[Bug debug/60805] New: Validate const expressions created by var-tracking / debug information across targets.

[ramana at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60805

            Bug ID: 60805
           Summary: Validate const expressions created by var-tracking /
                    debug information across targets.
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ramana at gcc dot gnu.org

While fixing PR60655 Jakub noted that the problem really was that var-tracking
and debug info generation can play a bit fast and loose in the types of
expressions that are generated. Particularly the problem is when const
expressions involving sym_refs are created, targets need to be able to handle /
given a chance to decide on what kinds of expressions are valid and what not. 

Additionally const_ok_for_output_1 and friends in dwarf2out.c don't necessarily
have the entire information on this and require some guess work in this.

For 4.10 we need to instrument the compiler to produce some traces of the
typical kinds of debug expressions that are generated, for a variety of targets
and attempt to handle these in a common manner and only allow the basic common
subset and possibly allowing targets to enable further constants to be
generated.