[Bug tree-optimization/31657] New: Should combine bit tests in if stmts

[rguenth at gcc dot gnu dot org]

1)

  if (X & (1 << a))
    if (X & (1 << b))

  should be combined to

  tmp = (1 << a) | (1 << b)
  if (X & tmp == tmp)

2)

  if (X & a)
    goto doit;
  else
    if (X & b)
      goto doit

 doit:

  (i.e. the CFG form of (X & a || X & b))

 should be combined to
  if (X & (a | b))
    goto doit


The first form happens in SPEC2k6 libquantum hottest loop.  The patch I
have for this should also be made to address PR15353.


-- 
           Summary: Should combine bit tests in if stmts
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
        AssignedTo: rguenth at gcc dot gnu dot org
        ReportedBy: rguenth at gcc dot gnu dot org
OtherBugsDependingO 15353,15357,26163
             nThis:


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31657