tree ssa and type issues

[Thomas R. Truscott]

> | >   dfs = (bitmap *) xmalloc (last_basic_block * sizeof (bitmap *));
> | >                                                        ^^^^^^^^

It would be nice if gcc gave a warning for suspicious cases like this.
I did a crude warning for this, and ironically it found a bug in valgrind:

http://websvn.kde.org/trunk/valgrind/coregrind/vg_signals.c?rev=396554&r1=396296&r2=396554

A generally usable warning would need to weed out false positives
by warning only when the types are suspiciously mismatched (as were these.)

Tom Truscott