Re: [PATCH] Reset source location for instructions moved out of its original residing basic block

[Ian Lance Taylor <iant@google.com>]

On Thu, Nov 1, 2012 at 10:00 AM, Dehao Chen <dehao@google.com> wrote:
>
> I see your point. How about we guard these changes with a flag, say
> -gless-jumpy, so that people can always choose between better coverage
> and less jumpy gdb behavior (it's also important for some other
> clients like AutoFDO). I will have a series of patches to follow soon
> that can be guarded by this flag.

This feels to me like an attempt to address the problem in the wrong
place.  It seems to me that it would be better to do one of:

* Use -Og and ensure that -Og does not move the code around.
Presumably this would lead to worse runtime performance and better
performance in the debugger.

* Add heuristics to the debugger to jump around less.

* Add a new debug facility to mark the statement as attached to a
particular source location, but moved relative to other source
locations.  Add facilities to the debugger to take that into account.

That said, I suppose I can imagine a mode like you suggest.  It
shouldn't be a -g option, it should be a -f option, like
-fdiscard-moved-insn-debug-locations or something.  That would be
along the lines of -fno-var-tracking: we generate worse debug info
upon user request.

Ian