r323528 - [AST] Use bit packing to reduce sizeof(TypedefNameDecl) from 88 to 80.

[Vlad Tsyrklevich via cfe-commits]

This change has broken a number of buildbots, e.g.
http://lab.llvm.org:8011/builders/sanitizer-windows/builds/23163

On Fri, Jan 26, 2018 at 6:15 AM Benjamin Kramer via cfe-commits <
cfe-commits at lists.llvm.org> wrote:

> Author: d0k
> Date: Fri Jan 26 06:14:11 2018
> New Revision: 323528
>
> URL: http://llvm.org/viewvc/llvm-project?rev=323528&view=rev
> Log:
> [AST] Use bit packing to reduce sizeof(TypedefNameDecl) from 88 to 80.
>
> We can stash the cached transparent tag bit in existing pointer padding.
> Everything coming out of ASTContext is always aligned to a multiple of
> 8, so we have 8 spare bits.
>
> Modified:
>     cfe/trunk/include/clang/AST/Decl.h
>     cfe/trunk/lib/AST/Decl.cpp
>
> Modified: cfe/trunk/include/clang/AST/Decl.h
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/AST/Decl.h?rev=323528&r1=323527&r2=323528&view=diff
>
> ==============================================================================
> --- cfe/trunk/include/clang/AST/Decl.h (original)
> +++ cfe/trunk/include/clang/AST/Decl.h Fri Jan 26 06:14:11 2018
> @@ -2814,12 +2814,12 @@ public:
>  /// Base class for declarations which introduce a typedef-name.
>  class TypedefNameDecl : public TypeDecl, public
> Redeclarable<TypedefNameDecl> {
>    using ModedTInfo = std::pair<TypeSourceInfo *, QualType>;
> -  llvm::PointerUnion<TypeSourceInfo *, ModedTInfo *> MaybeModedTInfo;
>
> -  // FIXME: This can be packed into the bitfields in Decl.
> -  /// If 0, we have not computed IsTransparentTag.
> -  /// Otherwise, IsTransparentTag is (CacheIsTransparentTag >> 1).
> -  mutable unsigned CacheIsTransparentTag : 2;
> +  /// If int part is 0, we have not computed IsTransparentTag.
> +  /// Otherwise, IsTransparentTag is (getInt() >> 1).
> +  mutable llvm::PointerIntPair<
> +      llvm::PointerUnion<TypeSourceInfo *, ModedTInfo *>, 2>
> +      MaybeModedTInfo;
>
>    void anchor() override;
>
> @@ -2828,7 +2828,7 @@ protected:
>                    SourceLocation StartLoc, SourceLocation IdLoc,
>                    IdentifierInfo *Id, TypeSourceInfo *TInfo)
>        : TypeDecl(DK, DC, IdLoc, Id, StartLoc), redeclarable_base(C),
> -        MaybeModedTInfo(TInfo), CacheIsTransparentTag(0) {}
> +        MaybeModedTInfo(TInfo, 0) {}
>
>    using redeclarable_base = Redeclarable<TypedefNameDecl>;
>
> @@ -2855,26 +2855,29 @@ public:
>    using redeclarable_base::getMostRecentDecl;
>    using redeclarable_base::isFirstDecl;
>
> -  bool isModed() const { return MaybeModedTInfo.is<ModedTInfo*>(); }
> +  bool isModed() const {
> +    return MaybeModedTInfo.getPointer().is<ModedTInfo *>();
> +  }
>
>    TypeSourceInfo *getTypeSourceInfo() const {
> -    return isModed()
> -      ? MaybeModedTInfo.get<ModedTInfo*>()->first
> -      : MaybeModedTInfo.get<TypeSourceInfo*>();
> +    return isModed() ? MaybeModedTInfo.getPointer().get<ModedTInfo
> *>()->first
> +                     : MaybeModedTInfo.getPointer().get<TypeSourceInfo
> *>();
>    }
>
>    QualType getUnderlyingType() const {
> -    return isModed()
> -      ? MaybeModedTInfo.get<ModedTInfo*>()->second
> -      : MaybeModedTInfo.get<TypeSourceInfo*>()->getType();
> +    return isModed() ? MaybeModedTInfo.getPointer().get<ModedTInfo
> *>()->second
> +                     : MaybeModedTInfo.getPointer()
> +                           .get<TypeSourceInfo *>()
> +                           ->getType();
>    }
>
>    void setTypeSourceInfo(TypeSourceInfo *newType) {
> -    MaybeModedTInfo = newType;
> +    MaybeModedTInfo.setPointer(newType);
>    }
>
>    void setModedTypeSourceInfo(TypeSourceInfo *unmodedTSI, QualType
> modedTy) {
> -    MaybeModedTInfo = new (getASTContext()) ModedTInfo(unmodedTSI,
> modedTy);
> +    MaybeModedTInfo.setPointer(new (getASTContext(), 8)
> +                                   ModedTInfo(unmodedTSI, modedTy));
>    }
>
>    /// Retrieves the canonical declaration of this typedef-name.
> @@ -2891,8 +2894,8 @@ public:
>    /// Determines if this typedef shares a name and spelling location with
> its
>    /// underlying tag type, as is the case with the NS_ENUM macro.
>    bool isTransparentTag() const {
> -    if (CacheIsTransparentTag)
> -      return CacheIsTransparentTag & 0x2;
> +    if (MaybeModedTInfo.getInt())
> +      return MaybeModedTInfo.getInt() & 0x2;
>      return isTransparentTagSlow();
>    }
>
>
> Modified: cfe/trunk/lib/AST/Decl.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/Decl.cpp?rev=323528&r1=323527&r2=323528&view=diff
>
> ==============================================================================
> --- cfe/trunk/lib/AST/Decl.cpp (original)
> +++ cfe/trunk/lib/AST/Decl.cpp Fri Jan 26 06:14:11 2018
> @@ -4372,9 +4372,7 @@ bool TypedefNameDecl::isTransparentTagSl
>    };
>
>    bool isTransparent = determineIsTransparent();
> -  CacheIsTransparentTag = 1;
> -  if (isTransparent)
> -    CacheIsTransparentTag |= 0x2;
> +  MaybeModedTInfo.setInt((isTransparent << 1) | 1);
>    return isTransparent;
>  }
>
>
>
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