[Bug debug/47590] pragma optimize doesn't recompute derived options (was: var tracking produces wrong debug in code where optimization is turned off using pragma)

[aoliva at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47590

Alexandre Oliva <aoliva at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|aoliva at gcc dot gnu.org   |unassigned at gcc dot
                   |                            |gnu.org
            Summary|var tracking produces wrong |pragma optimize doesn't
                   |debug in code where         |recompute derived options
                   |optimization is turned off  |(was: var tracking produces
                   |using pragma                |wrong debug in code where
                   |                            |optimization is turned off
                   |                            |using pragma)

--- Comment #9 from Alexandre Oliva <aoliva at gcc dot gnu.org> 2012-03-25 11:22:19 UTC ---
Sorry, closing e bug was a mistake. The only thing I fixed was the ability to
override -fvar-tracking with #pragma optimize, so that the change is taken into
acount on all targets.  We don't seem to have infrastructure to recompute flags
whose defaults are implied from others after #pragma optimize, and I haven't
even tried to implement that.  I just made sure that, if that is ever
implemented, the recomputed values will be used on all targets.  Meanwhile, add
“, "-fno-var-tracking", "-fno-var-tracking-assignments"” to the #pragma line,
and you'll get the intended behavior.

Incidentally, the inability to recompute implied flags, check inconsistencies,
etc, requires both options to be provided, and if any function compiled with
VTA enabled is inlined into one with these overriders, gcc will crash because
the VTA note will survive all the way to final.  There is code that forces
flag_var_tracking into a special clean-up mode when VTA is enabled when
var-tracking isn't, but that code doesn't get a chance to run after #pragma
optimize.

I'm unassigning this bug, in the hope that someone can take over from here.