[PATCH][AArch64] Use 'x' constraint for vector HFmode multiplication by indexed element instructions

Kyrill Tkachov kyrylo.tkachov@foss.arm.com
Thu Mar 16 10:01:00 GMT 2017

Hi Christophe,

On 16/03/17 09:54, Christophe Lyon wrote:
> On 16 March 2017 at 10:29, Kyrill Tkachov <kyrylo.tkachov@foss.arm.com> wrote:
>> Hi all,
>> The advsimd-intrinsics.exp tests for the fmul and fmulx instructions that
>> perform a multiplication by indexed element
>> have started generating invalid assembly in my testing. For example:
>> Error: register number out of range 0 to 15 at operand 3 -- `fmulx
>> v24.8h,v23.8h,v22.h[0]'
> Are you configuring gcc in a special way? I can see no failure on trunk
> in advsimd-intrinsics tests at the moment.
> Should the tests be improved?

I was configuring with --with-cpu=cortex-a57.
I also have other patches in my tree that I've been experimenting with that modify AdvSIMD codegen
so maybe they triggered this. I haven't tried reproducing it with clean trunk (though I bootstrapped
and tested the patch applied on a clean trunk).
I think the tests did what they should and the assembler caught the error, so I don't see how the tests
could be improved in this case.


> Thanks,
> Christophe
>> The problem is that the indexed vector register (v22 in this case) has to be
>> in V0-V15 when accessed as a 16-bit element.
>> The constraints on the pattern don't reflect this. We already have the h_con
>> constraint that's supposed to do what we want,
>> but it incorrectly returns the "w" constraint for HF inner modes and it
>> isn't applied in all the patterns that it needs to be
>> (it's needed for the FMLA, FMLS, FMUL, FMULx by element patterns).
>> This patch fixes those issues by changing h_con to return the "x" constraint
>> for HF inner modes and applying it to all the operands
>> that need it in aarch64-simd.md
>> With this patch the advsimd-intrinsics.exp tests now generate valid assembly
>> and don't complain, so no new regression tests are added.
>> Bootstrapped and tested on aarch64-none-linux-gnu.
>> Ok for trunk?
>> Thanks,
>> Kyrill
>> 2017-03-16  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
>>      * config/aarch64/iterators.md (h_con): Return "x" for V4HF and V8HF.
>>      * config/aarch64/aarch64-simd.md (*aarch64_fma4_elt_from_dup<mode>):
>>      Use h_con constraint for operand 1.
>>      (*aarch64_fnma4_elt_from_dup<mode>): Likewise.
>>      (*aarch64_mulx_elt_from_dup<mode>): Likewise for operand 2.

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