This was originally added in https://reviews.llvm.org/D142268 to have
LLDB display variable typenames that benefit from suppressing defaulted
template arguments.
We currently represent template aliases as `DW_AT_typedef`s instead of
`DW_TAG_template_alias`. This means for types like:
```
template <class _Tp>
using __remove_cv_t = __remove_cv(_Tp);
template <class _Tp>
using remove_cv_t = __remove_cv_t<_Tp>;
template<typename T>
class optional {
using value_type = T;
remove_cv_t<value_type> __val_;
}
```
we would generate DWARF like:
```
0x0000274f: DW_TAG_typedef
DW_AT_type (0x0000000000002758 "__remove_cv_t<value_type>")
DW_AT_name ("remove_cv_t<value_type>")
```
This is an actual libc++ type layout introduced in
https://github.com/llvm/llvm-project/pull/110355, and uncovered a
shortcoming of LLDB's data-formatter infrastructure, where we cache
formatters on the contents of `DW_AT_name` (which currently wouldn't be
a fully resolved typename for template specializations).
To unblock the libc++ change, I think we can revert this without much
fallout.
Then we have two options for follow-up (or do both):
1. reland this but adjust the LLDB formatter cache so it doesn't cache
formatters for template specializations
2. implement support for `DW_TAG_template_alias` in LLDB (and make Clang
generate them by default).
Fix issue https://github.com/llvm/llvm-project/issues/54624
Add front end flags -gtemplate-alias (also a cc1 flag) and -gno-template-alias
to enable/disable usage of the feature. It's enabled by default in the front
end for SCE debugger tuning only.
GCC emits DW_TAG_typedef for template aliases (as does Clang with this feature
disabled), and GDB and LLDB appear not to support DW_TAG_template_alias.
The -Xclang option -gsimple-template-names=mangled is treated the same as
=full, which is not a regression from current behaviour for template
aliases.
The current implementation omits defaulted arguments and as a consequence
also omits empty parameter packs that come after defaulted arguments. Again,
this isn't a regression as the DW_TAG_typedef name doesn't contain defaulted
arguments.
LLVM support added in https://github.com/llvm/llvm-project/pull/88943
Added template-alias.cpp - Check the metadata construction & interaction with
-gsimple-template-names.
Added variadic-template-alias.cpp - Check template parameter packs work.
Added defaulted-template-alias.cpp - Check defaulted args (don't) work.
Modified debug-options.c - Check Clang generates correct cc1 flags.
**Summary**
This patch customizes the `CGDebugInfo` printing policy to stop canonicalizing
the template arugment list in `DW_AT_name` for alias templates. The motivation for
this is that we want to be able to use the `TypePrinter`s support for
omitting defaulted template arguments when emitting `DW_AT_name`.
For reference, GCC currently completely omits the template arguments
when emitting alias template DIEs.
**Testing**
* Added unit-test
Differential Revision: https://reviews.llvm.org/D142268
LLVM r236120 renamed debug info IR constructs to use a `DI` prefix, now
that the `DIDescriptor` hierarchy has been gone for about a week. This
commit was generated using the rename-md-di-nodes.sh upgrade script
attached to PR23080, followed by running clang-format-diff.py on the
`lib/` portion of the patch.
llvm-svn: 236121
This reverts commit r218917, effectively reapplying r218913. Original
commit message follows.
--
Update debug info testcases for an LLVM metadata schema change to fold
metadata constant operands into a single `MDString`.
Part of PR17891.
llvm-svn: 219011
Update debug info testcases for an LLVM metadata schema change to fold
metadata constant operands into a single `MDString`.
Part of PR17891.
llvm-svn: 218913
To simplify source location offsets, this test uses line directives to
force particular lines of interest to have known line numbers so that
adjustments before/after those points don't require updates to the CHECK
lines.
llvm-svn: 207779
We already got the type alias correct (though I've included a test case
here) since Clang represents that like any other typedef - but type
alias templates weren't being handled.
llvm-svn: 205691
