Re: [PATCH] MATCH: first of the value replacement moving from phiopt

[Andrew Pinski via Gcc-patches]

On Wed, Aug 2, 2023 at 11:10 PM Jeff Law via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
>
>
> On 8/2/23 17:52, Andrew Pinski via Gcc-patches wrote:
> > This moves a few simple patterns that are done in value replacement
> > in phiopt over to match.pd. Just the simple ones which might show up
> > in other code.
> >
> > This allows some optimizations to happen even without depending
> > on sinking from happening and in some cases where phiopt is not
> > invoked (cond-1.c is an example there).
> >
> > OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.
> >
> > gcc/ChangeLog:
> >
> >       * match.pd (`a == 0 ? b : b + a`,
> >       `a == 0 ? b : b - a`): New patterns.
> >
> > gcc/testsuite/ChangeLog:
> >
> >       * gcc.dg/tree-ssa/cond-1.c: New test.
> >       * gcc.dg/tree-ssa/phi-opt-33.c: New test.
> >       * gcc.dg/tree-ssa/phi-opt-34.c: New test.
> Are you going to remove the old implementation from phiopt?

That is the plan but I doubt it will be completed for GCC 14 because
it will require a lot of changes to the match-and-simplify part of
phi-opt to support all of what value replacement does and I have not
thought through what is fully required to do that yet.
I know having multiple things in the partial state is not a good idea
but in this case other passes benefit from this change as shown by the
cond-1.c testcase, loop if-conv also uses match-and-simplify when
creating its conditional expressions (since r13-263-g9801ca737b1dcb;
well it uses generic fold since r0-118636-gf35613b29cb159) so that
pass will benefit in this case, removing the conditional even.

I have a few other patches to remove many parts of minmax of phiopt
that I will finish up for GCC 14 though so at least there will be more
code removed from phi-opt for GCC 14.

Thanks,
Andrew

PS here is a testcase where the vectorized code is improved due to this patch:
```
int f(unsigned *a, unsigned *b, unsigned *c, unsigned *d)
{
        for(int i = 0;i < 128; i++)
        {
                unsigned aa = a[i];
                unsigned bb = b[i];
                unsigned cc = c[i];
                unsigned r;
                unsigned r1;
                if (aa == 0)
                {
                  r = bb;
                  r1 = 1;
                } else {
                   r = bb+aa;
                   r1 = 0;
                }
                c[i] = r;
                d[i] = r1;
        }
}
```

>
> Jeff