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From: "juzhe.zhong at rivai dot ai" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/113583] Main loop in 519.lbm not vectorized.
Date: Wed, 07 Feb 2024 08:13:39 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113583

--- Comment #16 from JuzheZhong <juzhe.zhong at rivai dot ai> ---
The FMA is generated in widening_mul PASS:

Before widening_mul (fab1):

  _5 =3D 3.33333333333333314829616256247390992939472198486328125e-1 - _4;
  _6 =3D _5 * 1.229999999999999982236431605997495353221893310546875e-1;
  _8 =3D _4 + _6;

After widening_mul:

  _5 =3D 3.33333333333333314829616256247390992939472198486328125e-1 - _4;
  _8 =3D .FMA (_5, 1.229999999999999982236431605997495353221893310546875e-1=
, _4);

I think it's obvious, widening_mul choose to transform later 2 STMTs:

  _6 =3D _5 * 1.229999999999999982236431605997495353221893310546875e-1;
  _8 =3D _4 + _6;

into:

 _8 =3D .FMA (_5, 1.229999999999999982236431605997495353221893310546875e-1,=
 _4);

without any re-association.=