[Bug tree-optimization/51275] CLOBBERS can be optimized if they are right before the return (or RESX)

[matz at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51275

--- Comment #4 from Michael Matz <matz at gcc dot gnu.org> 2011-11-23 14:12:11 UTC ---
Andrew: yes, I considered something similar.  To work really well it requires
some changes to the conflict generation code, though.  Without the clobbers
all objects stay live on the exit-block entry and therefore conflict (and
hence won't be shared).  Conflicts generated only because of the exit block
need to be ignored.

As Jakub says, the implementation should be improved by walking from the exit
block upwards. fab seems like the wrong place to do this.  Something like
DSE feels more natural perhaps.  But it's correct that the removal should
happen after inlining but before eh optimizations.