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From: "davidxl at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/46281] New: Inefficient unswitching (too many copies)
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46281

           Summary: Inefficient unswitching (too many copies)
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: davidxl@gcc.gnu.org


Compiling the following program with -O3:

extern int gen_int(int);
extern void ref_int_p(int*);

void kernel3 ()
{
  int i;
  int j;
  int k;
  int l;
  int m;
  int a[200];

  j = gen_int (0);
  k = gen_int (0);
  l = gen_int (0);
  m = gen_int (0);

  for (i = 0; i < 200; i++)
    {
      if (j < k || j < l || j < m ) // || j << 3 || k << 4)
        a[i] = 1;
      else
        a[i] -= j;
    }

  ref_int_p (&a[0]);

  return;
}


Gcc unswitches the loop, but generate three copies of the loop -- it should
only generate 2 copies.

LLVM correctly generates two copies.

David