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[Bug tree-optimization/15758] New: Convert "if (a >= b) X else if (a >= b) Y" into "if (a >= b) X else Y"


void bar1 (void);
void bar2 (void);

void
foo (unsigned int a, unsigned int b)
{
  if (a >= b)
    bar1 ();
  else if (a <= b)
    bar2 ();
}

The last tree-ssa form looks like so:

foo (a, b)
{
<bb 0>:
  if (a_1 >= b_2) goto <L0>; else goto <L1>;

<L0>:;
  bar1 () [tail call];
  goto <bb 4> (<L3>);

<L1>:;
  if (a_1 <= b_2) goto <L2>; else goto <L3>;

<L2>:;
  bar2 () [tail call];

<L3>:;
  return;

}

Note that we could simply say

foo (a, b)
{
<bb 0>:
  if (a_1 >= b_2) goto <L0>; else goto <L2>;

<L0>:;
  bar1 () [tail call];
  goto <bb 4> (<L3>);

<L2>:;
  bar2 () [tail call];

<L3>:;
  return;

}

because the second "if" is just the opposite of the first "if".
Note that the equality in the second "if" never holds.

-- 
           Summary: Convert "if (a >= b) X else if (a >= b) Y" into "if (a
                    >= b) X else Y"
           Product: gcc
           Version: 3.5.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kazu at cs dot umass dot edu
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15758


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