On Tue, 28 Sep 2021, Richard Biener wrote:
> On Tue, 28 Sep 2021, Hongtao Liu wrote:
>
> > On Tue, Sep 28, 2021 at 2:59 PM Richard Biener via Gcc-patches
> > <gcc-patches@gcc.gnu.org> wrote:
> > >
> > > On Mon, 27 Sep 2021, sunil.k.pandey wrote:
> > >
> > > > On Linux/x86_64,
> > > >
> > > > 6390c5047adb75960f86d56582e6322aaa4d9281 is the first bad commit
> > > > commit 6390c5047adb75960f86d56582e6322aaa4d9281
> > > > Author: Richard Biener <rguent...@suse.de>
> > > > Date: Wed Nov 18 09:36:57 2020 +0100
> > > >
> > > > Allow different vector types for stmt groups
> > > >
> > > > caused
> > > >
> > > > FAIL: gcc.dg/vect/bb-slp-17.c -flto -ffat-lto-objects
> > > > scan-tree-dump-times slp2 "optimized: basic block" 1
> > > > FAIL: gcc.dg/vect/bb-slp-17.c scan-tree-dump-times slp2 "optimized:
> > > > basic block" 1
> > >
> > > This shows that it is maybe a bad idea to support V2SImode vectorization
> > > with -m32 when we refuse to implement even plus.
> > >
> > > OTOH it's just the mode that's available, autovectorize_vector_modes
> > > doesn't include the corresponding mode but we still pick it up via
> > > the related vector mode for group-size == 2.
>
> It looks like we could define the vectorize.related_mode hook to
> reject V2SImode when !TARGET_MMX_WITH_SSE - the default implementation
> just checks for vector_mode_supported_p.
Meh, that doesn't work. We then fall through
else if (SCALAR_INT_MODE_P (prevailing_mode)
|| !related_vector_mode (prevailing_mode,
inner_mode, nunits).exists
(&simd_mode))
{
/* Fall back to using mode_for_vector, mostly in the hope of being
able to use an integer mode. */
if (known_eq (nunits, 0U)
&& !multiple_p (GET_MODE_SIZE (prevailing_mode), nbytes,
&nunits))
return NULL_TREE;
if (!mode_for_vector (inner_mode, nunits).exists (&simd_mode))
return NULL_TREE;
and return V2SImode anyway from mode_for_vector ...
So - should we only allow integer modes here as the comment suggests?
With that, thus
if (!mode_for_vector (inner_mode, nunits).exists (&simd_mode)
|| GET_MODE_CLASS (simd_mode) != MODE_INT)
return NULL_TREE;
we "properly" _not_ use V2SImode for vectorization on x86 when
!TARGET_MMX_WITH_SSE. Note that will also not use V2SImode
for vectorizing copies (which are properly supported). So I'm
not sure rejecting V2SImode outright is "proper" ...
Richard.
