[tree-ssa] CCP and non-destructive folding problems

[Diego Novillo]

On Tue, 2003-02-25 at 13:18, law@redhat.com wrote:

> We must be talking past each other.
> 
We?  Talking past each other?  ;)

Yes, now we are on the same page.  It's fine for evaluate_stmt() to
return VARYING when it can't fold for whatever reason.  If it couldn't
fold because of a limitation in the non-destructive folder then (a) it's
just a mis-optimization bug, and (b) we will likely fail in the final
replace and fold stage.

At that point we can decide whether to fix the non-destructive folder or
live with the mis-optimization.

> Now in the case where all the operands are constants, but we failed to
> fold the expression we have a "soft" failure if we return VARYING.  ie,
> we fail to optimize the code as much as we should.  Investigating to see
> how many of these are still lurking would be a good thing to do.
> 
Agreed.


Diego.