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From: "mital at mitalashok dot co.uk" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/114937] New: [11 regression] -ftree-vrp
 optimizes out range check before conditional increment
Date: Fri, 03 May 2024 13:41:31 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 11.4.0
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X-Bugzilla-Who: mital at mitalashok dot co.uk
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114937

            Bug ID: 114937
           Summary: [11 regression] -ftree-vrp optimizes out range check
                    before conditional increment
           Product: gcc
           Version: 11.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mital at mitalashok dot co.uk
  Target Milestone: ---

https://godbolt.org/z/fdMGWa4nq

    int f(int x) {
      const int y =3D x;
      if (x !=3D INT_MAX) {
        ++x;
      }

      return (x > y) ? x : 0;
    }

    int z =3D INT_MAX;
    int main(void) {
        // Prints INT_MIN when it should print 0
        __builtin_printf("%d\n", f(z));
    }

`f` is miscompiled at `-O1 -ftree-vrp` (also `-O2`) in GCC10/11 to return `=
x+1`
unconditionally.=20=20
The same happens with `if (x !=3D INT_MIN) --x; return (x < y) ? x : 0;`.

This does not happen in GCC9 or GCC12+=