PRE in gcse.c

[Alexander Larsson <alla at lysator dot liu dot se>]

I'm currently as part of my masters thesis implementing partial redundancy 
elimination. I use a Lazy Code Motion approach described in Knoop, Ruthing and 
Steffen, "Optimal Code Motion: Theory & Practice" ACM Trans. on Programming 
Languages and Systems 16(4):1117-1155, July 1994. Available at
http://sunshine.cs.uni-dortmund.de/~ruething/ocm.ps.gz

Out of interest i checked out what kind of gcse egcs used and saw that it uses 
an older version of partial redundancy elimination described by Morel and 
Renvoise. I am not very familiar with the gcc source, and i haven't looked 
very deeply at this, but would there be any interest in an LCM version of 
gcse.c? This has two advantages, first register life-times are minimized and 
second the data-flow analysis is (supposedly) simpler and faster.

In the source i did find a comment that said:
 Eventually it would be nice to replace cse.c/gcse.c with SSA (static single
 assignment) based GVN (global value numbering).  L. T. Simpson's paper
 (Rice University) on value numbering is a useful reference for this.

Is anybody working on this? I think i saw some reference to phi in a mail some 
time ago.
 
/ Alex