r226436 - Sema: Variable definitions cannot be __attribute__((alias))
David Majnemer
david.majnemer at gmail.com
Tue Jan 20 17:26:26 PST 2015
On Tue, Jan 20, 2015 at 4:15 PM, Richard Smith <richard at metafoo.co.uk>
wrote:
> On Mon, Jan 19, 2015 at 1:00 AM, David Majnemer
> <david.majnemer at gmail.com> wrote:
> > Author: majnemer
> > Date: Mon Jan 19 03:00:28 2015
> > New Revision: 226436
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=226436&view=rev
> > Log:
> > Sema: Variable definitions cannot be __attribute__((alias))
> >
> > Things that are OK:
> > extern int var1 __attribute((alias("v1")));
> > static int var2 __attribute((alias("v2")));
>
> This seems surprising; it looks like there are two definitions of var2
> here (one from the alias and the other from the variable definition).
> I don't see that this is different from var3.
>
I agree, GCC singles these out as being fine though.
>
> > Things that are not OK:
> > int var3 __attribute((alias("v3")));
> > extern int var4 __attribute((alias("v4"))) = 4;
>
> Is this OK:
>
> const int var6 __attribute__((alias("v6")));
>
I assume this is -x c? GCC rejects this.
>
> It implicitly has internal linkage, and adding 'extern' to it would
> change semantics, but it looks more like var3 than var2.
>
> > We choose to accpet:
> > struct S { static int var5 __attribute((alias("v5"))); };
> >
> > This code causes assertion failues in GCC 4.8 and ICC 13.0.1, we have
> > no reason to reject it.
> >
> > This partially fixes PR22217.
> >
> > Modified:
> > cfe/trunk/include/clang/Basic/Attr.td
> > cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
> > cfe/trunk/lib/Sema/SemaDecl.cpp
> > cfe/trunk/lib/Sema/SemaDeclAttr.cpp
> > cfe/trunk/test/Misc/ast-dump-attr.cpp
> > cfe/trunk/test/Sema/alias-redefinition.c
> >
> > Modified: cfe/trunk/include/clang/Basic/Attr.td
> > URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/Attr.td?rev=226436&r1=226435&r2=226436&view=diff
> >
> ==============================================================================
> > --- cfe/trunk/include/clang/Basic/Attr.td (original)
> > +++ cfe/trunk/include/clang/Basic/Attr.td Mon Jan 19 03:00:28 2015
> > @@ -345,6 +345,8 @@ def AddressSpace : TypeAttr {
> > def Alias : Attr {
> > let Spellings = [GCC<"alias">];
> > let Args = [StringArgument<"Aliasee">];
> > + let Subjects = SubjectList<[Function, GlobalVar], ErrorDiag,
> > +
> "ExpectedFunctionGlobalVarMethodOrProperty">;
> > let Documentation = [Undocumented];
> > }
> >
> >
> > Modified: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
> > URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?rev=226436&r1=226435&r2=226436&view=diff
> >
> ==============================================================================
> > --- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td (original)
> > +++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td Mon Jan 19
> 03:00:28 2015
> > @@ -3902,10 +3902,8 @@ def warn_missing_variable_declarations :
> > def err_static_data_member_reinitialization :
> > Error<"static data member %0 already has an initializer">;
> > def err_redefinition : Error<"redefinition of %0">;
> > -def err_alias_after_tentative :
> > - Error<"alias definition of %0 after tentative definition">;
> > -def err_tentative_after_alias :
> > - Error<"tentative definition of %0 after alias definition">;
