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From: "kristerw at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/106883] New: SLSR may generate signed wrap
Date: Thu, 08 Sep 2022 00:05:37 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 13.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106883

            Bug ID: 106883
           Summary: SLSR may generate signed wrap
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kristerw at gcc dot gnu.org
  Target Milestone: ---

SLSR may generate new signed wrap for cases where the original did not wrap.
This can be seen in the function f from gcc.dg/tree-ssa/slsr-19.c:

int
f (int c, int s)
{
  int x1, x2, y1, y2;

  y1 =3D c + 2;
  x1 =3D s * y1;
  y2 =3D y1 + 2;
  x2 =3D s * y2;
  return x1 + x2;
}

SLSR optimizes this to

int f (int c, int s)
{
   int y1;
   int x2;
   int x1;
   int _7;
   int slsr_9;

   <bb 2>:
   y1_2 =3D c_1(D) + 2;
   x1_4 =3D y1_2 * s_3(D);
   slsr_9 =3D s_3(D) * 2;
   x2_6 =3D x1_4 + slsr_9;
   _7 =3D x1_4 + x2_6;
   return _7;

Calling f(-3, 0x75181005) does not make any operation wrap in the original
function, but slsr_9 overflow in the optimized code.=