On Mon, Oct 11, 2021 at 10:23 AM Kewen.Lin via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Hi Hongtao,
>
> on 2021/10/11 上午10:10, liuhongt via Gcc-patches wrote:
> > libgomp/ChangeLog:
> >
> > * testsuite/libgomp.graphite/force-parallel-8.c: Add
> > -fno-tree-vectorize.
> > ---
> > libgomp/testsuite/libgomp.graphite/force-parallel-8.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/libgomp/testsuite/libgomp.graphite/force-parallel-8.c
> > b/libgomp/testsuite/libgomp.graphite/force-parallel-8.c
> > index f9e07039172..0f3d138cebd 100644
> > --- a/libgomp/testsuite/libgomp.graphite/force-parallel-8.c
> > +++ b/libgomp/testsuite/libgomp.graphite/force-parallel-8.c
> > @@ -1,4 +1,4 @@
> > -/* { dg-additional-options "-fdisable-tree-thread1
> > -fdisable-tree-vrp-thread1" } */
> > +/* { dg-additional-options "-fdisable-tree-thread1
> > -fdisable-tree-vrp-thread1 -fno-tree-vectorize" } */
> >
> > #define N 1500
> >
> >
>
> Thanks for doing this!
>
> This issue was observed in rs6000 specific PR102658 as well.
>
> I've looked into it a bit, it's caused by the "conditional store replacement"
> which
> is originally disabled without vectorization as below code.
>
> /* If either vectorization or if-conversion is disabled then do
> not sink any stores. */
> if (param_max_stores_to_sink == 0
> || (!flag_tree_loop_vectorize && !flag_tree_slp_vectorize)
> || !flag_tree_loop_if_convert)
> return false;
>
> The new change makes the innermost loop look like
>
> for (int c1 = 0; c1 <= 1499; c1 += 1) {
> if (c1 <= 500) {
> S_10(c0, c1);
> } else {
> S_9(c0, c1);
> }
> S_11(c0, c1);
> }
>
> and can not be splitted as:
>
> for (int c1 = 0; c1 <= 500; c1 += 1)
> S_10(c0, c1);
>
> for (int c1 = 501; c1 <= 1499; c1 += 1)
> S_9(c0, c1);
>
> So instead of disabling vectorization, could we just disable this cs
> replacement
> with parameter "--param max-stores-to-sink=0"?
>
> I tested this proposal on ppc64le, it should work as well.
>
> What do you think of it?
I can confirm it also works for x86, I'll adjust the patch.
Thank you for the analysis.
>
> BR,
> Kewen
--
BR,
Hongtao
