RFC on discourse:
https://discourse.llvm.org/t/rfc-debug-info-for-coroutine-suspension-locations-take-2/86606
With this commit, we add `DILabel` debug infos to the resume points of a
coroutine. Those labels can be used by debugging scripts to figure out
the exact line and column at which a coroutine was suspended by looking
up current `__coro_index` value inside the coroutines frame, and then
searching for the corresponding label inside the coroutine's resume
function.
The DWARF information generated for such a label looks like:
```
0x00000f71: DW_TAG_label
DW_AT_name ("__coro_resume_1")
DW_AT_decl_file ("generator-example.cpp")
DW_AT_decl_line (5)
DW_AT_decl_column (3)
DW_AT_artificial (true)
DW_AT_LLVM_coro_suspend_idx (0x01)
DW_AT_low_pc (0x00000000000019be)
```
The labels can be mapped to their corresponding `__coro_idx` values
either via their naming convention `__coro_resume_<N>` or using the new
`DW_AT_LLVM_coro_suspend_idx` attribute. In gdb, those line numebrs can
be looked up using `info line -function my_coroutine -label
__coro_resume_1`. LLDB unfortunately does not understand DW_TAG_label
debug information, yet.
Given this is an artificial compiler-generated label, I did apply the
DW_AT_artificial tag to it. The DWARFv5 standard only allows that tag on
type and variable definitions, but this is a natural extension and was
also blessed in the RFC on discourse.
Also, this commit adds `DW_AT_decl_column` to labels, not only for
coroutines but also for normal C and C++ labels. While not strictly
necessary, I am doing so now because it would be harder to do so later
without breaking the binary LLVM-IR format
Drive-by fixes: While reading the existing test cases to understand how
to write my own test case, I did a couple of small typo fixes and
comment improvements
de3c8410d8