* [PATCH AARCH64] One-line tidy of bit-twiddle expression in aarch64.c
@ 2014-04-23 15:29 Alan Lawrence
2014-04-29 12:48 ` Richard Earnshaw
0 siblings, 1 reply; 4+ messages in thread
From: Alan Lawrence @ 2014-04-23 15:29 UTC (permalink / raw)
To: gcc-patches
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This patch is a small tidy of a more-complicated expression that just flips a
single bit and can thus be a simple XOR.
No regressions on aarch64-none-elf or aarch64_be-none-elf. (I've verified code
is indeed exercised by dg-torture.exp vshuf-v*.c).
Also ok after applying TBL and testsuite patches in
http://gcc.gnu.org/ml/gcc-patches/2014-04/msg01309.html and
http://gcc.gnu.org/ml/gcc-patches/2014-04/msg00579.html.
gcc/ChangeLog:
2014-04-23 Alan Lawrence <alan.lawrence@arm.com>
* config/aarch64/aarch64.c (aarch64_expand_vec_perm_1): tidy bit-flip expression.
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diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index a3147ee..b879754 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -8124,7 +8124,7 @@ aarch64_expand_vec_perm_const_1 (struct expand_vec_perm_d *d)
rtx x;
for (i = 0; i < nelt; ++i)
- d->perm[i] = (d->perm[i] + nelt) & (2 * nelt - 1);
+ d->perm[i] ^= nelt; /* Keep the same index, but in the other vector. */
x = d->op0;
d->op0 = d->op1;
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH AARCH64] One-line tidy of bit-twiddle expression in aarch64.c
2014-04-23 15:29 [PATCH AARCH64] One-line tidy of bit-twiddle expression in aarch64.c Alan Lawrence
@ 2014-04-29 12:48 ` Richard Earnshaw
2014-04-29 18:56 ` Richard Henderson
0 siblings, 1 reply; 4+ messages in thread
From: Richard Earnshaw @ 2014-04-29 12:48 UTC (permalink / raw)
To: Alan Lawrence; +Cc: gcc-patches
On 23/04/14 16:20, Alan Lawrence wrote:
> This patch is a small tidy of a more-complicated expression that just flips a
> single bit and can thus be a simple XOR.
>
> No regressions on aarch64-none-elf or aarch64_be-none-elf. (I've verified code
> is indeed exercised by dg-torture.exp vshuf-v*.c).
>
> Also ok after applying TBL and testsuite patches in
> http://gcc.gnu.org/ml/gcc-patches/2014-04/msg01309.html and
> http://gcc.gnu.org/ml/gcc-patches/2014-04/msg00579.html.
>
> gcc/ChangeLog:
> 2014-04-23 Alan Lawrence <alan.lawrence@arm.com>
>
> * config/aarch64/aarch64.c (aarch64_expand_vec_perm_1): tidy bit-flip expression.
>
s/tidy/Tidy/
It's not obvious from your description (or from the code, for that
matter) that for this to be valid nelt must be a power of 2.
I suggest that, above the loop, you put
gcc_assert (nelt == (nelt & -nelt));
OK with those changes.
R.
>
> xor_tidy.patch
>
>
> diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
> index a3147ee..b879754 100644
> --- a/gcc/config/aarch64/aarch64.c
> +++ b/gcc/config/aarch64/aarch64.c
> @@ -8124,7 +8124,7 @@ aarch64_expand_vec_perm_const_1 (struct expand_vec_perm_d *d)
> rtx x;
>
> for (i = 0; i < nelt; ++i)
> - d->perm[i] = (d->perm[i] + nelt) & (2 * nelt - 1);
> + d->perm[i] ^= nelt; /* Keep the same index, but in the other vector. */
>
> x = d->op0;
> d->op0 = d->op1;
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH AARCH64] One-line tidy of bit-twiddle expression in aarch64.c
2014-04-29 12:48 ` Richard Earnshaw
@ 2014-04-29 18:56 ` Richard Henderson
2014-05-02 15:12 ` Alan Lawrence
0 siblings, 1 reply; 4+ messages in thread
From: Richard Henderson @ 2014-04-29 18:56 UTC (permalink / raw)
To: Richard Earnshaw, Alan Lawrence; +Cc: gcc-patches
On 04/29/2014 05:42 AM, Richard Earnshaw wrote:
> On 23/04/14 16:20, Alan Lawrence wrote:
>> This patch is a small tidy of a more-complicated expression that just flips a
>> single bit and can thus be a simple XOR.
