Fix a tcb crash and a potential bug on mainline

[Jeffrey A Law]

On Tue, 2004-10-19 at 16:23, Daniel Berlin wrote:

> Only if your pass performs *all* insertions and updates to statements 
> before performing *any* removals of statements.
True.  However, I believe that is the case for most of our optimizers
right now.

> I believe some passes don't do this right now.
PRE and jump threading being the obvious exceptions.

> Otherwise, in the intermediate step, we would think some statements are 
> dead when they are only dead because we haven't fixed them up yet :)
Right -- which is one of my big concerns with integrated dead
code elimination schemes.  This kind of problem bit us with
delete_insn as well.

jeff