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

[Michael Buch via cfe-commits]

Michael137 wrote:

> > That's true, if defined in a header, we'll emit a DW_TAG_variable for the constant in each compile unit the header is included in. GCC does do the right thing and only emit the definition DIE in a single CU. We should probably do the same. Though not sure at which level we want to catch that.
> 
> Which variable are you discussing here, `val1` or `val2`?
> 
> For `val1`, we could not emit the constant value and only emit the real definition (there's /some/ risk here - non-ODR uses (or otherwise optimized away uses) of the variable may mean that the object file that defines the variable won't be linked in - so we'd miss the constant value) For `val2` the variable is effectively `inline` and doesn't have a home, so there's no one place that we can emit the `DW_TAG_variable` out-of-line definition...

Sorry for the confusion. I wasn't referring to that code snippet.

Also, I must've not looked at the GCC dwarfdump output carefully enough. Compiling two CUs that include a class with a `static constexpr` member will produce two separate definitions and two entries in `.debug_pubnames`:
```
.debug_pubnames                                                                                            
global die-in-sect 0x00000070, cu-in-sect 0x0000000c, die-in-cu 0x00000070, cu-header-in-sect 0x00000000 'Foo::val2'                                                                                                   
global die-in-sect 0x0000007b, cu-in-sect 0x0000000c, die-in-cu 0x0000007b, cu-header-in-sect 0x00000000 'main'                                                                                                       
global die-in-sect 0x00000118, cu-in-sect 0x000000b4, die-in-cu 0x00000070, cu-header-in-sect 0x000000a8 'Foo::val2'                                                                                                   
global die-in-sect 0x00000128, cu-in-sect 0x000000b4, die-in-cu 0x00000080, cu-header-in-sect 0x000000a8 'Foo::func'               
```

So to answer Greg's question, yes we will potentially produce multiple variable definition DIEs. One for each CU that the header was included in

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