LoongArch: Fix wrong LSX FP vector negation

We expanded (neg x) to (minus const0 x) for LSX FP vectors, this is
wrong because -0.0 is not 0 - 0.0.  This causes some Python tests to
fail when Python is built with LSX enabled.

Use the vbitrevi.{d/w} instructions to simply reverse the sign bit
instead.  We are already doing this for LASX and now we can unify them
into simd.md.

gcc/ChangeLog:

	* config/loongarch/lsx.md (neg<mode:FLSX>2): Remove the
	incorrect expand.
	* config/loongarch/simd.md (simdfmt_as_i): New define_mode_attr.
	(elmsgnbit): Likewise.
	(neg<mode:FVEC>2): New define_insn.
	* config/loongarch/lasx.md (negv4df2, negv8sf2): Remove as they
	are now instantiated in simd.md.
---

Bootstrapped and regtested on loongarch64-linux-gnu.  Ok for trunk?

 gcc/config/loongarch/lasx.md | 16 ----------------
 gcc/config/loongarch/lsx.md  | 11 -----------
 gcc/config/loongarch/simd.md | 18 ++++++++++++++++++
 3 files changed, 18 insertions(+), 27 deletions(-)

在 2024/2/3 下午4:58, Xi Ruoyao 写道:
> We expanded (neg x) to (minus const0 x) for LSX FP vectors, this is
> wrong because -0.0 is not 0 - 0.0.  This causes some Python tests to
> fail when Python is built with LSX enabled.
>
> Use the vbitrevi.{d/w} instructions to simply reverse the sign bit
> instead.  We are already doing this for LASX and now we can unify them
> into simd.md.
>
> gcc/ChangeLog:
>
> 	* config/loongarch/lsx.md (neg<mode:FLSX>2): Remove the
> 	incorrect expand.
> 	* config/loongarch/simd.md (simdfmt_as_i): New define_mode_attr.
> 	(elmsgnbit): Likewise.
> 	(neg<mode:FVEC>2): New define_insn.
> 	* config/loongarch/lasx.md (negv4df2, negv8sf2): Remove as they
> 	are now instantiated in simd.md.
> ---
>
> Bootstrapped and regtested on loongarch64-linux-gnu.  Ok for trunk?

LGTM!

Thanks!

