[Bug tree-optimization/33572] [4.3 Regression] wrong code with -O

[dnovillo at google dot com]

------- Comment #11 from dnovillo at google dot com  2007-09-30 13:41 -------
Subject: Re:  [4.3 Regression] wrong code with -O

On 30 Sep 2007 12:41:03 -0000, rguenth at gcc dot gnu dot org
<gcc-bugzilla@gcc.gnu.org> wrote:
>
>
> ------- Comment #9 from rguenth at gcc dot gnu dot org  2007-09-30 12:41 -------
> Diego, we seem to have a general problem with the incremental SSA updater.
> If we rename foo$ptr in
>
> <bb 6>:
>   # foo$ptr_16 = PHI <foo$ptr_18(ab)(5), D.1758_3(4)>
>   p_12 = foo$ptr_16;
>   foo$ptr_19(ab) = 0B;
>   p_15 = foo$ptr_16;
>   p_4 = foo$ptr_16;
>   p_5 = foo$ptr_16;
>   D.1781_6 = foo$ptr_16->_vptr.Foo;
>   D.1782_7 = *D.1781_6;
>   OBJ_TYPE_REF(D.1782_7;foo$ptr_16->0) (foo$ptr_16);
>   goto <bb 8>;

Is the symbol foo$ptr being marked for renaming?  If so, that's wrong.
 A gimple register symbol cannot be marked for renaming if there are
overlapping live ranges in its SSA names.  We don't have a general
mechanism to prevent that.  Mostly because we do not keep track when
OLRs are created.  The generic SSA updating mechanism has no cheap way
of checking that.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33572