Re: [Patch, AArch64] Fix shuffle for big-endian.

[Alan Lawrence <alan dot lawrence at arm dot com>]

I've been doing some local testing using this patch as a basis for some of my
own work on NEON intrinsics, and it seems good to me. A couple of points:

(1) Re. the comment that "If two vectors, we end up with a wierd mixed-endian
mode on NEON": firstly "wierd" should be spelt "weird";
secondly, if I understand right, this comment belongs with the next "if
(!d->one_vector_p...)" rather than the "if (BYTES_BIG_ENDIAN)" before which it's
written.

(2) as you say, this code is not exercised, unless you do something to remove
the 'if (BYTES_BIG_ENDIAN) return false;' earlier in that same function. Can I
politely suggest you do that here in this patch?

(3) In my own regression testing, with const_vec_perm enabled on big_endian, I
see 2*PASS->FAIL, namely

gcc.dg/vect/vect-114.c scan-tree-dump-times vect "vectorized 0 loops" 1

gcc.dg/vect/vect-114.c -flto -ffat-lto-objects  scan-tree-dump-times
vect "vectorized 0 loops" 1

These are essentially noise, but the noise is removed and I see no other
problems, if (after this patch) I re-enable the testsuite's "vect_perm" target
selector for aarch64 big-endian (testsuite/lib/target-supports.exp). Would you
like a separate patch for that or roll it in here?

Cheers, Alan

Tejas Belagod wrote:
> > Hi,
> >
> > When a shuffle of more than one input happens, on NEON we end up with a
> > 'mixed-endian' format in the register list which TBL operates on. We don't 
make
> > this correction in RTL and therefore the shuffle operation gets it incorrect.
> > Here is a patch that fixes-up the index table in the selector rtx in RTL to 
also
> > be mixed-endian to reflect what's happening on NEON.
> >
> > As trunk stands, this patch will not be exercised as constant vector 
permute for
> > Big-endian is disabled. I've tested this by locally enabling const vec_perm 
and
> > it fixes the some regressions we have on big-endian:
> >
> > aarch64_be-none-elf:
> > FAIL->PASS: gcc.c-torture/execute/loop-11.c execution,  -O3 
-fomit-frame-pointer
> > FAIL->PASS: gcc.c-torture/execute/loop-11.c execution,  -O3 
-fomit-frame-pointer
> > -funroll-all-loops -finline-functions
> > FAIL->PASS: gcc.c-torture/execute/loop-11.c execution,  -O3 
-fomit-frame-pointer
> > -funroll-loops
> > FAIL->PASS: gcc.c-torture/execute/loop-11.c execution,  -O3 -g
> > FAIL->PASS: gcc.dg/torture/vector-shuffle1.c  -O0  execution test
> > FAIL->PASS: gcc.dg/torture/vshuf-v16qi.c  -O2  execution test
> > FAIL->PASS: gcc.dg/torture/vshuf-v2df.c  -O2  execution test
> > FAIL->PASS: gcc.dg/torture/vshuf-v2di.c  -O2  execution test
> > FAIL->PASS: gcc.dg/torture/vshuf-v2sf.c  -O2  execution test
> > FAIL->PASS: gcc.dg/torture/vshuf-v2si.c  -O2  execution test
> > FAIL->PASS: gcc.dg/torture/vshuf-v4sf.c  -O2  execution test
> > FAIL->PASS: gcc.dg/torture/vshuf-v4si.c  -O2  execution test
> > FAIL->PASS: gcc.dg/torture/vshuf-v8hi.c  -O2  execution test
> > FAIL->PASS: gcc.dg/torture/vshuf-v8qi.c  -O2  execution test
> > FAIL->PASS: gcc.dg/vect/vect-114.c -flto -ffat-lto-objects execution test
> > FAIL->PASS: gcc.dg/vect/vect-114.c execution test
> > FAIL->PASS: gcc.dg/vect/vect-15.c -flto -ffat-lto-objects execution test
> > FAIL->PASS: gcc.dg/vect/vect-15.c execution test
> >
> > Also regressed on aarch64-none-elf.
> >
> > OK for stage-1?
> >
> > Thanks,
> > Tejas.
> >
> > 2014-02-21  Tejas Belagod  <tejas.belagod@arm.com>
> >
> > gcc/
> > 	* config/aarch64/aarch64.c (aarch64_evpc_tbl): Fix index vector for
> > 	big-endian when dealing with more than one input shuffle vector.
> >