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From: "652023330028 at smail dot nju.edu.cn" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/114511] New: [Regression] Missed
 optimization: x = -y; x = c + x + y; ==> x=c;
Date: Thu, 28 Mar 2024 07:24:25 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 14.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114511

            Bug ID: 114511
           Summary: [Regression] Missed optimization: x =3D -y; x =3D c + x=
 +
                    y; =3D=3D> x=3Dc;
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: 652023330028 at smail dot nju.edu.cn
  Target Milestone: ---

Hello, we noticed that y can be eliminated from the calculation of x in the
following code. (x =3D c)

https://godbolt.org/z/716814Eh5

int x, y;
void func(int a, int b, int c, int d){
    y =3D d / a + (-b + a);
    x =3D -y;
    x =3D c + x + y;
}

But GCC -O3 -fwrapv:
  <bb 2> [local count: 1073741824]:
  # DEBUG BEGIN_STMT
  _1 =3D d_7(D) / a_8(D);
  _2 =3D a_8(D) - b_9(D);
  _3 =3D _1 + _2;
  y =3D _3;
  # DEBUG BEGIN_STMT
  _18 =3D b_9(D) + c_12(D);
  _19 =3D _18 - a_8(D);
  # DEBUG BEGIN_STMT
  _20 =3D _3 + _19;
  _6 =3D _20 - _1;
  x =3D _6;
  return;

Expected code:
GCC-7.5 -O3 -fwrapv
  <bb 2> [100.00%]:
  _1 =3D d_7(D) / a_8(D);
  _2 =3D a_8(D) - b_9(D);
  _3 =3D _1 + _2;
  y =3D _3;
  x =3D c_12(D);
  return;

Thank you very much for your time and effort! We look forward to hearing fr=
om
you.=