Re: [PATCH 2/2]AArch64 Add support for neg on v1df

[Richard Sandiford <richard.sandiford@arm.com>]

Tamar Christina <Tamar.Christina@arm.com> writes:
>> -----Original Message-----
>> From: Richard Sandiford <richard.sandiford@arm.com>
>> Sent: Friday, September 23, 2022 5:30 AM
>> To: Tamar Christina <Tamar.Christina@arm.com>
>> Cc: gcc-patches@gcc.gnu.org; nd <nd@arm.com>; Richard Earnshaw
>> <Richard.Earnshaw@arm.com>; Marcus Shawcroft
>> <Marcus.Shawcroft@arm.com>; Kyrylo Tkachov <Kyrylo.Tkachov@arm.com>
>> Subject: Re: [PATCH 2/2]AArch64 Add support for neg on v1df
>> 
>> Tamar Christina <tamar.christina@arm.com> writes:
>> > Hi All,
>> >
>> > This adds support for using scalar fneg on the V1DF type.
>> >
>> > Bootstrapped Regtested on aarch64-none-linux-gnu and no issues.
>> >
>> > Ok for master?
>> 
>> Why just this one operation though?  Couldn't we extend iterators like
>> GPF_F16 to include V1DF, avoiding the need for new patterns?
>> 
>
> Simply because it's the only one I know how to generate code for.
> I can change GPF_F16 but I don't know under which circumstances we'd generate
> a V1DF for the other operations.

We'd do it for things like:

__Float64x1_t foo (__Float64x1_t x) { return -x; }

if the pattern is available, instead of using subregs.  So one way
would be to scan the expand rtl dump for subregs.

If the point is that there is no observable difference between
defining 1-element vector ops and not, except for this one case,
then that suggests we should handle this case in target-independent
code instead.  There's no point forcing every target that has V1DF
to define a duplicate of the DF neg pattern.

Thanks,
Richard
>
> So if it's ok to do so without full test coverage I'm happy to do so...
>
> Tamar.
>
>> Richard
>> 
>> >
>> > Thanks,
>> > Tamar
>> >
>> > gcc/ChangeLog:
>> >
>> > 	* config/aarch64/aarch64-simd.md (negv1df2): New.
>> >
>> > gcc/testsuite/ChangeLog:
>> >
>> > 	* gcc.target/aarch64/simd/addsub_2.c: New test.
>> >
>> > --- inline copy of patch --
>> > diff --git a/gcc/config/aarch64/aarch64-simd.md
>> > b/gcc/config/aarch64/aarch64-simd.md
>> > index
>> >
>> f4152160084d6b6f34bd69f0ba6386c1ab50f77e..cf8c094bd4b76981cef2dd5dd7
>> b8
>> > e6be0d56101f 100644
>> > --- a/gcc/config/aarch64/aarch64-simd.md
>> > +++ b/gcc/config/aarch64/aarch64-simd.md
>> > @@ -2713,6 +2713,14 @@ (define_insn "neg<mode>2"
>> >    [(set_attr "type" "neon_fp_neg_<stype><q>")]
>> >  )
>> >
>> > +(define_insn "negv1df2"
>> > + [(set (match_operand:V1DF 0 "register_operand" "=w")
>> > +       (neg:V1DF (match_operand:V1DF 1 "register_operand" "w")))]
>> > +"TARGET_SIMD"
>> > + "fneg\\t%d0, %d1"
>> > +  [(set_attr "type" "neon_fp_neg_d")]
>> > +)
>> > +
>> >  (define_insn "abs<mode>2"
>> >   [(set (match_operand:VHSDF 0 "register_operand" "=w")
>> >         (abs:VHSDF (match_operand:VHSDF 1 "register_operand" "w")))]
>> > diff --git a/gcc/testsuite/gcc.target/aarch64/simd/addsub_2.c
>> > b/gcc/testsuite/gcc.target/aarch64/simd/addsub_2.c
>> > new file mode 100644
>> > index
>> >
>> 0000000000000000000000000000000000000000..55a7365e897f8af509de953129
>> e0
>> > f516974f7ca8
>> > --- /dev/null
>> > +++ b/gcc/testsuite/gcc.target/aarch64/simd/addsub_2.c
>> > @@ -0,0 +1,22 @@
>> > +/* { dg-do compile } */
>> > +/* { dg-options "-Ofast" } */
>> > +/* { dg-final { check-function-bodies "**" "" "" { target { le } } }
>> > +} */
>> > +
>> > +#pragma GCC target "+nosve"
>> > +
>> > +/*
>> > +** f1:
>> > +** ...
>> > +**	fneg	d[0-9]+, d[0-9]+
>> > +**	fadd	v[0-9]+.2s, v[0-9]+.2s, v[0-9]+.2s
>> > +** ...
>> > +*/
>> > +void f1 (float *restrict a, float *restrict b, float *res, int n) {
>> > +   for (int i = 0; i < 2; i+=2)
>> > +    {
>> > +      res[i+0] = a[i+0] + b[i+0];
>> > +      res[i+1] = a[i+1] - b[i+1];
>> > +    }
>> > +}
>> > +