for the review!

I don't have commit access yet; Alexander [Musman], could you, please, commit this patch?

[aaron.ballman]

I am not Alexander Musman, but I commit your patch anyway. ;-) It's in r240653.

Thanks!

~Aaron

lib/Sema/SemaDecl.cpp

bool Sema::adjustContextForLocalExternDecl(DeclContext *&DC) {
   //
   // Per C++11 [namespace.def]p6, the innermost enclosing namespace is a
   // semantically-enclosing namespace, not a lexically-enclosing one.
   while (!DC->isFileContext() && !isa<LinkageSpecDecl>(DC))
     DC = DC->getParent();
   return true;
 }
 
+/// \brief Returns true if given declaration is TU-scoped and externally visible
+static bool isDeclTUScopedExternallyVisible(Decl *Decl) {
+  if (auto *FD = dyn_cast<FunctionDecl>(Decl))
+    return (FD->getDeclContext()->isTranslationUnit() || FD->isExternC()) &&
+           FD->hasExternalFormalLinkage();
+  else if (auto *VD = dyn_cast<VarDecl>(Decl))
+    return (VD->getDeclContext()->isTranslationUnit() || VD->isExternC()) &&
+           VD->hasExternalFormalLinkage();
+  else
+    llvm_unreachable("Unknown type of decl!");
+}
+
 NamedDecl *
 Sema::ActOnVariableDeclarator(Scope *S, Declarator &D, DeclContext *DC,
                               TypeSourceInfo *TInfo, LookupResult &Previous,
                               MultiTemplateParamsArg TemplateParamLists,
                               bool &AddToScope) {
   QualType R = TInfo->getType();
   DeclarationName Name = GetNameForDeclarator(D).getName();
 
if (S->getFnParent() != nullptr) {
       if (!R->isIntegralType(Context) && !R->isPointerType()) {
         Diag(D.getLocStart(), diag::err_asm_bad_register_type);
         NewVD->setInvalidDecl(true);
       }
     }
 
     NewVD->addAttr(::new (Context) AsmLabelAttr(SE->getStrTokenLoc(0),
                                                 Context, Label, 0));
-  } else if (!ExtnameUndeclaredIdentifiers.empty()) {
+  } else if (!ExtnameUndeclaredIdentifiers.empty() &&
+             isDeclTUScopedExternallyVisible(NewVD)) {
     llvm::DenseMap<IdentifierInfo*,AsmLabelAttr*>::iterator I =
       ExtnameUndeclaredIdentifiers.find(NewVD->getIdentifier());
     if (I != ExtnameUndeclaredIdentifiers.end()) {
       NewVD->addAttr(I->second);
       ExtnameUndeclaredIdentifiers.erase(I);
     }
   }
 
FilterLookupForScope(Previous, OriginalDC, S, shouldConsiderLinkage(NewFD),
                        isFunctionTemplateSpecialization);
 
   // Handle GNU asm-label extension (encoded as an attribute).
   if (Expr *E = (Expr*) D.getAsmLabel()) {
     // The parser guarantees this is a string.
     StringLiteral *SE = cast<StringLiteral>(E);
     NewFD->addAttr(::new (Context) AsmLabelAttr(SE->getStrTokenLoc(0), Context,
                                                 SE->getString(), 0));
-  } else if (!ExtnameUndeclaredIdentifiers.empty()) {
+  } else if (!ExtnameUndeclaredIdentifiers.empty() &&
+             isDeclTUScopedExternallyVisible(NewFD)) {
     llvm::DenseMap<IdentifierInfo*,AsmLabelAttr*>::iterator I =
       ExtnameUndeclaredIdentifiers.find(NewFD->getIdentifier());
     if (I != ExtnameUndeclaredIdentifiers.end()) {
       NewFD->addAttr(I->second);
       ExtnameUndeclaredIdentifiers.erase(I);
     }
   }
 

test/CodeGen/redefine_extname.c

 // RUN: %clang_cc1 -triple=i386-pc-solaris2.11 -w -emit-llvm %s -o - | FileCheck %s
 
 #pragma redefine_extname fake real
 #pragma redefine_extname name alias
 
 extern int fake(void);
 
 int name;
 
 // __PRAGMA_REDEFINE_EXTNAME should be defined.  This will fail if it isn't...
 int fish() { return fake() + __PRAGMA_REDEFINE_EXTNAME + name; }
 // Check that the call to fake() is emitted as a call to real()
 // CHECK:   call i32 @real()
 // Check that this also works with variables names
 // CHECK:   load i32, i32* @alias
+
+// This is a case when redefenition is deferred *and* we have a local of the
+// same name. PR23923.
+#pragma redefine_extname foo bar
+int f() {
+  int foo = 0;
+  return foo;
+}
+extern int foo() { return 1; }
+// CHECK: define i32 @bar()
+