Can anyone tell me why the following code:

  .sub _main
        .local PerlUndef val

        val = new PerlUndef
        _foo("bar", val)

        end
  .end

  .sub _foo
        .param string v1
        .param pmc v2

        .pcc_begin_return
        .return 1
        .pcc_end_return
  .end

Would produce the following output:

  cog:~/parrot test.imc
  wrong param count
          in file '(unknown file)' near line -1

It stems mainly from 2a below.

I recommend: (1) Using non_prototyped subs and explicit .pcc_call directives,
rather than the shorthand version for now.

Until I get some fixes committed you have a couple of other options:

(2) Don't mix PMCs and native types in argument lists if you use prototyped
subs
(2a) If you use PMCs, then IMCC won't coerce a constant argument into a
PMC yet. _foo("bar", val) will pass "bar" as a plain string type, even if
the prototype
expects a PMC. This is a bug.

I expect to have a large revision soon that will address lots of issues in
IMCC, but
it will most likely be in a new branch (imcc2) so as not to cause complete
chaos with
the "semi-stable" version. Then I will try to backpatch some of those fixes
into the
current IMCC.