http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48830
Hans-Peter Nilsson <hp at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|[4.4/4.6 Regression] |[4.4/4.5/4.6/4.7
|unrecognized insn storing |Regression] unrecognized
|fp (simd) reg in SImode to |insn: storing invalid upper
|stack |fp reg in SImode to stack
--- Comment #3 from Hans-Peter Nilsson <hp at gcc dot gnu.org> 2011-05-01
00:31:15 UTC ---
I had a look. The code needs to split %f34 and get the two SImode quantities
that happen to be in %f34. This should be done by a stack intermediate, but
when doing that, reloads trips and falls.
The root problem seems to be that the SPARC port allows a change from DImode to
SImode for regno 66 (%f34) (by CANNOT_CHANGE_MODE_CLASS) even though there's no
%f35 and no way to move around such a small quantity, also specified through
HARD_REGNO_MODE_OK(either of 66 and 67, SImode) being 0. So, reload happily
wraps the reg in a subreg and calls emit_move_insn.
It seems wrong for the sparc CANNOT_CHANGE_MODE_CLASS to not refuse this
change, but also wrong for subreg_get_info to not consult HARD_REGNO_MODE_OK
when setting info.representable_p (as "%f35" is flagged as representable, which
it isn't according to the related field comment in rtl.h). There's a kludge
involving the latter, that implies that such a non-representable register is
expected to be flagged as representable (ugh!), see last "return -1" in
simplify_subreg_regno.
