http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52573
Alexandre Oliva <aoliva at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2012-12-07
CC| |aoliva at gcc dot gnu.org,
| |zadeck at naturalbridge dot
| |com
Ever Confirmed|0 |1
--- Comment #5 from Alexandre Oliva <aoliva at gcc dot gnu.org> 2012-12-07
00:14:12 UTC ---
I've looked a bit into this. The code in df-problems.c (see bug 32749) is at
least inconsistent. df_note_bb_compute is supposed to set do_not_gen at the
def, so that we emit the REG_UNUSED but not the REG_DEAD. However, it does not
set do_not_gen for clobbers (may or must), even though it emits the note. Oh,
and it only emits the note if it's not a call;for calls, the REG_UNUSED note is
not emitted for clobbers (I wonder why that is), and we still fail to set
do_not_gen, so we emit the REG_DEAD for the parallel use anyway.
Kenny, it seems to me that we should set do_not_gen regardless of any clobber
flags, because the whole (documented) point of do_not_gen is to avoid emitting
a REG_DEAD for a parallel use, and we should make the REG_UNUSED note emission
consistently conditional on clobbers. Does it sound like this would work?
