diff mbox series

Only allow (copysign x, NEG_CONST) -> (fneg (fabs x)) simplification for constant folding [PR112483]

Message ID 20231114100320.47373-1-xry111@xry111.site
State Unresolved
Headers
Series Only allow (copysign x, NEG_CONST) -> (fneg (fabs x)) simplification for constant folding [PR112483] |

Checks

Context Check Description
snail/gcc-patch-check warning Git am fail log

Commit Message

Xi Ruoyao Nov. 14, 2023, 9:59 a.m. UTC 
  From: Andrew Pinski <pinskia@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(-)

Comments

Xi Ruoyao Nov. 14, 2023, 9:14 p.m. UTC | #1 
On Tue, 2023-11-14 at 11:44 +0100, Richard Biener wrote:
> > 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);
> >           return tmp;
> >         }
> 
> shouldn't that be when either the ABS or the NEG simplify?

Simplify (copysign x, POSTIVE_CONST) to (abs x) is an optimization.  So
for a positive f1, tmp will just be (abs x) and we return it.

> And I wonder when that happens - I suppose when op0 is CONST_DOUBLE only?

Yes, it's Andrew's intention.
diff mbox series

Patch

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);
 	  return tmp;
 	}
       if (GET_CODE (op0) == NEG || GET_CODE (op0) == ABS)