Re: May delete_trivially_dead_insns delete trapping insns?

[Michael Matz <matz at suse dot de>]

Hi,

On Fri, 22 Nov 2002, Jan Hubicka wrote:

> It uses delete_insn_and_edges to remove the insns.

Hmm, right, I overlooked that.

> > Why for Java, but not for other languages?  If there are no trapping insns
>
> Because Java requires all exceptions to happen.  So you can't remove
> dead insns that possibly trap.

Ok, then a patch is needed to prohibit that.  Will do that when I'm in
prague ;-)

> Can you take a look why delete_insn_and_edges didn't removed the
> edge?

It is possible that I confused it with some other place deleting the insn
(I had a local patch prohibiting deleting trapping insns, got an error,
removed the patch, got a different error, and before patching any further
I wanted to clarify the semantics on the list ;) ).  For instance
reg-stack.c also uses bare delete_insn() (without checking trapping btw.)
but in the end calls fixup_abnormal_edges().  The latter becomes mightyly
confused if it finds exception edges but no trapping insns.

I wonder if for sanity-checking we should include a abort() in
delete_insn(), which triggers, if
  (flag_non_call_exceptions && may_trap_p())
I bet it will trigger quite often for Java programs.  OTOH I'm not sure
enough about Java semantics to know if the above really is disallowed.


Ciao,
Michael.