Re: Replace rename_ssa_into_ssa with update_ssa

[Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>]

Hello,

> This patch brings over most of the changes in tree-cleanup-branch.  
> I think that all that's left is the re-ordering of tree passes.
> 
> The main change in this patch is the replacement of rewrite_ssa_into_ssa
> with update_ssa (the incremental SSA updating mechanism).  As a
> side-effect of this change, it is no longer necessary to keep
> virtual operands in loop-closed SSA form.  This provides some
> nice compile time speedups in the loop passes.

hmm... I wonder whether this is really a good idea.  This means that
operations like loop unrolling will leave the ssa form for virtual
operands broken, making it impossible to use it until update_ssa is
called.  How much do we really gain by it?  I.e. do you have some
comparison between the compile time difference between your patch, and
your patch that leaves the virtual operands in loop closed ssa form?

If I understand your patch correctly, you have
removed the specialized versions of ssa form updating from
tree_duplicate_loop_to_header_edge and tree_duplicate_sese_region.
Why?  They should be more efficient than calling the generic updating.

Could you please remove my name from the changelog entry?  I have
nothing to do with this patch (even if you were inspired by some of my
patches, it was very, very losely and somewhat in contradiction of my
ideas).

Zdenek