[clang] [lldb] [clang][DebugInfo] Emit global variable definitions for static data members with constant initializers (PR #70639)

[Greg Clayton via cfe-commits]

clayborg wrote:

> > > Few minor issues, but looks good to me. (you metnioned somewhere an lldb issue I think with this patch when the value is removed from the static member declaration inside the class? If that's a problem - probably hold off on committing this until lldb's been fixed so this doesn't regress things? And document the dependence clearly in the commit message)
> > 
> > 
> > I saw the patch to lldb to test that we can find global variables that are `constexpr`. In upstream, we can't use find global variables, but the expression parser does work for these. We should make sure that both `FindGlobalVariables(...)` and expression parsing work for all `constexpr` globals.
> 
> Yup, the expression evaluator finds them by looking at the `DW_AT_const_value` on the declaration. But since we're moving that constant onto the definition with this patch, that will break that codepath.
> 
> Looking into how best to address that now

The DWARFASTParserClang.cpp will try to create the class from the DWARF for the class definition. You will need to find the `DW_TAG_variable` when we are creating the static field if there is no `DW_AT_const_value` in the `DW_TAG_member`. But we also need to support the `DW_AT_const_value` being in the `DW_TAG_member` since older DWARF will be emitted like this. Are we going to emit a `DW_AT_const_expr` now in the `DW_TAG_member`? If so, then we will know that we need to look for the DW_TAG_variable. I don't think clang emitted the `DW_AT_const_expr` attribute before.

The other option it to just see if the expression parser works since global variables are found correctly. Maybe the same will happen in this case?

https://github.com/llvm/llvm-project/pull/70639