>
>   gcc/config/loongarch/lasx.md | 16 ----------------
>   gcc/config/loongarch/lsx.md  | 11 -----------
>   gcc/config/loongarch/simd.md | 18 ++++++++++++++++++
>   3 files changed, 18 insertions(+), 27 deletions(-)
>
> diff --git a/gcc/config/loongarch/lasx.md b/gcc/config/loongarch/lasx.md
> index e2115ffb884..ac84db7f0ce 100644
> --- a/gcc/config/loongarch/lasx.md
> +++ b/gcc/config/loongarch/lasx.md
> @@ -3028,22 +3028,6 @@ (define_insn "absv8sf2"
>     [(set_attr "type" "simd_logic")
>      (set_attr "mode" "V8SF")])
>   
> -(define_insn "negv4df2"
> -  [(set (match_operand:V4DF 0 "register_operand" "=f")
> -	(neg:V4DF (match_operand:V4DF 1 "register_operand" "f")))]
> -  "ISA_HAS_LASX"
> -  "xvbitrevi.d\t%u0,%u1,63"
> -  [(set_attr "type" "simd_logic")
> -   (set_attr "mode" "V4DF")])
> -
> -(define_insn "negv8sf2"
> -  [(set (match_operand:V8SF 0 "register_operand" "=f")
> -	(neg:V8SF (match_operand:V8SF 1 "register_operand" "f")))]
> -  "ISA_HAS_LASX"
> -  "xvbitrevi.w\t%u0,%u1,31"
> -  [(set_attr "type" "simd_logic")
> -   (set_attr "mode" "V8SF")])
> -
>   (define_insn "xvfmadd<mode>4"
>     [(set (match_operand:FLASX 0 "register_operand" "=f")
>   	(fma:FLASX (match_operand:FLASX 1 "register_operand" "f")
> diff --git a/gcc/config/loongarch/lsx.md b/gcc/config/loongarch/lsx.md
> index 7002edae4d4..b9b94b9079c 100644
> --- a/gcc/config/loongarch/lsx.md
> +++ b/gcc/config/loongarch/lsx.md
> @@ -728,17 +728,6 @@ (define_expand "neg<mode>2"
>     DONE;
>   })
>   
> -(define_expand "neg<mode>2"
> -  [(set (match_operand:FLSX 0 "register_operand")
> -	(neg:FLSX (match_operand:FLSX 1 "register_operand")))]
> -  "ISA_HAS_LSX"
> -{
> -  rtx reg = gen_reg_rtx (<MODE>mode);
> -  emit_move_insn (reg, CONST0_RTX (<MODE>mode));
> -  emit_insn (gen_sub<mode>3 (operands[0], reg, operands[1]));
> -  DONE;
> -})
> -
>   (define_expand "lsx_vrepli<mode>"
>     [(match_operand:ILSX 0 "register_operand")
>      (match_operand 1 "const_imm10_operand")]
> diff --git a/gcc/config/loongarch/simd.md b/gcc/config/loongarch/simd.md
> index cb0a19447a1..00ff2823a4e 100644
> --- a/gcc/config/loongarch/simd.md
> +++ b/gcc/config/loongarch/simd.md
> @@ -85,12 +85,21 @@ (define_mode_attr simdfmt [(V2DF "d") (V4DF "d")
>   (define_mode_attr simdifmt_for_f [(V2DF "l") (V4DF "l")
>   				  (V4SF "w") (V8SF "w")])
>   
> +;; Suffix for integer mode in LSX or LASX instructions to operating FP
> +;; vectors using integer vector operations.
> +(define_mode_attr simdfmt_as_i [(V2DF "d") (V4DF "d")
> +				(V4SF "w") (V8SF "w")])
> +
>   ;; Size of vector elements in bits.
>   (define_mode_attr elmbits [(V2DI "64") (V4DI "64")
>   			   (V4SI "32") (V8SI "32")
>   			   (V8HI "16") (V16HI "16")
>   			   (V16QI "8") (V32QI "8")])
>   
> +;; The index of sign bit in FP vector elements.
> +(define_mode_attr elmsgnbit [(V2DF "63") (V4DF "63")
> +			     (V4SF "31") (V8SF "31")])
> +
>   ;; This attribute is used to form an immediate operand constraint using
>   ;; "const_<bitimm>_operand".
>   (define_mode_attr bitimm [(V16QI "uimm3") (V32QI "uimm3")
> @@ -457,6 +466,15 @@ (define_expand "reduc_<fmaxmin>_scal_<mode>"
>     DONE;
>   })
>   
> +;; FP negation.
> +(define_insn "neg<mode>2"
> +  [(set (match_operand:FVEC 0 "register_operand" "=f")
> +	(neg:FVEC (match_operand:FVEC 1 "register_operand" "f")))]
> +  ""
> +  "<x>vbitrevi.<simdfmt_as_i>\t%<wu>0,%<wu>1,<elmsgnbit>"
> +  [(set_attr "type" "simd_logic")
> +   (set_attr "mode" "<MODE>")])
> +
>   ; The LoongArch SX Instructions.
>   (include "lsx.md")
>

On Sun, 2024-02-04 at 11:20 +0800, chenglulu wrote:
> 
> 在 2024/2/3 下午4:58, Xi Ruoyao 写道:
> > We expanded (neg x) to (minus const0 x) for LSX FP vectors, this is
> > wrong because -0.0 is not 0 - 0.0.  This causes some Python tests to
> > fail when Python is built with LSX enabled.
> > 
> > Use the vbitrevi.{d/w} instructions to simply reverse the sign bit
> > instead.  We are already doing this for LASX and now we can unify them
> > into simd.md.
> > 
> > gcc/ChangeLog:
> > 
> > 	* config/loongarch/lsx.md (neg<mode:FLSX>2): Remove the
> > 	incorrect expand.
> > 	* config/loongarch/simd.md (simdfmt_as_i): New define_mode_attr.
> > 	(elmsgnbit): Likewise.
> > 	(neg<mode:FVEC>2): New define_insn.
> > 	* config/loongarch/lasx.md (negv4df2, negv8sf2): Remove as they
> > 	are now instantiated in simd.md.
> > ---
> > 
> > Bootstrapped and regtested on loongarch64-linux-gnu.  Ok for trunk?
> 
> LGTM!
> 
> Thanks!

Pushed r14-8785.