[PATCH] D141826: [WIP][clang][TemplateBase] Add IsDefaulted bit to TemplateArgument

[Michael Buch via Phabricator via cfe-commits]

Michael137 created this revision.
Michael137 added reviewers: erichkeane, aaron.ballman, dblaikie.
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**Summary**

This patch adds a `IsDefaulted` field to `clang::TemplateArgument`.

To prevent memory footprint increase we still 1 bit from `ArgKind`.

**Background**

In LLDB we construct ASTs from debug-info and hand it to clang
to perform actions such as printing/formatting a typenames.
Some debug formats, specifically DWARF, may only encode information
about class template instantiations, losing the structure of the generic
class definition. However, the `clang::TypePrinter` needs a properly
constructed `ClassTemplateDecl` with generic default argument decls
to be able to deduce whether a `ClassTemplateSpecializationDecl` was
instantiatiated with `TemplateArgument`s that correspond to the
defaults. LLDB does know whether a particular template argument was
defaulted, but can't currently tell clang about it.

This patch allows LLDB to set the defaulted-ness of a `TemplateArgument`
and thus benefit more from `clang::TypePrinter`.

See discussion in https://reviews.llvm.org/D140423

**Testing**

- TODO


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D141826

Files:
  clang/include/clang/AST/TemplateBase.h
  clang/lib/AST/TemplateBase.cpp

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