r226436 - Sema: Variable definitions cannot be __attribute__((alias))
Richard Smith
richard at metafoo.co.uk
Tue Jan 20 17:36:29 PST 2015
On Tue, Jan 20, 2015 at 5:26 PM, David Majnemer
<david.majnemer at gmail.com> wrote:
> 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.
This is -x c++, so that the 'const' implies internal linkage, and
adding 'extern' would be incorrect.
OK, after playing with GCC a bit, I think this is just a bug on their
end. They accept this nonsense, for instance:
extern const int v6 = 456;
const int var6 = 123;
int k = var6;
extern const int var6 __attribute__((alias("v6")));
... and initialize k to 123. I think they're just completely failing
to check for a preceding definition. I don't think it makes sense to
be bug-compatible with 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}}
>> >
>> >
>> > _______________________________________________
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>> > cfe-commits at cs.uiuc.edu
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>
>
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