> -----Original Message----- > From: Richard Biener <richard.guent...@gmail.com> > Sent: Monday, November 13, 2023 6:55 AM > To: Xi Ruoyao <xry...@xry111.site> > Cc: gcc-patches@gcc.gnu.org; chenglulu <chengl...@loongson.cn>; > i...@xen0n.name; xucheng...@loongson.cn; Tamar Christina > <tamar.christ...@arm.com>; tschwi...@gcc.gnu.org; Roger Sayle > <ro...@nextmovesoftware.com> > Subject: Re: [PATCH] Fix (fcopysign x, NEGATIVE_CONST) -> (fneg (fabs x)) > simplification [PR112483] > > On Sun, Nov 12, 2023 at 9:27 PM Xi Ruoyao <xry...@xry111.site> wrote: > > > > (fcopysign x, NEGATIVE_CONST) can be simplified to (fneg (fabs x)), > > but a logic error in the code caused it mistakenly simplified to (fneg > > x) instead.
The fix aside, I actually wonder if simplify-rtx.cc should be doing this at all. The mid-end didn't do it because the target said it had an optab for the copysign operation. Otherwise during expand_COPYSIGN it would have been expanded as FNEG (FABS (..)) already. In the case of e.g. longaarch64 It looks like the target actually has an fcopysign Instruction, so wouldn't this rewriting by simplify-rtx be a de-optimization? Thanks, Tamar > > OK. > > > gcc/ChangeLog: > > > > PR rtl-optimization/112483 > > * simplify-rtx.cc (simplify_binary_operation_1) <case COPYSIGN>: > > Fix the simplification of (fcopysign x, NEGATIVE_CONST). > > --- > > > > Bootstrapped and regtested on loongarch64-linux-gnu and > > x86_64-linux-gnu. 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 > > 69d87579d9c..2d2e5a3c1ca 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, op0, mode); > > + tmp = simplify_gen_unary (NEG, mode, tmp, mode); > > return tmp; > > } > > if (GET_CODE (op0) == NEG || GET_CODE (op0) == ABS) > > -- > > 2.42.1 > >
