[Bug tree-optimization/102673] New: [9 Regression] Wrong code with -O due to adjust_cond_for_loop_until_wrap

[ibuclaw at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102673

            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 = 0, b = 0; a < 6; a += 1, b += 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.