[tree-ssa] Maintaining/representing def-use/use-def information

[Andrew MacLeod]

On Mon, 2003-12-15 at 15:55, Zdenek Dvorak wrote:
> Hello,
> 
> > Ultimately, I dont see much difference other than implementation
> > details...
> 
> ... and about three times more memory spent, I would estimate. For a
> single assignment statement, we have:

Which is an implementation detail, not an architecture one.
> 
> 1) The var_decl node
> 2) The ssa name
> 3) modify_expr
> 4) operation_expr
> 
> + pointers to link them together, versus
> 
> 1) single entity containing just the operation code and two pointers to
>    the arguments (+additional information like type, etc).
> 

Yes, but that is not what we were discussing, we were discussing that
ssa-names were not first class citizens nor well integrated into the
compiler.

Absolutely we spend more memory in tree form, I never claimed that we
didn't. And there are plans to do something about that.  Both compressed
trees and compressed rtl have both been proposed, but no one has
bothered with it yet. I would expect that it would have very similar
memory properties once its done. Its simply not an SSA specific problem,
but rather an overlal tree issue.

Andrew