[PATCH AARCH64] One-line tidy of bit-twiddle expression in aarch64.c

[Alan Lawrence]

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~
> 
>