After this patch, in the following snippet:
```
template <typename T> Foo {};
template <template <typename T> class CT = Foo> Bar {};
Bar<> b;
```
The debug-info entry for the `CT` template parameter will have
a `DW_AT_default_value (true)` attached to it.
Differential Revision: https://reviews.llvm.org/D139989
DWARFv5 added support for labelling template parameters with
DW_AT_default_value to indicate whether the particular instantiation
defaulted parameter. The current implementation only supports a limited
set of possible cases. Namely for non-value-dependent integral template
parameters and simple type template parameters.
Useful cases that don't work are:
1. Type template parameters with defaults that are
themselves templates. E.g.,
```
template<typename T1, typename T2 = Foo<T1>> class C1;
template<typename T = Foo<int>> class C2;
etc.
```
2. Template template parameters
`clang::isSubstitutedDefaultArgument` already implement the required logic
to determine whether a template argument is defaulted. This patch re-uses
this logic for DWARF CodeGen.
Differential Revision: https://reviews.llvm.org/D139988
**Summary**
Starting with DWARFv5, DW_AT_default_value can be used to indicate
that a template argument has a default value. With this patch LLVM
will emit the this attribute earlier versions of DWARF, unless
compiling with -gstrict-dwarf.
Differential Revision: https://reviews.llvm.org/D139953
**Summary**
Starting with DWARFv5, DW_AT_default_value can be used to indicate
that a template argument has a default value. With this patch Clang
will attach the attribute to the debug metadata regardless of version.
In a follow-up patch we will change llvm to emit this attribute in
earlier versions of DWARF, unless compiling with -gstrict-dwarf.
**Details**
* Previously the DwarfVersion check in CGDebugInfo was inconsistent:
For non-type template arguments we attached the attribute to the debug
metadata in DWARFv5 only. Whereas for type template arguments we didn't
have such a version restriction. With this patch we attach the attribute
regardless of DWARF version (and instead offload the check to the AsmPrinter
in a future patch).
This addresses the immediate bug, though in theory we could still
produce a default parameter for the DWARF in this test case - but other
cases will be definitely unachievable (you could have a default
parameter that cannot be evaluated - so long as the user overrode it
with another value rather than relying on that default)
Caused an assertion due to mismatched bit widths - this seems like the
right API to use for a possibly width-varying equality test. Though
certainly open to some post-commit review feedback if there's a more
suitable way to do this comparison/test.
This patch adds support for dwarf emission/dumping part of debuginfo
generation for defaulted parameters.
Reviewers: probinson, aprantl, dblaikie
Reviewed By: aprantl, dblaikie
Differential Revision: https://reviews.llvm.org/D73462
