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

[James Greenhalgh <james.greenhalgh@arm.com>]

On Wed, Jun 07, 2017 at 12:38:37PM +0100, Tamar Christina wrote:
> Hi All, 
> 
> 
> This patch adds support for creating floating point constants
> using mov immediate instructions.  The movi SIMD instruction can
> be used for HFmode and SFmode constants, eg. for -0.0f we generate:
> 
>         movi     v0.2s, 0x80, lsl 24
> 
> More complex constants can be generated using an integer MOV or
> MOV+MOVK:
> 
>      mov   w0, 48128
>      movk  w0, 0x47f0, lsl 16
>      fmov  s0, w0
> 
> We allow up to 3 instructions as this allows all HF, SF and most DF
> constants to be generated without a literal load, and is overall best
> for codesize.
> 
> 
> Regression tested on aarch64-none-linux-gnu and no regressions.
> 
> OK for trunk?
> 
> diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md
> index 5adc5edb8dde9c30450b04932a37c41f84cc5ed1..7f107672882b13809be01355ffafbc2807cc5adb 100644
> --- a/gcc/config/aarch64/aarch64.md
> +++ b/gcc/config/aarch64/aarch64.md
> @@ -1167,66 +1167,120 @@
>    }
>  )
>  
> -(define_insn "*movhf_aarch64"
> -  [(set (match_operand:HF 0 "nonimmediate_operand" "=w,w  ,?r,w,w,m,r,m ,r")
> -	(match_operand:HF 1 "general_operand"      "Y ,?rY, w,w,m,w,m,rY,r"))]
> +(define_insn_and_split "*movhf_aarch64"
> +  [(set (match_operand:HF 0 "nonimmediate_operand" "=w,w  ,?r,w,w  ,w  ,w,m,r,m ,r")
> +	(match_operand:HF 1 "general_operand"      "Y ,?rY, w,w,Ufc,Uvi,m,w,m,rY,r"))]
>    "TARGET_FLOAT && (register_operand (operands[0], HFmode)
> -    || aarch64_reg_or_fp_zero (operands[1], HFmode))"
> +    || aarch64_reg_or_fp_float (operands[1], HFmode))"
>    "@
>     movi\\t%0.4h, #0
> -   mov\\t%0.h[0], %w1
> +   fmov\\t%s0, %w1

Should this not be %h0?

>     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