[Bug driver/69451] New: want a high-level option to disable optimizations that harm debuggability

[richlowe at richlowe dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69451

            Bug ID: 69451
           Summary: want a high-level option to disable optimizations that
                    harm debuggability
           Product: gcc
           Version: 5.3.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: driver
          Assignee: unassigned at gcc dot gnu.org
          Reporter: richlowe at richlowe dot net
                CC: alan.coopersmith at oracle dot com
  Target Milestone: ---

There are several optimization passes in the compiler which make debugging,
tracing, and the like, unnecessarily cumbersome.

The big and obvious examples that spring to mind are optimizations that clone
functions and Identical Code Folding (which does the opposite).  Each makes
tracing, placing breakpoints, etc, error prone and frustrating.  A lot of
optimization passes in question are indeed documented in this regard.

It would be fantastic to have a high-level option which disabled optimizations
which harm debugging in this way, so that users have a reliable way to do so
without researching any optimization in each new release.

I would suggest that any optimization which:

  - Changed the number or order of parameters
  - Passed parameters in a way other than defined by the relevant ABI
  - Cloned a function such that a logical function had more than one copy in
text, with gensym'd names.
  - ICF'd a function such that a logical function had no copy in text, but was
instead aliased to another

Should be disabled by the desired flag.