r226653 - AST: Don't ignore alignas on EnumDecls when calculating alignment

[Justin Bogner]

David Majnemer <david.majnemer at gmail.com> writes:
> Author: majnemer
> Date: Wed Jan 21 04:54:38 2015
> New Revision: 226653
>
> URL: http://llvm.org/viewvc/llvm-project?rev=226653&view=rev
> Log:
> AST: Don't ignore alignas on EnumDecls when calculating alignment
>
> We didn't consider any alignment attributes on an EnumDecl when
> calculating alignment.
>
> While we are here, ignore alignment specifications on typedef types if
> one is used as the underlying type.  Otherwise, weird things happen:
>
> enum Y : int;
> Y y;
>
> typedef int __attribute__((aligned(64))) u;
> enum Y : u {};
>
> What is the alignment of 'Y'?  It would be more consistent with the
> overall design of enums with fixed underlying types to consider the
> underlying type's UnqualifiedDesugaredType.

Is it more consistent? What about the case without the forward
declaration, or if the forward declaration also specifies the alignment?
It's not really clear what the programmer's intent is in these cases
anyway, maybe we could warn that they seem to be doing something silly?

> This fixes PR22279.
>
> Modified:
>     cfe/trunk/lib/AST/ASTContext.cpp
>     cfe/trunk/lib/Sema/SemaDeclAttr.cpp
>     cfe/trunk/test/CXX/dcl.dcl/dcl.attr/dcl.align/p5.cpp
>     cfe/trunk/test/Sema/align-x86.c
>
> Modified: cfe/trunk/lib/AST/ASTContext.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/ASTContext.cpp?rev=226653&r1=226652&r2=226653&view=diff
> ==============================================================================
> --- cfe/trunk/lib/AST/ASTContext.cpp (original)
> +++ cfe/trunk/lib/AST/ASTContext.cpp Wed Jan 21 04:54:38 2015
> @@ -1670,8 +1670,16 @@ TypeInfo ASTContext::getTypeInfoImpl(con
>        break;
>      }
>  
> -    if (const EnumType *ET = dyn_cast<EnumType>(TT))
> -      return getTypeInfo(ET->getDecl()->getIntegerType());
> +    if (const EnumType *ET = dyn_cast<EnumType>(TT)) {
> +      const EnumDecl *ED = ET->getDecl();
> +      TypeInfo Info =
> +          getTypeInfo(ED->getIntegerType()->getUnqualifiedDesugaredType());
> +      if (unsigned AttrAlign = ED->getMaxAlignment()) {
> +        Info.Align = AttrAlign;
> +        Info.AlignIsRequired = true;
> +      }
> +      return Info;
> +    }
>  
>      const RecordType *RT = cast<RecordType>(TT);
>      const ASTRecordLayout &Layout = getASTRecordLayout(RT->getDecl());
> @@ -1786,6 +1794,8 @@ unsigned ASTContext::getPreferredTypeAli
>    T = T->getBaseElementTypeUnsafe();
>    if (const ComplexType *CT = T->getAs<ComplexType>())
>      T = CT->getElementType().getTypePtr();
> +  if (const EnumType *ET = T->getAs<EnumType>())
> +    T = ET->getDecl()->getIntegerType().getTypePtr();
>    if (T->isSpecificBuiltinType(BuiltinType::Double) ||
>        T->isSpecificBuiltinType(BuiltinType::LongLong) ||
>        T->isSpecificBuiltinType(BuiltinType::ULongLong))
>
> Modified: cfe/trunk/lib/Sema/SemaDeclAttr.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDeclAttr.cpp?rev=226653&r1=226652&r2=226653&view=diff
> ==============================================================================
