Re: [tree-ssa] Out of SSA status and issues

[Diego Novillo <dnovillo@redhat.com>]

On Tue, 2003-05-13 at 13:29, Jan Vroonhof wrote:

> However, Not treating this as a PRE problem might have the tendency to
> move the load towards entry and the store towards exit too much,
> increasing register pressure and putting loads and stores in codepaths
> that previously didn't have them. This seems to suggest leaving it to PRE.
> 
Exactly.  This is what we are converging to.  In my initial design, I
had thought that by treating INDIRECT_REF nodes like regular variables
would simplify the implementation and give us the extra benefit of being
able to do the same transformations we do to any other variable.  Boy,
was I wrong!

INDIRECT_REF nodes are like any other unary expression (OK, they have
slightly different semantics as they can be on the LHS of an
assignment), so the expression-SSA built by SSAPRE is perfect for them. 
All we need is to do is build the SSA form for expressions and let that
framework handle them.

Daniel, how clean is the separation between the expression-SSA and the
PRE specific bits in SSAPRE?  It'd be nice if we have a clean separation
between the infrastructure proper and the various passes we want to do
that operate on expressions.


Diego.