[AST] Remove unnecessary indirections in DeclarationNameTable

DeclarationNameTable currently hold 3 "void *" to
FoldingSet<CXXSpecialName>, FoldingSet<CXXLiteralOperatorIdName>
and FoldingSet<CXXDeductionGuideNameExtra>.

CXXSpecialName, CXXLiteralOperatorIdName and
CXXDeductionGuideNameExtra are private classes holding extra
information about a "special" declaration name and are in
AST/DeclarationName.cpp. The original intent seems to have
been to keep these classes private and only expose
DeclarationNameExtra and DeclarationName (the code dates from
2008 and has not been significantly changed since).

However this make the code less straightforward than necessary
because of the need to have "void *" in DeclarationNameTable
(with 1 of 3 comments wrong) and to manually allocate/deallocate
the FoldingSets.

Moreover removing the extra indirections reduce the run-time of
an fsyntax-only on all of Boost by 2.3% which is not totally
unexpected given how frequently this data structure is used
(especially for C++).

A concern raised by erichkeane during the review was that
including Type.h would increase the compile time unreasonably.
However test builds (both clean and incremental) showed that
this patch did not result in any compile time increase.

Reviewed By: erichkeane

Differential Revision: https://reviews.llvm.org/D50261

llvm-svn: 339030

0 files changed, 0 insertions, 0 deletions