Scalar Replacement

Scalar Replacement

[Canqun Yang]

Hi, all

I'm going to implement scalar replacement optimization 
on trees of GCC backend. Does anyone plan to do the 
same work? If so, please let me know.

By now, the problem I encountered is the 
representation for array references of Fortran 95. As 
Gnu Fortran 95 frontend converts multi-dimensions 
arrays to one-dimension array references, it is hard 
to recover the number of dimensions and the index of 
each dimension for array references. This makes the 
dependence relation analysis failed to perform on tree 
loops.

Is there any way to recover those information without 
modifying the Fortran 95 frontend?

Or, if not. How to modify the frontend to satisify 
this? 

I'm looking forward for suggestions. 



Canqun Yang
Creative Compiler Research Group.
National University of Defense Technology, P. R. China.

Re: Scalar Replacement

[Steven Bosscher]

On Sep 22, 2004 05:03 PM, Canqun Yang <canqun@nudt.edu.cn> wrote:

> I'm going to implement scalar replacement optimization 
> on trees of GCC backend.

See tree-sra.c.
Gr.
Steven

Re: Fortran array format [Was: Scalar Replacement]

[Paul Brook]

On Wednesday 22 September 2004 16:03, Canqun Yang wrote:
> By now, the problem I encountered is the
> representation for array references of Fortran 95. As
> Gnu Fortran 95 frontend converts multi-dimensions
> arrays to one-dimension array references, it is hard
> to recover the number of dimensions and the index of
> each dimension for array references. This makes the
> dependence relation analysis failed to perform on tree
> loops.
>
> Is there any way to recover those information without
> modifying the Fortran 95 frontend?

This sounds like what the linear loop transform and scalar evolutions stuff is 
doing.

> Or, if not. How to modify the frontend to satisify
> this?

The fortran frontend should be changed to use the [relatively] new 
multiple-argument form of ARRAY_REF.

However before that happens we should check with the tree-ssa and loop 
optimization people that the current ARRAY_REF format does provide the 
necessary information in an efficient and convenient form.

This was discussed a bit at the last GCC summit, although I don't think we 
reached any conclusions. Basically it would be nice to have some way of 
communicating fortran array structure to the optimizers. However I don't 
think anyone's figured out how best to do this, or how it would fit in with 
out existing optimization framework.

Paul