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

[Tamar Christina <Tamar.Christina@arm.com>]

> >     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