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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/102224] [9/10/11/12 regession] wrong code for `x *
 copysign(1.0, x)` since r9-5298-g33142cf9cf82aa1f
Date: Tue, 07 Sep 2021 11:25:39 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102224

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |jakub at gcc dot gn=
u.org
             Status|NEW                         |ASSIGNED

--- Comment #11 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 51422
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D51422&action=3Dedit
gcc12-pr102224.patch

Untested fix.  It is actually a mess.
While we can during expansion emit efficient fabs code if the two input
operands are equal, we still need to ensure correctness for the case where =
the
operand equality is discovered only after expansion.
This patch does that by ensuring through early-clobber and constraints that
for pre-AVX dest=3D=3Dop1 is different from op0, because we want to overwri=
te op1
first with op1 & mask before using op0.  For AVX, the constraints ensure th=
at
either all of dest, op0 and op1 are different, or any two of them are the s=
ame
but the third one is different.  If op0 and op1 are different, then it is ok
without further changes, the i386-expand.c changes are for the op0 =3D=3D o=
p1 case
where we've ensured that dest is different from the inputs - we can emit vp=
andn
but if the mask is in memory, we need to force it into a register and can u=
se
dest for that.=