* [PATCH] tree-optimization/113552 - fix num_call accounting in simd clone vectorization
@ 2024-01-23 11:56 Richard Biener
2024-01-23 12:01 ` Jakub Jelinek
0 siblings, 1 reply; 6+ messages in thread
From: Richard Biener @ 2024-01-23 11:56 UTC (permalink / raw)
To: gcc-patches
The following avoids using exact_log2 on the number of SIMD clone calls
to be emitted when vectorizing calls since that can easily be not
a power of two in which case it will return -1. For different simd
clones the number of calls will differ by a multiply with a power of two
only so using floor_log2 is good enough here.
Bootstrap and regtest running on x86_64-unknown-linux-gnu.
PR tree-optimization/113552
* tree-vect-stmts.cc (vectorizable_simd_clone_call): Use
floor_log2 instead of exact_log2 on the number of calls.
---
gcc/tree-vect-stmts.cc | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/gcc/tree-vect-stmts.cc b/gcc/tree-vect-stmts.cc
index 09749ae3817..1dbe1115da4 100644
--- a/gcc/tree-vect-stmts.cc
+++ b/gcc/tree-vect-stmts.cc
@@ -4071,7 +4071,7 @@ vectorizable_simd_clone_call (vec_info *vinfo, stmt_vec_info stmt_info,
|| (nargs != simd_nargs))
continue;
if (num_calls != 1)
- this_badness += exact_log2 (num_calls) * 4096;
+ this_badness += floor_log2 (num_calls) * 4096;
if (n->simdclone->inbranch)
this_badness += 8192;
int target_badness = targetm.simd_clone.usable (n);
--
2.35.3
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] tree-optimization/113552 - fix num_call accounting in simd clone vectorization
2024-01-23 11:56 [PATCH] tree-optimization/113552 - fix num_call accounting in simd clone vectorization Richard Biener
@ 2024-01-23 12:01 ` Jakub Jelinek
2024-01-23 12:03 ` Richard Biener
0 siblings, 1 reply; 6+ messages in thread
From: Jakub Jelinek @ 2024-01-23 12:01 UTC (permalink / raw)
To: Richard Biener; +Cc: gcc-patches
On Tue, Jan 23, 2024 at 12:56:52PM +0100, Richard Biener wrote:
> The following avoids using exact_log2 on the number of SIMD clone calls
> to be emitted when vectorizing calls since that can easily be not
> a power of two in which case it will return -1. For different simd
> clones the number of calls will differ by a multiply with a power of two
> only so using floor_log2 is good enough here.
>
> Bootstrap and regtest running on x86_64-unknown-linux-gnu.
>
> PR tree-optimization/113552
> * tree-vect-stmts.cc (vectorizable_simd_clone_call): Use
> floor_log2 instead of exact_log2 on the number of calls.
Is there any target which supports non-power-of-two simdlen?
If not, perhaps we should add !pow2p_hwi (num_calls) to the continue;
condition a few lines earlier?
> diff --git a/gcc/tree-vect-stmts.cc b/gcc/tree-vect-stmts.cc
> index 09749ae3817..1dbe1115da4 100644
> --- a/gcc/tree-vect-stmts.cc
> +++ b/gcc/tree-vect-stmts.cc
> @@ -4071,7 +4071,7 @@ vectorizable_simd_clone_call (vec_info *vinfo, stmt_vec_info stmt_info,
> || (nargs != simd_nargs))
> continue;
> if (num_calls != 1)
> - this_badness += exact_log2 (num_calls) * 4096;
> + this_badness += floor_log2 (num_calls) * 4096;
> if (n->simdclone->inbranch)
> this_badness += 8192;
> int target_badness = targetm.simd_clone.usable (n);
> --
> 2.35.3
Jakub
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] tree-optimization/113552 - fix num_call accounting in simd clone vectorization
2024-01-23 12:01 ` Jakub Jelinek
@ 2024-01-23 12:03 ` Richard Biener
2024-01-23 12:21 ` Jakub Jelinek
0 siblings, 1 reply; 6+ messages in thread
From: Richard Biener @ 2024-01-23 12:03 UTC (permalink / raw)
To: Jakub Jelinek; +Cc: gcc-patches
On Tue, 23 Jan 2024, Jakub Jelinek wrote:
> On Tue, Jan 23, 2024 at 12:56:52PM +0100, Richard Biener wrote:
> > The following avoids using exact_log2 on the number of SIMD clone calls
> > to be emitted when vectorizing calls since that can easily be not
> > a power of two in which case it will return -1. For different simd
> > clones the number of calls will differ by a multiply with a power of two
> > only so using floor_log2 is good enough here.
> >
> > Bootstrap and regtest running on x86_64-unknown-linux-gnu.
> >
> > PR tree-optimization/113552
> > * tree-vect-stmts.cc (vectorizable_simd_clone_call): Use
> > floor_log2 instead of exact_log2 on the number of calls.