> --- cfe/trunk/lib/Sema/SemaDeclAttr.cpp (original)
> +++ cfe/trunk/lib/Sema/SemaDeclAttr.cpp Wed Jan 21 04:54:38 2015
> @@ -2953,12 +2953,15 @@ void Sema::AddAlignedAttr(SourceRange At
>  void Sema::CheckAlignasUnderalignment(Decl *D) {
>    assert(D->hasAttrs() && "no attributes on decl");
>  
> -  QualType Ty;
> -  if (ValueDecl *VD = dyn_cast<ValueDecl>(D))
> -    Ty = VD->getType();
> -  else
> -    Ty = Context.getTagDeclType(cast<TagDecl>(D));
> -  if (Ty->isDependentType() || Ty->isIncompleteType())
> +  QualType UnderlyingTy, DiagTy;
> +  if (ValueDecl *VD = dyn_cast<ValueDecl>(D)) {
> +    UnderlyingTy = DiagTy = VD->getType();
> +  } else {
> +    UnderlyingTy = DiagTy = Context.getTagDeclType(cast<TagDecl>(D));
> +    if (EnumDecl *ED = dyn_cast<EnumDecl>(D))
> +      UnderlyingTy = ED->getIntegerType();
> +  }
> +  if (DiagTy->isDependentType() || DiagTy->isIncompleteType())
>      return;
>  
>    // C++11 [dcl.align]p5, C11 6.7.5/4:
> @@ -2977,10 +2980,10 @@ void Sema::CheckAlignasUnderalignment(De
>  
>    if (AlignasAttr && Align) {
>      CharUnits RequestedAlign = Context.toCharUnitsFromBits(Align);
> -    CharUnits NaturalAlign = Context.getTypeAlignInChars(Ty);
> +    CharUnits NaturalAlign = Context.getTypeAlignInChars(UnderlyingTy);
>      if (NaturalAlign > RequestedAlign)
>        Diag(AlignasAttr->getLocation(), diag::err_alignas_underaligned)
> -        << Ty << (unsigned)NaturalAlign.getQuantity();
> +        << DiagTy << (unsigned)NaturalAlign.getQuantity();
>    }
>  }
>  
>
> Modified: cfe/trunk/test/CXX/dcl.dcl/dcl.attr/dcl.align/p5.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CXX/dcl.dcl/dcl.attr/dcl.align/p5.cpp?rev=226653&r1=226652&r2=226653&view=diff
> ==============================================================================
> --- cfe/trunk/test/CXX/dcl.dcl/dcl.attr/dcl.align/p5.cpp (original)
> +++ cfe/trunk/test/CXX/dcl.dcl/dcl.attr/dcl.align/p5.cpp Wed Jan 21 04:54:38 2015
> @@ -15,6 +15,12 @@ enum alignas(1) E1 {}; // expected-error
>  enum alignas(1) E2 : char {}; // ok
>  enum alignas(4) E3 { e3 = 0 }; // ok
>  enum alignas(4) E4 { e4 = 1ull << 33 }; // expected-error {{requested alignment is less than minimum alignment of 8 for type 'E4'}}
> +enum alignas(8) E5 {};
> +static_assert(alignof(E5) == 8, "");
> +
> +typedef __attribute__((aligned(16))) int IntAlign16;
> +enum E6 : IntAlign16 {};
> +static_assert(alignof(E6) == 4, "");
>  
>  struct S1 {
>    alignas(8) int n;
>
> Modified: cfe/trunk/test/Sema/align-x86.c
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/align-x86.c?rev=226653&r1=226652&r2=226653&view=diff
> ==============================================================================
> --- cfe/trunk/test/Sema/align-x86.c (original)
> +++ cfe/trunk/test/Sema/align-x86.c Wed Jan 21 04:54:38 2015
> @@ -27,6 +27,8 @@ double g6[3];
>  short chk1[__alignof__(g6) == 8 ? 1 : -1];
>  short chk2[__alignof__(double[3]) == 8 ? 1 : -1];
>  
> +enum { x = 18446744073709551615ULL } g7;
> +short chk1[__alignof__(g7) == 8 ? 1 : -1];
>  
>  // PR5637
>  
>
>
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