[clang][ASTContext] Call setAttached for comments attached to a declaration

[jkorous]

Summary

I believe this is a bug affecting performance when compiling with -Wdocumentation.
In Sema::ActOnDocumentable we're checking whether there are any comments unattached to declaration at the end of comment list whenever we encounter new documentable declaration.
Since this property of RawComment was never set we were trying to find comments every time and that involves at least a couple expensive SourceLocation decompositions.

[gribozavr]

Good catch!

clang/lib/AST/ASTContext.cpp

258 ↗

(On Diff #198089)

(*Comment)->setAttached(); (for consistency with the rest of the code).

300 ↗

(On Diff #198089)

(*Comment)->setAttached(); (for consistency with the rest of the code).

cfe/trunk/lib/AST/ASTContext.cpp

if (Comment != RawComments.end() &&
     std::pair<FileID, unsigned> CommentBeginDecomp
       = SourceMgr.getDecomposedLoc((*Comment)->getSourceRange().getBegin());
     // Check that Doxygen trailing comment comes after the declaration, starts
     // on the same line and in the same file as the declaration.
     if (DeclLocDecomp.first == CommentBeginDecomp.first &&
         SourceMgr.getLineNumber(DeclLocDecomp.first, DeclLocDecomp.second)
           == SourceMgr.getLineNumber(CommentBeginDecomp.first,
                                      CommentBeginDecomp.second)) {
+      (**Comment).setAttached();
       return *Comment;
     }
   }
 
   // The comment just after the declaration was not a trailing comment.
   // Let's look at the previous comment.
   if (Comment == RawComments.begin())
     return nullptr;
#endif
   StringRef Text(Buffer + CommentEndDecomp.second,
                  DeclLocDecomp.second - CommentEndDecomp.second);
 
   // There should be no other declarations or preprocessor directives between
   // comment and declaration.
   if (Text.find_first_of(";{}#@") != StringRef::npos)
     return nullptr;
 
+  (**Comment).setAttached();
   return *Comment;
 }
 
 /// If we have a 'templated' declaration for a template, adjust 'D' to
 /// refer to the actual template.
 /// If we have an implicit instantiation, adjust 'D' to refer to template.
 static const Decl *adjustDeclToTemplate(const Decl *D) {
   if (const auto *FD = dyn_cast<FunctionDecl>(D)) {