[Bug tree-optimization/29680] Misscompilation of spec2006 gcc

["dberlin at dberlin dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #6 from dberlin at gcc dot gnu dot org  2006-11-01 17:53 -------
Subject: Re:  Misscompilation of spec2006 gcc

> > >
> > > and for_clobber is only true on call operands, we do not insert SMT.  The lists
> > > of virtual operands thus become disjoint.
> > We should not insert the SMT here.
> > We are never supposed to use a bare SMT when it has aliases that we
> > can use (IE something has not been pruned).
>
> but fde_13->dw_fde_cfi does not have any other aliases that can be used,
> i.e., none_added is true.

This is only true for one of the accesses, not both, or else the SMT
would be used in both cases. :)

>
> > I will work around this problem by teaching PTA about casts from
> > nonpointers to pointers, which will cause it to end up with a nonlocal
> > var in the set.
>
> ??? There is no cast from non-pointer to pointer in this testcase.

Actually, there is.
That's why you end up with SMT's in the first place.
  #   VUSE <fde_table_in_useD.1609_6>;
  fde_table_in_use.0D.1617_7 = fde_table_in_useD.1609;
  D.1618_8 = fde_table_in_use.0D.1617_7 * 24;
  D.1619_9 = (struct dw_fde_struct *) D.1618_8;

This causes D.1619_9 to point to anything

  #   VUSE <fde_tableD.1610_10>;
  fde_table.1D.1620_11 = fde_tableD.1610;
  D.1621_12 = D.1619_9 + fde_table.1D.1620_11;

causes D.1621_12 (the &fde_table[fde_table_in_use - 1]) to point to anything.

All of this is what causes SMT's to be used.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29680