Re: Help in understanding ccp propagator

["Daniel Berlin" <dberlin at dberlin dot org>]

On 6/3/07, Revital1 Eres <ERES@il.ibm.com> wrote:
> Hello,
>
> I will greatly appreciate any suggestions regarding the following
> problem I have with the ccp propagator. I am testing the new store
> ccp patch which propagates constants by walking the virtual use-def
> chain (http://gcc.gnu.org/ml/gcc-patches/2007-05/msg00055.html) and I
> encountered the following problem while testing tree_join.cc file which
> is under libstdc++-v3 testsuite:


BTW, a lot of these will be caught with the new VN i posted, whicih
should be reviewed and go in soon.
That said, ...

> The final propagator replaces the right operand (D.65705_98) in the
> following if condition with a constant zero which causes the program to be
> aborted as i0_62 is not always zero:
>
>   # i0_62 = PHI <i0_5(29), 0(3)>
> <L139>:;
>   D.61410.first = i0_62;
> ...
>    D.65705_98 = D.61410.first;
> -  if (D.65704_96 >= 0)
> +  if (D.65704_96 >= D.65705_98)
>      goto <bb 11>;
>    else
>      goto <bb 14>;
>
> Tracing the execution of the propagator it seems that the if statement
> is first been propogated with zero after simulating the execution; but not
> updated after the lattice value of the variables it depends on changed.


Does your store CPP properly say the vdefs have changed when a
statement's lattice value changes?

>