Bootstrap failure of gcc-ss-20010409 in ia64

[Joe Buck]

> > > The debugger can't really be expected to print out information
> > > about the values of variables that were optimized away, for
> > > example.
> > This is the only case that is "unattainable".

Mike Stump writes:
> Actually, if you can make it spit out 5, when a user says p i, when
> the software has a { const int i = 5; } then I don't see why you can't
> mostly solve the last as well.  In fact, I thought dwarf 2 had enough
> guts to do this.

I suppose we could give the debugger a formula for re-generating things
like loop induction variables that get optimized away.  Kind of like a
spreadsheet, defining no longer existing variables in terms of existing
objects, perhaps different for each location.

But there also can be variables that are neither used nor set, so their
value is indeterminate.  Or because a variable is not used, the compiler
throws away a lot of code that computes it, and it might be tricky to
include all needed formulas to compute it.