Re: Help in understanding ccp propagator

[Revital1 Eres <ERES at il dot ibm dot com>]

> > 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.

Thanks, should it handle cases like the one in the following example -
http://gcc.gnu.org/ml/gcc-patches/2007-03/txt00081.txt?  I tried it with
the VN patch but it seems to not caught it...

> > 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?

I am not sure I understand.  The new patch uses the infrastructure of
the propagator and I do not see an indication in the dumps for vdefs
update after the lattice value is changed:

19930
19931 Visiting statement:
19932 D.61410.first = i0_62;
19933
19934 Lattice value changed to CONSTANT 0.  Adding SSA edges to worklist.
19935

Thanks again fo your help,
Revital