birthpoints in rtl.

[Diego Novillo]

On 2/27/08 6:15 PM, Kenneth Zadeck wrote:

> Comments? Volunteers?

How about adding FUD chains instead of the dense UD chains we have 
today?  FUD chains are almost trivial to port from gimple-ssa into RTL. 
We already overlay a use-def web on the RTL representation using the new 
dataflow bits.

Unless I'm missing something obvious, we could easily convert those 
dense chains into factored chains by inserting real PHI nodes and 
building a FUD chain web.

The code to compute insertion points is almost totally independent from 
the IL (it should not be hard to adapt to the DF def/use 
representation).  We just need to have a way of representing PHI nodes. 
  No changes to the RTL representation should be necessary.

We could even adapt the global live-in computation to prune the 
dominance frontiers.  But that's just an optimization.

I may be able to spend some time on this.



Diego.