birthpoints in rtl.

[Diego Novillo]

On 2/28/08 8:03 AM, Kenneth Zadeck wrote:

> The big difference between what i am proposing with birthpoints and a
> full blown ssa implementation is that i plan to do no rewriting since
> there are no operands of the phis to support this.

You don't need to do a rewriting SSA implementation to have PHI nodes 
with operands.  FUD chains fully support PHI nodes with operands.


> I believe that what i am proposing is actually currently called (or at
> least related to) factored use def chains, but i need to read up on the
> literature to see if they really are the same.

Yes, they are.  FUD chains are what I initially used on GIMPLE, but they 
do not allow overlapping live ranges for different SSA names of the same 
symbol, so for GIMPLE registers I implemented the basic rewriting form 
and for memory symbols I implemented FUD chains (the SSA web over 
VDEF/VUSEs are FUD chains).

If we are not going to use a rewriting SSA form, I believe that the 
original problems we had with RTL-SSA can be avoided.


Diego.