* [PATCH] tree-vect-patterns: One small vect_recog_ctz_ffs_pattern tweak [PR109011]
@ 2023-04-20 17:38 Jakub Jelinek
2023-04-20 17:41 ` Richard Biener
0 siblings, 1 reply; 2+ messages in thread
From: Jakub Jelinek @ 2023-04-20 17:38 UTC (permalink / raw)
To: Richard Biener; +Cc: gcc-patches
Hi!
I've noticed I've made a typo, ifn in this function this late
is always only IFN_CTZ or IFN_FFS, never IFN_CLZ.
Due to this typo, we weren't using the originally intended
.CTZ (X) = .POPCOUNT ((X - 1) & ~X)
but
.CTZ (X) = PREC - .POPCOUNT (X | -X)
instead when we want to emit __builtin_ctz*/.CTZ using .POPCOUNT.
Both compute the same value, both are defined at 0 with the
same value (PREC), both have same number of GIMPLE statements,
but I think the former ought to be preferred, because lots of targets
have andn as a single operation rather than two, and also putting
a -1 constant into a vector register is often cheaper than vector
with broadcast PREC power of two value.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2023-04-20 Jakub Jelinek <jakub@redhat.com>
PR tree-optimization/109011
* tree-vect-patterns.cc (vect_recog_ctz_ffs_pattern): Use
.CTZ (X) = .POPCOUNT ((X - 1) & ~X) in preference to
.CTZ (X) = PREC - .POPCOUNT (X | -X).
--- gcc/tree-vect-patterns.cc.jj 2023-04-20 11:55:03.576154120 +0200
+++ gcc/tree-vect-patterns.cc 2023-04-20 12:09:17.884633795 +0200
@@ -1630,7 +1630,7 @@ vect_recog_ctz_ffs_pattern (vec_info *vi
&& defined_at_zero_new
&& val == prec
&& val_new == prec)
- || (ifnnew == IFN_POPCOUNT && ifn == IFN_CLZ))
+ || (ifnnew == IFN_POPCOUNT && ifn == IFN_CTZ))
{
/* .CTZ (X) = PREC - .CLZ ((X - 1) & ~X)
.CTZ (X) = .POPCOUNT ((X - 1) & ~X). */
Jakub
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH] tree-vect-patterns: One small vect_recog_ctz_ffs_pattern tweak [PR109011]
2023-04-20 17:38 [PATCH] tree-vect-patterns: One small vect_recog_ctz_ffs_pattern tweak [PR109011] Jakub Jelinek
@ 2023-04-20 17:41 ` Richard Biener
0 siblings, 0 replies; 2+ messages in thread
From: Richard Biener @ 2023-04-20 17:41 UTC (permalink / raw)
To: Jakub Jelinek; +Cc: Richard Biener, gcc-patches
> Am 20.04.2023 um 19:40 schrieb Jakub Jelinek via Gcc-patches <gcc-patches@gcc.gnu.org>:
>
> Hi!
>
> I've noticed I've made a typo, ifn in this function this late
> is always only IFN_CTZ or IFN_FFS, never IFN_CLZ.
>
> Due to this typo, we weren't using the originally intended
> .CTZ (X) = .POPCOUNT ((X - 1) & ~X)
> but
> .CTZ (X) = PREC - .POPCOUNT (X | -X)
> instead when we want to emit __builtin_ctz*/.CTZ using .POPCOUNT.
> Both compute the same value, both are defined at 0 with the
> same value (PREC), both have same number of GIMPLE statements,
> but I think the former ought to be preferred, because lots of targets
> have andn as a single operation rather than two, and also putting
> a -1 constant into a vector register is often cheaper than vector
> with broadcast PREC power of two value.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
Ok
> 2023-04-20 Jakub Jelinek <jakub@redhat.com>
>
> PR tree-optimization/109011
> * tree-vect-patterns.cc (vect_recog_ctz_ffs_pattern): Use
> .CTZ (X) = .POPCOUNT ((X - 1) & ~X) in preference to
> .CTZ (X) = PREC - .POPCOUNT (X | -X).
>
> --- gcc/tree-vect-patterns.cc.jj 2023-04-20 11:55:03.576154120 +0200
> +++ gcc/tree-vect-patterns.cc 2023-04-20 12:09:17.884633795 +0200
> @@ -1630,7 +1630,7 @@ vect_recog_ctz_ffs_pattern (vec_info *vi
> && defined_at_zero_new
> && val == prec
> && val_new == prec)
> - || (ifnnew == IFN_POPCOUNT && ifn == IFN_CLZ))
> + || (ifnnew == IFN_POPCOUNT && ifn == IFN_CTZ))
> {
> /* .CTZ (X) = PREC - .CLZ ((X - 1) & ~X)
> .CTZ (X) = .POPCOUNT ((X - 1) & ~X). */
>
> Jakub
>
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