>
> Is there any target which supports non-power-of-two simdlen?
> If not, perhaps we should add !pow2p_hwi (num_calls) to the continue;
> condition a few lines earlier?
Is non-power-of-two simdlen a thing? Note there's nothing wrong
with non-power-of-two num_calls, with VF == 4 and a group size
of 3 you get 12 lanes and either 3 (simdlen == 4) or 6 (simdlen == 2)
calls.
Iff non-power-of-two simdlen is a thing then we could bias
by + num_calls (no idea why we use *_log2 in the first place, but it
was that way since the beginning).
Richard.
> > diff --git a/gcc/tree-vect-stmts.cc b/gcc/tree-vect-stmts.cc
> > index 09749ae3817..1dbe1115da4 100644
> > --- a/gcc/tree-vect-stmts.cc
> > +++ b/gcc/tree-vect-stmts.cc
> > @@ -4071,7 +4071,7 @@ vectorizable_simd_clone_call (vec_info *vinfo, stmt_vec_info stmt_info,
> > || (nargs != simd_nargs))
> > continue;
> > if (num_calls != 1)
> > - this_badness += exact_log2 (num_calls) * 4096;
> > + this_badness += floor_log2 (num_calls) * 4096;
> > if (n->simdclone->inbranch)
> > this_badness += 8192;
> > int target_badness = targetm.simd_clone.usable (n);
> > --
> > 2.35.3
>
> Jakub
>
>
--
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] tree-optimization/113552 - fix num_call accounting in simd clone vectorization
2024-01-23 12:03 ` Richard Biener
@ 2024-01-23 12:21 ` Jakub Jelinek
2024-01-23 12:40 ` Richard Biener
0 siblings, 1 reply; 6+ messages in thread
From: Jakub Jelinek @ 2024-01-23 12:21 UTC (permalink / raw)
To: Richard Biener; +Cc: gcc-patches
On Tue, Jan 23, 2024 at 01:03:46PM +0100, Richard Biener wrote:
> On Tue, 23 Jan 2024, Jakub Jelinek wrote:
>
> > On Tue, Jan 23, 2024 at 12:56:52PM +0100, Richard Biener wrote:
> > > The following avoids using exact_log2 on the number of SIMD clone calls
> > > to be emitted when vectorizing calls since that can easily be not
> > > a power of two in which case it will return -1. For different simd
> > > clones the number of calls will differ by a multiply with a power of two
> > > only so using floor_log2 is good enough here.
> > >
> > > Bootstrap and regtest running on x86_64-unknown-linux-gnu.
> > >
> > > PR tree-optimization/113552
> > > * tree-vect-stmts.cc (vectorizable_simd_clone_call): Use
> > > floor_log2 instead of exact_log2 on the number of calls.
> >
> > Is there any target which supports non-power-of-two simdlen?
> > If not, perhaps we should add !pow2p_hwi (num_calls) to the continue;
> > condition a few lines earlier?
>
> Is non-power-of-two simdlen a thing? Note there's nothing wrong
> with non-power-of-two num_calls, with VF == 4 and a group size
> of 3 you get 12 lanes and either 3 (simdlen == 4) or 6 (simdlen == 2)
> calls.
>
> Iff non-power-of-two simdlen is a thing then we could bias
> by + num_calls (no idea why we use *_log2 in the first place, but it
> was that way since the beginning).
Ah, with SLP I can understand it doesn't have to be a power of two,
the original
+ if (n->simdclone->simdlen
+ < (unsigned) LOOP_VINFO_VECT_FACTOR (loop_vinfo))
+ this_badness += (exact_log2 (LOOP_VINFO_VECT_FACTOR (loop_vinfo))
+ - exact_log2 (n->simdclone->simdlen)) * 1024;
was written for loop vectorization only and I think correctly assumed
power of 2 loop vectorization factors as well as simdlens.
I admit I don't remember why log2 rather than the count has been used,
the first version of the patch is
https://gcc.gnu.org/pipermail/gcc-patches/2013-November/374728.html
But if we keep using log2, perhaps better ceil_log2 because num_calls of
3 is certainly more expensive than 2.
Jakub
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] tree-optimization/113552 - fix num_call accounting in simd clone vectorization
2024-01-23 12:21 ` Jakub Jelinek
@ 2024-01-23 12:40 ` Richard Biener
2024-01-23 12:43 ` Jakub Jelinek
0 siblings, 1 reply; 6+ messages in thread
From: Richard Biener @ 2024-01-23 12:40 UTC (permalink / raw)
To: Jakub Jelinek; +Cc: gcc-patches
On Tue, 23 Jan 2024, Jakub Jelinek wrote:
> On Tue, Jan 23, 2024 at 01:03:46PM +0100, Richard Biener wrote:
> > On Tue, 23 Jan 2024, Jakub Jelinek wrote:
> >
> > > On Tue, Jan 23, 2024 at 12:56:52PM +0100, Richard Biener wrote:
> > > > The following avoids using exact_log2 on the number of SIMD clone calls
> > > > to be emitted when vectorizing calls since that can easily be not
> > > > a power of two in which case it will return -1. For different simd
> > > > clones the number of calls will differ by a multiply with a power of two
> > > > only so using floor_log2 is good enough here.
