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

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.

Reviewed By: aprantl

Differential Revision: https://reviews.llvm.org/D94224

clang/include/clang/AST/DeclObjC.h

@@ -656,20 +656,8 @@ public:
 /// \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;
-  };
-
+  /// Location of the left and right angle brackets.
+  SourceRange Brackets;
   /// The number of parameters in the list, which are tail-allocated.
   unsigned NumParams;
 
@@ -717,17 +705,9 @@ public:
     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.

clang/lib/AST/DeclObjC.cpp

@@ -1461,9 +1461,7 @@ SourceRange ObjCTypeParamDecl::getSourceRange() const {
 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());
 }