fix opt/8634

[Zdenek Dvorak]

Hello,

> > > Zdenek Dvorak <rakdver@atrey.karlin.mff.cuni.cz> writes:
> > > 
> > > > Hello,
> > > > 
> > > > >     I believe purge_addressof costs us almost nothing
> > > > > 
> > > > > Not at all true, since it can iterate over all insns, so if you have a
> > > > > mechanism that calls it a fixed percentage of the time, it's actually
> > > > > *quadratic*.
> > > > 
> > > > can you explain this in greater detail? It is one pass over insns, so it
> > > > should be linear, no?
> > > 
> > > If you take a linear operation (that is, O(n)), and then you perform
> > > it K*n times for some fixed constant K, then the program is O(n*n),
> > > which is quadratic.
> > 
> > Why do you think purge_adressof does linear work per insn?
> 
> I don't.  I don't think anyone does.  Richard was saying that if
> purge_addressof is linear in the number of insns, and you then call it
> a number of times that's proportional to the number of insns, that
> makes it quadratic.

but as it is called exacly once per each function, it is linear.

Zdenek