[Bug tree-optimization/45215] New: Tree-optimization misses a trick with bit tests

[bernds at gcc dot gnu dot org]

The following testcase

int x (int t)
{
  if (t & 256)
    return -26;
  return 0;
}

can be implemented as a sequence of two shifts and one and operation:
        movl    4(%esp), %eax
        sall    $23, %eax
        sarl    $31, %eax
        andl    $-26, %eax
        ret

Initial RTL generation produces a more complicated sequence which is not
optimized unless the combiner is extended to handle four insns.  The tree
optimizers could be enhanced to handle this pattern and related ones, although
it would have to take costs into account, as on some targets other sequences
may be better.


-- 
           Summary: Tree-optimization misses a trick with bit tests
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bernds at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45215