[Bug java/15525] New: suggestion to enable cast elimination

tromey at gcc dot gnu dot org gcc-bugzilla@gcc.gnu.org
Tue May 18 20:42:00 GMT 2004


Diego pointed out on irc today that we could eliminate some
casts by changing the java gimplifier a bit to allow CCP to
do the work for us.

Eg, consider this idiom:

    if (! (x instanceof foo))
      return false;
    foo self = (foo) x;

We could generate code like so:

    int tmp_1 = 0;
    if (! (_Jv_IsInstanceOf (x, &foo.class)) return 0;
    else tmp_1 = 1;

    foo self = tmp_1 ? (foo) x : _Jv_CheckCast (x, &foo.class);

We could do this when generating code for "instanceof" along these lines:
    _Jv_IsInstanceOf(...) ? ({ tmp_1 = 1; 1 }) : 0

With this approach, redundant calls to _Jv_CheckCast would be
automatically eliminated.  Perhaps then we could have an extra
pass to get rid of any remaining temporary variables that we introduced.

-- 
           Summary: suggestion to enable cast elimination
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P2
         Component: java
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: tromey at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org,java-prs at gcc dot gnu
                    dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15525



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