------- Comment #8 from rguenth at gcc dot gnu dot org 2010-02-13 10:11 -------
(In reply to comment #3)
> Basically yet another example of why it is a REALLY BAD IDEA to use constants
> as PHI arguments. If the constant from "s =0" would not be propagated into the
> PHI, the statement would not be dead and removed, and no new "s=0" would have
> to be inserted in the wrong place.
>
> See bug 42906 for another example of exactly the same problem.
>
> Allowing constants as PHI arguments is GCC's biggest design f*ck-up.
I'm not sure - do other compilers usually not allow this? It shouldn't be
hard to at least disable propagation of constants into PHIs (there may be
a number of optimizers generating PHIs with constants initially though).
Note that I also see
<bb 4>:
# s_1 = PHI <s_6(3)>
again and again - shouldn't these be plain assignments as well? Thus,
should blocks with a single predecessor have PHIs at all?
I suppose with the insertion at the wrong place you mean
<bb 3>:
# i_2 = PHI <0(2)>
# s_11 = PHI <0(2)>
as done by the pre-header generated by loop init? (they are
dead anyway, but re-generated all the time)
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rguenth at gcc dot gnu dot
| |org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42839
