Re: [tree-ssa] where to fix this?

[Daniel Berlin <dberlin at dberlin dot org>]

On Jan 6, 2004, at 7:29 PM, law@redhat.com wrote:

> In message <FFCAFC47-40A3-11D8-8CD1-000A95DA505C@dberlin.org>, Daniel 
> Berlin wr
> ites:
> > > When we follow def-use chains in the dominator optimizer to 
> > > reassociate
> > > and simplify operands.  The stuff we do right now is pretty simple, 
> > > but
> > > it's one of the two areas of the dominator optimizer that I do expect
> > > will need to be extended.
> >
> > I tried a variant on this back right before we had renaming SSA.
> > It was a forward and backward substitution pass, which tried to see if
> > any of the resulting expressions were GIMPLE (after trying folding, of
> > course).
> > They never were.
> Apparently your code was buggy or you weren't looking at the right 
> stuff.
That's a bit harsh of a statement (not that i'm surprised, however).

However, I was mainly interested in substitution of array indexing 
expressions, for the purposes of simplifying array access expressions.

> I've definitely got cases where were substitution & folding results in
> a gimple expression.

Wake me when you've got percentage speed increase or decreased memory 
usage (due to less expressions) numbers.

Simply the number of expressions eliminated means nothing really by 
itself.

--Dan