> > +def err_alias_is_definition :
> > + Error<"definition %0 cannot also be an alias">;
> > def err_definition_of_implicitly_declared_member : Error<
> > "definition of implicitly declared %select{default constructor|copy "
> > "constructor|move constructor|copy assignment operator|move
> assignment "
> >
> > Modified: cfe/trunk/lib/Sema/SemaDecl.cpp
> > URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDecl.cpp?rev=226436&r1=226435&r2=226436&view=diff
> >
> ==============================================================================
> > --- cfe/trunk/lib/Sema/SemaDecl.cpp (original)
> > +++ cfe/trunk/lib/Sema/SemaDecl.cpp Mon Jan 19 03:00:28 2015
> > @@ -2219,18 +2219,8 @@ static void checkNewAttributesAfterDef(S
> > const Attr *NewAttribute = NewAttributes[I];
> >
> > if (isa<AliasAttr>(NewAttribute)) {
> > - if (FunctionDecl *FD = dyn_cast<FunctionDecl>(New))
> > - S.CheckForFunctionRedefinition(FD, cast<FunctionDecl>(Def));
> > - else {
> > - VarDecl *VD = cast<VarDecl>(New);
> > - unsigned Diag =
> cast<VarDecl>(Def)->isThisDeclarationADefinition() ==
> > - VarDecl::TentativeDefinition
> > - ? diag::err_alias_after_tentative
> > - : diag::err_redefinition;
> > - S.Diag(VD->getLocation(), Diag) << VD->getDeclName();
> > - S.Diag(Def->getLocation(), diag::note_previous_definition);
> > - VD->setInvalidDecl();
> > - }
> > + FunctionDecl *FD = cast<FunctionDecl>(New);
> > + S.CheckForFunctionRedefinition(FD, cast<FunctionDecl>(Def));
> > ++I;
> > continue;
> > }
> > @@ -5103,6 +5093,18 @@ static void checkAttributesAfterMerging(
> > if (ND.isExternallyVisible()) {
> > S.Diag(Attr->getLocation(),
> diag::err_attribute_weakref_not_static);
> > ND.dropAttr<WeakRefAttr>();
> > + ND.dropAttr<AliasAttr>();
> > + }
> > + }
> > +
> > + if (auto *VD = dyn_cast<VarDecl>(&ND)) {
> > + if (VD->hasInit()) {
> > + if (const auto *Attr = VD->getAttr<AliasAttr>()) {
> > + assert(VD->isThisDeclarationADefinition() &&
> > + !VD->isExternallyVisible() && "Broken AliasAttr handled
> late!");
> > + S.Diag(Attr->getLocation(), diag::err_alias_is_definition) <<
> VD;
> > + VD->dropAttr<AliasAttr>();
> > + }
> > }
> > }
> >
> > @@ -9617,18 +9619,6 @@ Sema::FinalizeDeclaration(Decl *ThisDecl
> > }
> > }
> >
> > - if (!VD->isInvalidDecl() &&
> > - VD->isThisDeclarationADefinition() ==
> VarDecl::TentativeDefinition) {
> > - if (const VarDecl *Def = VD->getDefinition()) {
> > - if (Def->hasAttr<AliasAttr>()) {
> > - Diag(VD->getLocation(), diag::err_tentative_after_alias)
> > - << VD->getDeclName();
> > - Diag(Def->getLocation(), diag::note_previous_definition);
> > - VD->setInvalidDecl();
> > - }
> > - }
> > - }
> > -
> > const DeclContext *DC = VD->getDeclContext();
> > // If there's a #pragma GCC visibility in scope, and this isn't a
> class
> > // member, set the visibility of this variable.
> >
> > Modified: cfe/trunk/lib/Sema/SemaDeclAttr.cpp
> > URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDeclAttr.cpp?rev=226436&r1=226435&r2=226436&view=diff
> >
> ==============================================================================
> > --- cfe/trunk/lib/Sema/SemaDeclAttr.cpp (original)
> > +++ cfe/trunk/lib/Sema/SemaDeclAttr.cpp Mon Jan 19 03:00:28 2015
> > @@ -1492,6 +1492,20 @@ static void handleAliasAttr(Sema &S, Dec
> > return;
> > }
> >
> > + // Aliases should be on declarations, not definitions.
