[ast-optimizer-branch] Simplification of Simple grammar

[Sebastian Pop]

On Wed, Mar 27, 2002 at 09:11:35AM -0500, Diego Novillo wrote:
> On Wed, 2002-03-27 at 08:38, Sebastian Pop wrote:
> 
> > I think that the scope of Simple is to simplify the analysis and transformations
> > we will write on Simple.  Since we don't lose information by transforming
> > all switches in nested IF_STMTs, or transforming all loop structures 
> > into DO_STMTs, I propose to simplify Simple grammar a little. 
> > 
> Actually, we lose valuable information if we simplify the grammar any
> further.  The main example that comes to mind are FOR loops.  Once you
> convert them to an IF/DO_WHILE combination, you lost the original
> semantics and things get ugly for things like loop parallelization.
> 
Agree. 
I will keep the transformations for the 3 loop structures as already 
implemented for the goto/break elimination.  In this case I will only need
the switch elimination to be applied before eliminating GOTO_STMTs. 

> My suggestion is that for GOTO elimination, you create another pass to
> further simplify the control structure into low-SIMPLE.  I would rather
> do things in phases.  Some analyses and/or transformations might be
> better done in high-SIMPLE.
> 
> After all, the grammar for low-SIMPLE that you're proposing is a strict
> subset of high-SIMPLE.  The RTL conversion does not need to change. 
> Furthermore, doing this in phases will give us better control when we
> start testing transformations.  We have to watch out for code bloat and
> increased compilation times.  It's easier to calibrate things when
> dealing with lego-like modules instead of one monstruous black-box.
> 

Right.

What about modules like :
- switch_to_if
- for_to_do
- while_to_do

These functions can be called separately on passes that need a special form 
of the Simple grammar.


Seb.