> > > >
> > > > Bootstrap and regtest running on x86_64-unknown-linux-gnu.
> > > >
> > > > PR tree-optimization/113552
> > > > * tree-vect-stmts.cc (vectorizable_simd_clone_call): Use
> > > > floor_log2 instead of exact_log2 on the number of calls.
> > >
> > > Is there any target which supports non-power-of-two simdlen?
> > > If not, perhaps we should add !pow2p_hwi (num_calls) to the continue;
> > > condition a few lines earlier?
> >
> > Is non-power-of-two simdlen a thing? Note there's nothing wrong
> > with non-power-of-two num_calls, with VF == 4 and a group size
> > of 3 you get 12 lanes and either 3 (simdlen == 4) or 6 (simdlen == 2)
> > calls.
> >
> > Iff non-power-of-two simdlen is a thing then we could bias
> > by + num_calls (no idea why we use *_log2 in the first place, but it
> > was that way since the beginning).
>
> Ah, with SLP I can understand it doesn't have to be a power of two,
> the original
> + if (n->simdclone->simdlen
> + < (unsigned) LOOP_VINFO_VECT_FACTOR (loop_vinfo))
> + this_badness += (exact_log2 (LOOP_VINFO_VECT_FACTOR (loop_vinfo))
> + - exact_log2 (n->simdclone->simdlen)) * 1024;
> was written for loop vectorization only and I think correctly assumed
> power of 2 loop vectorization factors as well as simdlens.
Note even without SLP we could vectorize a group size of 3 with
interleaving. But yes, VF for interleaving is a power of two and
so is simdlen so the above should have worked.
> I admit I don't remember why log2 rather than the count has been used,
> the first version of the patch is
> https://gcc.gnu.org/pipermail/gcc-patches/2013-November/374728.html
> But if we keep using log2, perhaps better ceil_log2 because num_calls of
> 3 is certainly more expensive than 2.
I think only the relative accounting to the other this_badness
increments matter since as said, at least with power-of-two simdlen
we'd get different {ceil,floor}_log2 values for different simdlen.
It's never going to be 3 vs 2 but 3 * 2^n vs. 3 * 2^m so floor or
ceil doesn't matter. In fact we could have just using
some inverse of exact_log2 (n->simdclone->simdlen). That is,
it's only simdlen that's varying in this addend to this_badness.
For the exact_log2 case the behavior is unchanged and we now only
get a sensible number for the others now. Maybe log2 was for the
fear of overflow or over-accounting compared to the other increments.
When overflow is not an issue we could also use
floor_log2 (num_calls * 4096) to be more "precise". I don't know
why we have all these different weights and why they are the way
they are - but it's a lot of apples and oranges we put together
in a magic number to compare ;)
I prefer to do a minimal change now, but both floor and ceil work
for me, so if you prefer I can change (but as said, it would only
matter with the mixing with the other cost factors, and in unknown
ways since the desire is not spelled out).
Richard.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] tree-optimization/113552 - fix num_call accounting in simd clone vectorization
2024-01-23 12:40 ` Richard Biener
@ 2024-01-23 12:43 ` Jakub Jelinek
0 siblings, 0 replies; 6+ messages in thread
From: Jakub Jelinek @ 2024-01-23 12:43 UTC (permalink / raw)
To: Richard Biener; +Cc: gcc-patches
On Tue, Jan 23, 2024 at 01:40:15PM +0100, Richard Biener wrote:
> It's never going to be 3 vs 2 but 3 * 2^n vs. 3 * 2^m so floor or
> ceil doesn't matter. In fact we could have just using
> some inverse of exact_log2 (n->simdclone->simdlen). That is,
> it's only simdlen that's varying in this addend to this_badness.
>
> For the exact_log2 case the behavior is unchanged and we now only
> get a sensible number for the others now. Maybe log2 was for the
> fear of overflow or over-accounting compared to the other increments.
> When overflow is not an issue we could also use
> floor_log2 (num_calls * 4096) to be more "precise". I don't know
> why we have all these different weights and why they are the way
> they are - but it's a lot of apples and oranges we put together
> in a magic number to compare ;)
>
> I prefer to do a minimal change now, but both floor and ceil work
> for me, so if you prefer I can change (but as said, it would only
> matter with the mixing with the other cost factors, and in unknown
> ways since the desire is not spelled out).
Ok as is then.
Jakub
^ permalink raw reply [flat|nested] 6+ messages in thread
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2024-01-23 11:56 [PATCH] tree-optimization/113552 - fix num_call accounting in simd clone vectorization Richard Biener
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2024-01-23 12:03 ` Richard Biener
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