On Wed, Nov 16, 2022 at 04:30:06PM +0100, Richard Biener via Gcc-patches wrote:
> On Wed, Nov 16, 2022 at 4:29 PM Richard Biener
> <richard.guent...@gmail.com> wrote:
> >
> > On Wed, Nov 16, 2022 at 4:25 PM Tamar Christina <tamar.christ...@arm.com>
> > wrote:
> > >
> > > Hi,
> > >
> > > This patch is causing several ICEs because it changes the permutes from a
> > > single register
> > > permute to a multi register due to the lowering of the expressions to
> > > different SSA names.
> > >
> > > See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107717
> > >
> > > I have a prototype fix which adds a new rule to CSE this back to a single
> > > register permute,
> > > but would this be the right solution? It seems hard to later on during
> > > expand realize that
> > > the two operands are the same.
> > >
> > > It's probably also ok to just block this from happening after vec_lower,
> > > however I'm worried that
> > > If it wasn't CSE'd before vec_lower it'll lower it so something much less
> > > efficient.
> >
> > You can use
> >
> > (vec_perm (op@7 @0 @1) @3)
>
> Err, (vec_perm (op@7 @0 @1) @7) obviously.
Even:
--- gcc/match.pd.jj 2022-11-15 07:56:05.240348804 +0100
+++ gcc/match.pd 2022-11-16 16:35:34.854080956 +0100
@@ -8259,7 +8259,7 @@ and,
(simplify
(op (vec_perm @0 @0 @2) (vec_perm @1 @1 @2))
(if (VECTOR_INTEGER_TYPE_P (type))
- (vec_perm (op @0 @1) (op @0 @1) @2))))
+ (vec_perm (op@3 @0 @1) @3 @2))))
/* Similar for float arithmetic when permutation constant covers
all vector elements. */
@@ -8298,4 +8298,4 @@ and,
}
}
(if (full_perm_p)
- (vec_perm (op @0 @1) (op @0 @1) @2))))))
+ (vec_perm (op@3 @0 @1) @3 @2))))))
>From quick look at the dumps, it seems to work fine.
Jakub
