[Bug optimization/15350] New: [tree-ssa] Convert if ((1 << a) & 1) into if (a == 0).

[kazu at cs dot umass dot edu]

Convert foo() into baz().

void bar (void);

void
foo (int a)
{
  int b = 1 << a;
  if (b & 1)
    bar ();
}

void
baz (int a)
{
  if (a == 0)
    bar ();
}

You might think this is so artificial but actually comes from
simplify_comparison() in combine.c, a part of which looks like

<L344>:;
  T.4338_976 = (int)T.4337_966;
  T.4546_977 = T.4338_976 - 1;
  T.4547_978 = 1 << T.4546_977;
  T.4548_979 = T.4547_978 & 1;
  T.4549_980 = (_Bool)T.4548_979;
  if (T.4549_980 == 0) goto <L555>; else goto <L345>;

-- 
           Summary: [tree-ssa] Convert if ((1 << a) & 1) into if (a == 0).
           Product: gcc
           Version: tree-ssa
            Status: UNCONFIRMED
          Keywords: pessimizes-code
          Severity: enhancement
          Priority: P2
         Component: 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=15350