[Bug tree-optimization/67998] New: redundant test for 0 when also checking inequality

[Bug tree-optimization/67998] New: redundant test for 0 when also checking inequality

[rv at rasmusvillemoes dot dk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67998

            Bug ID: 67998
           Summary: redundant test for 0 when also checking inequality
           Product: gcc
           Version: 5.1.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rv at rasmusvillemoes dot dk
  Target Milestone: ---

int f(unsigned a, unsigned b)
{
        if (!a || b >= a)
                return 5;
        return 2;
}

compiles to

f(unsigned int, unsigned int):
        testl   %edi, %edi
        je      .L3
        cmpl    %esi, %edi
        jbe     .L3
        movl    $2, %eax
        ret
.L3:
        movl    $5, %eax
        ret

The first test is redundant, since if a is zero, the inequality is guaranteed
to hold.

[Bug tree-optimization/67998] redundant test for 0 when also checking inequality

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67998

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED
   Target Milestone|---                         |12.0
      Known to fail|                            |7.1.0

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Fixed already on the trunk, I have not tried any other version (except GCC 7
where it was still broken):
  <bb 2> [local count: 1073741824]:
  if (a_2(D) <= b_3(D))
    goto <bb 3>; [34.00%]
  else
    goto <bb 4>; [66.00%]

  <bb 3> [local count: 365072224]:

  <bb 4> [local count: 1073741824]:
  # _1 = PHI <5(3), 2(2)>