On Fri, 5 Feb 2021 at 15:42, Kyrylo Tkachov <kyrylo.tkac...@arm.com> wrote:
>
> Hi Prathamesh,
>
> > -----Original Message-----
> > From: Prathamesh Kulkarni <prathamesh.kulka...@linaro.org>
> > Sent: 05 February 2021 09:53
> > To: gcc Patches <gcc-patches@gcc.gnu.org>; Kyrylo Tkachov
> > <kyrylo.tkac...@arm.com>
> > Subject: [PR97903][ARM] Missed optimization in lowering to vtst
> >
> > Hi,
> > For the following test-case:
> >
> > #include <arm_neon.h>
> >
> > uint8x8_t f1(int8x8_t a, int8x8_t b) {
> > return (uint8x8_t) ((a & b) != 0);
> > }
> >
> > gcc fails to lower test operation to vtst, and instead emits:
> > f1:
> > vand d0, d0, d1
> > vceq.i8 d0, d0, #0
> > vmvn d0, d0
> > bx lr
> >
> > The attached patch tries to fix this by adding a pattern to match this
> > combine:
> > Trying 7, 8 -> 9:
> > 7: r120:V8QI=r123:V8QI&r124:V8QI
> > REG_DEAD r124:V8QI
> > REG_DEAD r123:V8QI
> > 8: r122:V8QI=-r120:V8QI==const_vector
> > REG_DEAD r120:V8QI
> > 9: r121:V8QI=~r122:V8QI
> > REG_DEAD r122:V8QI
> > Failed to match this instruction:
> > (set (reg:V8QI 121)
> > (plus:V8QI (eq:V8QI (and:V8QI (reg:V8QI 123)
> > (reg:V8QI 124))
> > (const_vector:V8QI [
> > (const_int 0 [0]) repeated x8
> > ]))
> > (const_vector:V8QI [
> > (const_int -1 [0xffffffffffffffff]) repeated x8
> > ])))
> >
> > Essentially it converts:
> > r120 = (and r123 r124)
> > r122 = (neg (eq r120 0))
> > r121 = (not r122)
> > -->
> > r121 = vtst r123, r124
> >
> > (I guess it simplifies (not (neg X)) to (plus X -1) above).
> >
> > Code-gen after patch:
> > f1:
> > vtst.8 d0, d0, d1
> > bx lr
> >
>
> +(define_insn "neon_vtst_combine<mode>"
> + [(set (match_operand:VDQIW 0 "s_register_operand" "=w")
> + (plus:VDQIW
> + (eq:VDQIW
> + (and:VDQIW (match_operand:VDQIW 1 "s_register_operand" "w")
> + (match_operand:VDQIW 2 "s_register_operand" "w"))
> + (match_operand:VDQIW 3 "zero_operand" "i"))
> + (match_operand:VDQIW 4 "minus_one_operand" "i")))]
> + "TARGET_NEON"
> + "vtst.<V_sz_elem>\t%<V_reg>0, %<V_reg>1, %<V_reg>2"
> +)
>
> This will need a type attribute for scheduling.
>
> > Bootstrapped + tested on arm-linux-gnueabihf, and
> > cross tested on arm*-*-*.
> > Does it look OK for next stage-1 ?
>
> It looks sensible to me for stage 1.
Hi Kyrill,
Would it be OK to commit the attached patch after testing passes ?Thanks, Prathamesh > Thanks, > Kyrill > > > > > Thanks, > > Prathamesh
pr97903-2.diff
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