A strange gcc behavior, and an argument against -Wno-unused

[Michael Snyder <msnyder at vmware dot com>]

Hey all,

We have "-Wno-unused" in our Makefile.in, as a result of which
we have accumulated a huge pool of unused variables, which
probably get optimized away and so don't hurt anything, but
which clutter up the code.

I was playing around with the idea of cleaning them up, and
so I removed the "-Wno-unused" from the makefile.

But the first thing that happened was that my compile failed
with the following warning (which of course was treated as an
error, because we also have -Werror):

    i386-tdep.c:4149: warning: statement with no effect

Now here's the line in question, from i386_process_record:

          ir.rm != ir.rex_b;

From context and other examples, I'm pretty sure that this
is a typo, and was meant to read "|=", not "!=".  No sweat,
I'll fix it, or submit it for review anyway.

BUT!  The fact that this escaped being detected by the compiler
bothers me a lot!  I don't know whether to think of it as a
compiler bug, or to reason "well, we said "don't warn us about
things that are unused, and this is basically an unused
statement".

So, for discussion, should we remove -Wno-unused?

Michael