On Tue, Nov 14, 2023 at 11:04 AM Xi Ruoyao <xry...@xry111.site> wrote:
>
> From: Andrew Pinski <pins...@gmail.com>
>
> On targets with native copysign instructions, (copysign x, -1) is
> usually more efficient than (fneg (fabs x)). Since r14-5284, in the
> middle end we always optimize (fneg (fabs x)) to (copysign x, -1), not
> vice versa. If the target does not support native fcopysign,
> expand_COPYSIGN will expand it as (fneg (fabs x)) anyway.
>
> gcc/ChangeLog:
>
> PR rtl-optimization/112483
> * simplify-rtx.cc (simplify_binary_operation_1) <case COPYSIGN>:
> Call simplify_unary_operation for NEG instead of
> simplify_gen_unary.
> ---
>
> [xry111]:
>
> Following Andrew's suggestion, I bootstrapped and regtested this
> patch on loongarch64-linux-gnu. Now with
>
> float t(float x)
> {
> return __builtin_copysignf(x, -0.1234);
> }
>
> It correctly generates
>
> pcalau12i $r12,%pc_hi20(.LC0)
> fld.s $f1,$r12,%pc_lo12(.LC0)
> fcopysign.s $f0,$f0,$f1
> jr $r1
>
> instead of the de-optimized fabs.s and fneg.s
>
> Ok for trunk?
>
> gcc/simplify-rtx.cc | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/gcc/simplify-rtx.cc b/gcc/simplify-rtx.cc
> index 2d2e5a3c1ca..f3745d86aea 100644
> --- a/gcc/simplify-rtx.cc
> +++ b/gcc/simplify-rtx.cc
> @@ -4392,7 +4392,7 @@ simplify_ashift:
> real_convert (&f1, mode, CONST_DOUBLE_REAL_VALUE (trueop1));
> rtx tmp = simplify_gen_unary (ABS, mode, op0, mode);
> if (REAL_VALUE_NEGATIVE (f1))
> - tmp = simplify_gen_unary (NEG, mode, tmp, mode);
> + tmp = simplify_unary_operation (NEG, mode, tmp, mode);
shouldn't that be when either the ABS or the NEG simplify? And I wonder
when that happens - I suppose when op0 is CONST_DOUBLE only?
> return tmp;
> }
> if (GET_CODE (op0) == NEG || GET_CODE (op0) == ABS)
> --
> 2.42.1
>
