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

[Prathamesh Kulkarni <prathamesh.kulkarni@linaro.org>]

On Mon, 14 Jun 2021 at 16:15, Kyrylo Tkachov <Kyrylo.Tkachov@arm.com> wrote:
>
>
>
> > -----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)?
I think it follows the following rule for canonicalization from
tree_swap_operands_p:
  /* It is preferable to swap two SSA_NAME to ensure a canonical form
     for commutative and comparison operators.  Ensuring a canonical
     form allows the optimizers to find additional redundancies without
     having to explicitly check for both orderings.  */
  if (TREE_CODE (arg0) == SSA_NAME
      && TREE_CODE (arg1) == SSA_NAME
      && SSA_NAME_VERSION (arg0) > SSA_NAME_VERSION (arg1))
    return 1;

For the above test-case, it's ccp1 that inverts the comparison.
The input to ccp1 pass is:
  _12 = __builtin_neon_vabsv2sf (a_6(D));
  _14 = _12;
  _1 = _14;
  _11 = __builtin_neon_vabsv2sf (b_8(D));
  _16 = _11;
  _2 = _16;
  _3 = _1 >= _2;
  _4 = VEC_COND_EXPR <_3, { -1, -1 }, { 0, 0 }>;
  _10 = VIEW_CONVERT_EXPR<uint32x2_t>(_4);
  return _10;

_3 = _1 >= _2 is folded into:
_3 = _12 >= _11

Since _12 is higher ssa version than _11, it is canonicalized to:
_3 = _11 <= _12.

Thanks,
Prathamesh
> If so, ok.
> Thanks,
> Kyrill
>
>
> >
> > Thanks,
> > Prathamesh
> > >
> > > Thanks,
> > > Prathamesh
> > > >
> > > > Thanks,
> > > > Prathamesh