[clang][AST] Get rid of an alignment hack in DeclObjC.h [NFCI]

[miyuki]

Summary

This code currently uses a union object to increase the
alignment of the type ObjCTypeParamList. The original intent of this
trick was to be able to use the expression this + 1 to access the
beginning of a tail-allocated array of ObjCTypeParamDecl * pointers.

The code has since been refactored and uses llvm::TrailingObjects to
manage the tail-allocated array. This template takes care of
alignment, so the hack is no longer necessary.

This patch removes the union so that the SourceRange class can be
used directly instead of being re-implemented with raw representations
of source locations.

[miyuki]

Fixed formatting.

[aprantl]

clang/include/clang/AST/DeclObjC.h

660

Can you add a comment here explaining why the alignas is needed here? It's not obvious from the context.

[miyuki]

Removed alignas

[miyuki]

clang/include/clang/AST/DeclObjC.h

660

Actually, alignas is not needed here. I've removed it and updated the commit message to explain why.

[aprantl]

That's even better!

clang/include/clang/AST/DeclObjC.h

 /// or a category/extension thereof.
 ///
 /// \code
 /// @interface NSArray<T> // stores the <T>
 /// @end
 /// \endcode
 class ObjCTypeParamList final
     : private llvm::TrailingObjects<ObjCTypeParamList, ObjCTypeParamDecl *> {
-  /// Stores the components of a SourceRange as a POD.
-  struct PODSourceRange {
-    unsigned Begin;
-    unsigned End;
-  };
-
-  union {
-    /// Location of the left and right angle brackets.
-    PODSourceRange Brackets;
-
-    // Used only for alignment.
-    ObjCTypeParamDecl *AlignmentHack;
-  };
-
+  SourceRange Brackets;
   /// The number of parameters in the list, which are tail-allocated.
   unsigned NumParams;
 
   ObjCTypeParamList(SourceLocation lAngleLoc,
                     ArrayRef<ObjCTypeParamDecl *> typeParams,
                     SourceLocation rAngleLoc);
 
 public:
ObjCTypeParamDecl *front() const {
     return *begin();
   }
 
   ObjCTypeParamDecl *back() const {
     assert(size() > 0 && "empty Objective-C type parameter list");
     return *(end() - 1);
   }
 
-  SourceLocation getLAngleLoc() const {
-    return SourceLocation::getFromRawEncoding(Brackets.Begin);
-  }
-
-  SourceLocation getRAngleLoc() const {
-    return SourceLocation::getFromRawEncoding(Brackets.End);
-  }
-
-  SourceRange getSourceRange() const {
-    return SourceRange(getLAngleLoc(), getRAngleLoc());
-  }
+  SourceLocation getLAngleLoc() const { return Brackets.getBegin(); }
+  SourceLocation getRAngleLoc() const { return Brackets.getEnd(); }
+  SourceRange getSourceRange() const { return Brackets; }
 
   /// Gather the default set of type arguments to be substituted for
   /// these type parameters when dealing with an unspecialized type.
   void gatherDefaultTypeArgs(SmallVectorImpl<QualType> &typeArgs) const;
 };
 
 enum class ObjCPropertyQueryKind : uint8_t {
   OBJC_PR_query_unknown = 0x00,

clang/lib/AST/DeclObjC.cpp

 }
 
 //===----------------------------------------------------------------------===//
 // ObjCTypeParamList
 //===----------------------------------------------------------------------===//
 ObjCTypeParamList::ObjCTypeParamList(SourceLocation lAngleLoc,
                                      ArrayRef<ObjCTypeParamDecl *> typeParams,
                                      SourceLocation rAngleLoc)
-    : NumParams(typeParams.size()) {
-  Brackets.Begin = lAngleLoc.getRawEncoding();
-  Brackets.End = rAngleLoc.getRawEncoding();
+    : Brackets(lAngleLoc, rAngleLoc), NumParams(typeParams.size()) {
   std::copy(typeParams.begin(), typeParams.end(), begin());
 }
 
 ObjCTypeParamList *ObjCTypeParamList::create(
                      ASTContext &ctx,
                      SourceLocation lAngleLoc,
                      ArrayRef<ObjCTypeParamDecl *> typeParams,
                      SourceLocation rAngleLoc) {