Re: Thoughts about semantics of BB_VISITED

[Daniel Berlin <dberlin at dberlin dot org>]

On Fri, 7 Jan 2005, Zdenek Dvorak wrote:

> Hello,
>
> > > because get_loop_body is often used on places where (lots of) new blocks
> > > get created (like unroller).  Resizing the sbitmap would be quite
> > > annoying.
> >
> > Also, it's quite annoying to have to keep resetting these flags.  I don't
> > think a simple read-only helper should be altering the basic block flags.
> > All i did was ask for the loop body.
>
> it does not change them -- they must be clear on the entry, and they are
> clear on the exit.

It will clear them if they aren't cleared, at least on some blocks.  This 
is obvious from the definition of dfs_enumerate_from.
Also, t requires you to change them before calling the routine, or the 
routine 
breaks.
This is the same as if the routine changed them itself, which it does (it 
clears them).

I'll note that other get_loop_* routines, like get_loop_body_in_dom_order, 
don't touch any visited flags.

Also, if you >  Aand this is by far the simplest way.  On contrary,
> I believe that the optimization passes should not use these flags.
> While inside the shared utility there is at least some justification for
> it (it saves you passing bitmap to it and other trouble), I see no
> justification why for example PRE cannot use sbitmap instead of touching
> BB_VISITED.
This just makes no sense to me, because you are saying we should do the 
same thing you don't want get_loop_body to have to do.