Re: [Bug c/32575] [4.2/4.3 regression] With -ftree-vrp miscompiles a single line of code in SQLite

["Daniel Berlin" <dberlin@dberlin.org>]

On 28 Aug 2007 15:58:29 -0000, jakub at gcc dot gnu dot org
<gcc-bugzilla@gcc.gnu.org> wrote:
>
>
> ------- Comment #6 from jakub at gcc dot gnu dot org  2007-08-28 15:58 -------
> if (a == 0) a = bar (); isn't necessary either.
>
> salias has:
>
>   # BLOCK 2 freq:10000
>   # PRED: ENTRY [100.0%]  (fallthru,exec)
>   # VUSE <qD.2026_12(D), SMT.25D.2079_13(D)> { qD.2026 SMT.25D.2079 }
>   D.2027_3 = foo ();
>   pD.2025_4 = (struct S *) D.2027_3;
>   if (pD.2025_4 == 0B)
>     goto <bb 3>;
>   else
>     goto <bb 4>;
>   # SUCC: 3 [7.3%]  (true,exec) 4 [92.7%]  (false,exec)
>
>   # BLOCK 3 freq:735
>   # PRED: 2 [7.3%]  (true,exec)
>   # qD.2026_15 = VDEF <qD.2026_12(D)>
>   # SMT.25D.2079_16 = VDEF <SMT.25D.2079_13(D)>
>   # SMT.26D.2080_17 = VDEF <SMT.26D.2080_14(D)> { qD.2026 SMT.25D.2079
> SMT.26D.2080 }
>   __builtin_memset (&qD.2026, 0, 24);
>   # SUCC: 4 [100.0%]  (fallthru,exec)
>
>   # BLOCK 4 freq:10000
>   # PRED: 2 [92.7%]  (false,exec) 3 [100.0%]  (fallthru,exec)
>   # qD.2026_11 = PHI <qD.2026_12(D)(2), qD.2026_15(3)>
>   # pD.2025_1 = PHI <pD.2025_4(2), &qD.2026(3)>
>   # qD.2026_18 = VDEF <qD.2026_11> { qD.2026 }
>   pD.2025_1->s1D.2008 = aD.2021_6(D);
>   # qD.2026_19 = VDEF <qD.2026_18> { qD.2026 }
>   pD.2025_1->s2D.2009 = bD.2022_7(D);
>
> Shouldn't the VDEFs be a PHI of some SMT and qD?
For VDEF/VUSE, you will never have a PHI of anything other than
multiple versions of the same SMT/virtual variable.

The above looks right to me at a glance.
It is probably pruning the result using TBAA which is what p->s isn't
thought to access the SMT.