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Re: [PATCH 1/2, x86] Add palignr support for AVX2.


On Wed, Oct 01, 2014 at 12:28:51PM +0200, Uros Bizjak wrote:
> On Wed, Oct 1, 2014 at 12:16 PM, Evgeny Stupachenko <evstupac@gmail.com> wrote:
> > Getting back to initial patch, is it ok?
> 
> IMO, we should start with Jakub's proposed patch [1]
> 
> [1] https://gcc.gnu.org/ml/gcc-patches/2014-10/msg00010.html

That doesn't compile, will post a new version; got interrupted when
I found that in
GCC_TEST_RUN_EXPENSIVE=1 make check-gcc RUNTESTFLAGS='--target_board=unix/-mavx2 dg-torture.exp=vshuf*.c'
one test is miscompiled even with unpatched compiler, debugging that now.

That said, my patch will not do anything about the
case Mark mentioned { 1, 2, 3, ..., 31, 0 } permutation,
for that we can't do vpalignr followed by vpshufb or similar,
but need to do some permutation first and then vpalignr on
the result.  So it would need a new routine.  It is still a 2
insn permutation, not 6, and needs different algorithm, so sharing
the same routine for that is undesirable.

	Jakub


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