[clang] [NFC] [Serializer] Pack information in serializer (PR #69287)

[Chuanqi Xu via cfe-commits]

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@@ -617,24 +617,27 @@ void ASTDeclReader::VisitDecl(Decl *D) {
                            Reader.getContext());
   }
   D->setLocation(ThisDeclLoc);
-  D->InvalidDecl = Record.readInt();
-  if (Record.readInt()) { // hasAttrs
+
+  uint64_t DeclBits = Record.readInt();
+  D->InvalidDecl = DeclBits & 0x1;
+  D->setImplicit(DeclBits & (1 << 2));
+  D->Used = (DeclBits >> 3) & 0x1;
+  IsDeclMarkedUsed |= D->Used;
+  D->setReferenced(DeclBits & (1 << 4));
+  D->setTopLevelDeclInObjCContainer(DeclBits & (1 << 5));
+  D->setAccess((AccessSpecifier)((DeclBits >> 6) & 0x3));
+  D->FromASTFile = true;
+  auto ModuleOwnership = (Decl::ModuleOwnershipKind)((DeclBits >> 8) & 0x7);
----------------
ChuanqiXu9 wrote:

Yes... and I feel the magic numbers for some types (e.g., `AccessSpecifier` and `ModuleOwnershipKind`) might not be so scaring. Since the devs can see `AccessSpecifier` and `ModuleOwnershipKind` here then they can get the size quickly. Also even if now we have to look at both ASTWriterDecl.cpp and ASTReaderDecl.cpp to change anything. I mean, it is already tightly bounded.

https://github.com/llvm/llvm-project/pull/69287