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From: "ibuclaw at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/102673] New: [9 Regression] Wrong code with
 -O due to adjust_cond_for_loop_until_wrap
Date: Sat, 09 Oct 2021 21:38:48 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102673

            Bug ID: 102673
           Summary: [9 Regression] Wrong code with -O due to
                    adjust_cond_for_loop_until_wrap
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ibuclaw at gcc dot gnu.org
  Target Milestone: ---

Reduced test, when compiled with -O, optimizes the loop into `return 1;`.
---
int main()
{
    for (unsigned a =3D 0, b =3D 0; a < 6; a +=3D 1, b +=3D 2)
    {
         if (b < a)
             return 1;
    }
    return 0;
}
---
https://godbolt.org/z/YM7aYrY8v

Bisected, and the commit that changed behaviour was the fix for pr84648.=