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


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~





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