[Clang][AST] Move NamespaceDecl bits to DeclContext (#98567)

Currently, `NamespaceDecl` has a member `AnonOrFirstNamespaceAndFlags`
which stores a few pieces of data:
- a bit indicating whether the namespace was declared `inline`, and
- a bit indicating whether the namespace was declared as a
_nested-namespace-definition_, and
- a pointer a `NamespaceDecl` that either stores:
- a pointer to the first declaration of that namespace if the
declaration is no the first declaration, or
- a pointer to the unnamed namespace that inhabits the namespace
otherwise.

`Redeclarable` already stores a pointer to the first declaration of an
entity, so it's unnecessary to store this in `NamespaceDecl`.
`DeclContext` has 8 bytes in which various bitfields can be stored for a
declaration, so it's not necessary to store these in `NamespaceDecl`
either. We only need to store a pointer to the unnamed namespace that
inhabits the first declaration of a namespace. This patch moves the two
bits currently stored in `NamespaceDecl` to `DeclContext`, and only
stores a pointer to the unnamed namespace that inhabits a namespace in
the first declaration of that namespace. Since `getOriginalNamespace`
always returns the same `NamespaceDecl` as `getFirstDecl`, this function
is removed to avoid confusion.

1 files changed, 1 insertions, 2 deletions

diff --git a/clang/lib/AST/DeclBase.cpp b/clang/lib/AST/DeclBase.cpp
index ef2c57e..bc5a920 100644
--- a/clang/lib/AST/DeclBase.cpp
+++ b/clang/lib/AST/DeclBase.cpp
@@ -1422,8 +1422,7 @@ DeclContext *DeclContext::getPrimaryContext() {
   case Decl::TranslationUnit:
     return static_cast<TranslationUnitDecl *>(this)->getFirstDecl();
   case Decl::Namespace:
-    // The original namespace is our primary context.
-    return static_cast<NamespaceDecl *>(this)->getOriginalNamespace();
+    return static_cast<NamespaceDecl *>(this)->getFirstDecl();
 
   case Decl::ObjCMethod:
     return this;