[ARM] PR97906 - Missed lowering abs(a) >= abs(b) to vacge

Kyrylo Tkachov Kyrylo.Tkachov@arm.com
Mon Jun 14 10:45:36 GMT 2021



> -----Original Message-----
> From: Prathamesh Kulkarni <prathamesh.kulkarni@linaro.org>
> Sent: 14 June 2021 08:58
> To: gcc Patches <gcc-patches@gcc.gnu.org>; Kyrylo Tkachov
> <Kyrylo.Tkachov@arm.com>
> Subject: Re: [ARM] PR97906 - Missed lowering abs(a) >= abs(b) to vacge
> 
> On Mon, 7 Jun 2021 at 12:46, Prathamesh Kulkarni
> <prathamesh.kulkarni@linaro.org> wrote:
> >
> > On Tue, 1 Jun 2021 at 16:03, Prathamesh Kulkarni
> > <prathamesh.kulkarni@linaro.org> wrote:
> > >
> > > Hi,
> > > As mentioned in PR, for following test-case:
> > >
> > > #include <arm_neon.h>
> > >
> > > uint32x2_t f1(float32x2_t a, float32x2_t b)
> > > {
> > >   return vabs_f32 (a) >= vabs_f32 (b);
> > > }
> > >
> > > uint32x2_t f2(float32x2_t a, float32x2_t b)
> > > {
> > >   return (uint32x2_t) __builtin_neon_vcagev2sf (a, b);
> > > }
> > >
> > > We generate vacge for f2, but with -ffast-math, we generate following
> for f1:
> > > f1:
> > >         vabs.f32        d1, d1
> > >         vabs.f32        d0, d0
> > >         vcge.f32        d0, d0, d1
> > >         bx      lr
> > >
> > > This happens because, the middle-end inverts the comparison to b <= a,
> > > .optimized dump:
> > >  _8 = __builtin_neon_vabsv2sf (a_4(D));
> > >   _7 = __builtin_neon_vabsv2sf (b_5(D));
> > >   _1 = _7 <= _8;
> > >   _2 = VIEW_CONVERT_EXPR<vector(2) int>(_1);
> > >   _6 = VIEW_CONVERT_EXPR<uint32x2_t>(_2);
> > >   return _6;
> > >
> > > and combine fails to match the following pattern:
> > > (set (reg:V2SI 121)
> > >     (neg:V2SI (le:V2SI (abs:V2SF (reg:V2SF 123))
> > >             (abs:V2SF (reg:V2SF 122)))))
> > >
> > > because neon_vca<cmp_op><mode> pattern has GTGE code iterator.
> > > The attached patch adjusts the neon_vca patterns to use GLTE instead
> > > similar to neon_vca<cmp_op><mode>_fp16insn, and removes
> NEON_VACMP iterator.
> > > Code-gen with patch:
> > > f1:
> > >         vacle.f32       d0, d1, d0
> > >         bx      lr
> > >
> > > Bootstrapped + tested on arm-linux-gnueabihf and cross-tested on arm*-
> *-*.
> > > OK to commit ?

Is that inversion guaranteed to happen (is it a canonicalization rule)?
If so, ok.
Thanks,
Kyrill


> 
> Thanks,
> Prathamesh
> >
> > Thanks,
> > Prathamesh
> > >
> > > Thanks,
> > > Prathamesh


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