[Bug c++/43486] Preserve variable-use locations

[dmalcolm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43486

--- Comment #12 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
(In reply to David Malcolm from comment #11)
> Author: dmalcolm
> Date: Wed Jan 10 19:40:55 2018
> New Revision: 256448
> 
> URL: https://gcc.gnu.org/viewcvs?rev=256448&root=gcc&view=rev
> Log:
> Preserving locations for variable-uses and constants (PR c++/43486)

This patch is a step towards fixing this bug, but we're not there yet:

The patch adds machinery for adding location wrapper nodes for those
expressions that don't have them, and adds such wrappers to the C++ FE for
callsite arguments and at a few other places. This is a minimal approach, which
improves various diagnostics in the C++ FE, but in theory we should add
wrappers throughout the C++ FE for *all* uses-of-decls and uses-of-constants. 
See:
  https://gcc.gnu.org/ml/gcc-patches/2017-11/msg01588.html
for an earlier work-in-progress attempt at this (probably bit-rotted by now).

Similarly, the patch doesn't add any wrapper nodes to other frontends, in
particular, the C FE.

Finally, I believe, all of these wrappers are discarded at some point at or
before gimplification, so it doesn't help the middle-end yet; we'd need some
way to retain the location information there.