>>
>> No regressions on aarch64-none-elf or aarch64_be-none-elf. (I've verified code
>> is indeed exercised by dg-torture.exp vshuf-v*.c).
>>
>> Also ok after applying TBL and testsuite patches in
>> http://gcc.gnu.org/ml/gcc-patches/2014-04/msg01309.html and
>> http://gcc.gnu.org/ml/gcc-patches/2014-04/msg00579.html.
>>
>> gcc/ChangeLog:
>> 2014-04-23 Alan Lawrence <alan.lawrence@arm.com>
>>
>> * config/aarch64/aarch64.c (aarch64_expand_vec_perm_1): tidy bit-flip expression.
>>
>
> s/tidy/Tidy/
>
> It's not obvious from your description (or from the code, for that
> matter) that for this to be valid nelt must be a power of 2.
>
> I suggest that, above the loop, you put
>
> gcc_assert (nelt == (nelt & -nelt));
>
> OK with those changes.
I think it's sort of obvious from context that we're working with a vector.
And it also seems obvious that we won't have a vector without a power-of-two
number of elements.
r~
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH AARCH64] One-line tidy of bit-twiddle expression in aarch64.c
2014-04-29 18:56 ` Richard Henderson
@ 2014-05-02 15:12 ` Alan Lawrence
0 siblings, 0 replies; 4+ messages in thread
From: Alan Lawrence @ 2014-05-02 15:12 UTC (permalink / raw)
To: Richard Henderson, Richard Earnshaw; +Cc: gcc-patches
Whilst I agree with Richard H that it is obvious, my feeling is that the
assertion does no harm, so have committed rev 210005 with Richard E's changes.
--Alan
Richard Henderson wrote:
> On 04/29/2014 05:42 AM, Richard Earnshaw wrote:
>> On 23/04/14 16:20, Alan Lawrence wrote:
>>> This patch is a small tidy of a more-complicated expression that just flips a
>>> single bit and can thus be a simple XOR.
>>>
>>> No regressions on aarch64-none-elf or aarch64_be-none-elf. (I've verified code
>>> is indeed exercised by dg-torture.exp vshuf-v*.c).
>>>
>>> Also ok after applying TBL and testsuite patches in
>>> http://gcc.gnu.org/ml/gcc-patches/2014-04/msg01309.html and
>>> http://gcc.gnu.org/ml/gcc-patches/2014-04/msg00579.html.
>>>
>>> gcc/ChangeLog:
>>> 2014-04-23 Alan Lawrence <alan.lawrence@arm.com>
>>>
>>> * config/aarch64/aarch64.c (aarch64_expand_vec_perm_1): tidy bit-flip expression.
>>>
>> s/tidy/Tidy/
>>
>> It's not obvious from your description (or from the code, for that
>> matter) that for this to be valid nelt must be a power of 2.
>>
>> I suggest that, above the loop, you put
>>
>> gcc_assert (nelt == (nelt & -nelt));
>>
>> OK with those changes.
>
> I think it's sort of obvious from context that we're working with a vector.
> And it also seems obvious that we won't have a vector without a power-of-two
> number of elements.
>
>
> r~
>
>
^ permalink raw reply [flat|nested] 4+ messages in thread
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2014-04-23 15:29 [PATCH AARCH64] One-line tidy of bit-twiddle expression in aarch64.c Alan Lawrence
2014-04-29 12:48 ` Richard Earnshaw
2014-04-29 18:56 ` Richard Henderson
2014-05-02 15:12 ` Alan Lawrence
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