> > + if (const auto *FD = dyn_cast<FunctionDecl>(D)) {
> > + if (FD->isThisDeclarationADefinition()) {
> > + S.Diag(Attr.getLoc(), diag::err_alias_is_definition) << FD;
> > + return;
> > + }
> > + } else {
> > + const auto *VD = cast<VarDecl>(D);
> > + if (VD->isThisDeclarationADefinition() &&
> VD->isExternallyVisible()) {
> > + S.Diag(Attr.getLoc(), diag::err_alias_is_definition) << VD;
> > + return;
> > + }
> > + }
> > +
> > // FIXME: check if target symbol exists in current file
> >
> > D->addAttr(::new (S.Context) AliasAttr(Attr.getRange(), S.Context,
> Str,
> >
> > Modified: cfe/trunk/test/Misc/ast-dump-attr.cpp
> > URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Misc/ast-dump-attr.cpp?rev=226436&r1=226435&r2=226436&view=diff
> >
> ==============================================================================
> > --- cfe/trunk/test/Misc/ast-dump-attr.cpp (original)
> > +++ cfe/trunk/test/Misc/ast-dump-attr.cpp Mon Jan 19 03:00:28 2015
> > @@ -79,7 +79,7 @@ void TestInt(void) __attribute__((constr
> > // CHECK: FunctionDecl{{.*}}TestInt
> > // CHECK-NEXT: ConstructorAttr{{.*}} 123
> >
> > -int TestString __attribute__((alias("alias1")));
> > +static int TestString __attribute__((alias("alias1")));
> > // CHECK: VarDecl{{.*}}TestString
> > // CHECK-NEXT: AliasAttr{{.*}} "alias1"
> >
> >
> > Modified: cfe/trunk/test/Sema/alias-redefinition.c
> > URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/alias-redefinition.c?rev=226436&r1=226435&r2=226436&view=diff
> >
> ==============================================================================
> > --- cfe/trunk/test/Sema/alias-redefinition.c (original)
> > +++ cfe/trunk/test/Sema/alias-redefinition.c Mon Jan 19 03:00:28 2015
> > @@ -23,22 +23,5 @@ void fun4(void);
> > void f5() {}
> > void __attribute((alias("f5"))) fun5(void) {} // expected-error
> {{redefinition of 'fun5'}} // expected-note {{previous definition}}
> >
> > -int v1;
> > -int var1 __attribute((alias("v1"))); // expected-note {{previous
> definition}}
> > -int var1 __attribute((alias("v1"))); // expected-error {{redefinition
> of 'var1'}}
> > -
> > -int v2;
> > -int var2 = 2; // expected-note {{previous definition}}
> > -int var2 __attribute((alias("v2"))); // expected-error {{redefinition
> of 'var2'}}
> > -
> > -int v3;
> > -int var3 __attribute((alias("v3"))); // expected-note {{previous
> definition}}
> > -int var3 = 2; // expected-error {{redefinition of 'var3'}}
> > -
> > -int v4;
> > -int var4; // expected-note {{previous definition}}
> > -int var4 __attribute((alias("v4"))); // expected-error {{alias
> definition of 'var4' after tentative definition}}
> > -
> > -int v5;
> > -int var5 __attribute((alias("v5"))); // expected-note {{previous
> definition}}
> > -int var5; // expected-error {{tentative definition of 'var5' after
> alias definition}}
>
> Might it be useful to keep these testcases (and mark the definitions
> with the alias attribute as as 'extern' to restore the former behavior
> of the tests)?
>
> > +int var1 __attribute((alias("v1"))); // expected-error {{definition
> 'var1' cannot also be an alias}}
> > +static int var2 __attribute((alias("v2"))) = 2; // expected-error
> {{definition 'var2' cannot also be an alias}}
> >
> >
> > _______________________________________________
> > cfe-commits mailing list
> > cfe-commits at cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
>
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