Re: [RFC] [autovect patch] Implement vectorization hints

[Devang Patel <dpatel at apple dot com>]

On Mar 2, 2005, at 11:38 AM, Zdenek Dvorak wrote:

> Hello,
> > > > Just FYI, xlc associates the info with the loop in a loop table (the
> > > > frontend creates the initial loop table), and keeps the loop table 
> > > > up
> > > > to
> > > > date forever onwards :)
> > > But GCC does not keep up to date loop tables ;).
> > This won't change if everyone just keeps on doing other things instead
> > of doing the work necessary to start this.
> I will start working on that; as a first step, I will try to get
> loop-aware cfg cleanup merged, rest of the tree loop optimization 
> passes
> should not be too problematic hopefully.

With your patch to make cfg cleanup loop aware,
    http://gcc.gnu.org/ml/gcc-patches/2005-03/msg00244.html

I tried to initialize loop structure as early as possible, so I put it
immediately after build_ssa. Jump threading immediately ran into 
problems
when loop header block is threaded. For example,

                     + ----> [3] ---> Exit
                     |
Entry ---> [0] ---> [2] <---+
                     |      |
                     v      |
                    [1] ----+

Here [2] is loop header and [1] is loop latch.

After jump threading

Entry ---> [0] ---> [4] ---> [1] <---+
                              |      |
                              v      |
                             [2] ----+
                              |
                              + ----> [3] ---> Exit


This means thread_blocks() need to update loop structure in this
case. But resulting cfg does not match loop criteria. latch does
not have exactly one successor.

Any thoughts how to handle this?

Thanks,
-
Devang