[PATCH][GCC][AArch64] optimize float immediate moves (2 /4) - HF/DF/SF mode.

[Tamar Christina]

Ping
________________________________________
From: gcc-patches-owner@gcc.gnu.org <gcc-patches-owner@gcc.gnu.org> on behalf of Tamar Christina <Tamar.Christina@arm.com>
Sent: Monday, June 26, 2017 11:50:51 AM
To: James Greenhalgh
Cc: GCC Patches; nd; Marcus Shawcroft; Richard Earnshaw
Subject: Re: [PATCH][GCC][AArch64] optimize float immediate moves (2 /4) - HF/DF/SF mode.

Hi all,

Here's the re-spun patch.
Aside from the grouping of the split patterns it now also uses h register for the fmov for HF when available,
otherwise it forces a literal load.

Regression tested on aarch64-none-linux-gnu and no regressions.

OK for trunk?

Thanks,
Tamar


gcc/
2017-06-26  Tamar Christina  <tamar.christina@arm.com>
            Richard Sandiford <richard.sandiford@linaro.org>

        * config/aarch64/aarch64.md (mov<mode>): Generalize.
        (*movhf_aarch64, *movsf_aarch64, *movdf_aarch64):
        Add integer and movi cases.
        (movi-split-hf-df-sf split, fp16): New.
        (enabled): Added TARGET_FP_F16INST.
        * config/aarch64/iterators.md (GPF_HF): New.
________________________________________
From: Tamar Christina
Sent: Wednesday, June 21, 2017 11:48:33 AM
To: James Greenhalgh
Cc: GCC Patches; nd; Marcus Shawcroft; Richard Earnshaw
Subject: RE: [PATCH][GCC][AArch64] optimize float immediate moves (2 /4) - HF/DF/SF mode.

> >     movi\\t%0.4h, #0
> > -   mov\\t%0.h[0], %w1
> > +   fmov\\t%s0, %w1
>
> Should this not be %h0?

The problem is that H registers are only available in ARMv8.2+,
I'm not sure what to do about ARMv8.1 given your other feedback
Pointing out that the bit patterns between how it's stored in s vs h registers
differ.

>
> >     umov\\t%w0, %1.h[0]
> >     mov\\t%0.h[0], %1.h[0]
> > +   fmov\\t%s0, %1
>
> Likewise, and much more important for correctness as it changes the way the
> bit pattern ends up in the register (see table C2-1 in release B.a of the ARM
> Architecture Reference Manual for ARMv8-A), here.
>
> > +   * return aarch64_output_scalar_simd_mov_immediate (operands[1],
> > + SImode);
> >     ldr\\t%h0, %1
> >     str\\t%h1, %0
> >     ldrh\\t%w0, %1
> >     strh\\t%w1, %0
> >     mov\\t%w0, %w1"
> > -  [(set_attr "type"
> "neon_move,neon_from_gp,neon_to_gp,neon_move,\
> > -                     f_loads,f_stores,load1,store1,mov_reg")
> > -   (set_attr "simd" "yes,yes,yes,yes,*,*,*,*,*")]
> > +  "&& can_create_pseudo_p ()
> > +   && !aarch64_can_const_movi_rtx_p (operands[1], HFmode)
> > +   && !aarch64_float_const_representable_p (operands[1])
> > +   &&  aarch64_float_const_rtx_p (operands[1])"
> > +  [(const_int 0)]
> > +  "{
> > +    unsigned HOST_WIDE_INT ival;
> > +    if (!aarch64_reinterpret_float_as_int (operands[1], &ival))
> > +      FAIL;
> > +
> > +    rtx tmp = gen_reg_rtx (SImode);
> > +    aarch64_expand_mov_immediate (tmp, GEN_INT (ival));
> > +    tmp = simplify_gen_subreg (HImode, tmp, SImode, 0);
> > +    emit_move_insn (operands[0], gen_lowpart (HFmode, tmp));
> > +    DONE;
> > +  }"
> > +  [(set_attr "type" "neon_move,f_mcr,neon_to_gp,neon_move,fconsts,
> \
> > +                neon_move,f_loads,f_stores,load1,store1,mov_reg")
> > +   (set_attr "simd" "yes,*,yes,yes,*,yes,*,*,*,*,*")]
> >  )
>
> Thanks,
> James