Guys,Yes, I am interesting in this. Could you give me the reference to WCP details (I can not find the document on the Internet). I could give it a try. May be this approach will work.
I have done some experiments on two different heuristics for superblock scheduling by comparing them with optimal scheduling. The two heuristics are simple critical path CP (priority is the CP from the last branch only) and weighted critical path WCP (priority is a weighted sum of critical pahts from all branches below an instruction, with the branch weight being the probability of exiting the superblock at that branch). On the simple machine model that I am using, I got the following results:
fp2000 benchmark: CP is optimal on 72% of the superblocks and WCP is optimal on 84% of the superblocks
int2000 benchmark: CP is optimal on 83% of the superblocks and WCP is optimal on 94% of the superblocks
These numbers do not necessarily reflect actual run-time performance improvements, since they were collected in a standalone setup were superblock data dependence graphs were extracted from gcc and scheduled
separately for a simple machine model (dual issue in which one int and one fp instruction can issue in each cycle). However, these results do suggest that the WCP heuristic is significantly better than the simple CP.
The reference for the WCP heuristic is:
R. Bringmann, Compiler-Controlled Speculation, PHD thesis, Dept. of CS, UIUC, IL 1995. (where the technique is called Dependence Height and Speculative Yield DHASY).
However, you don't really need to go there since the heuristic itself is so simple and intuitive that my description above is almost sufficient. Let me know if you are interested and I'll give you the details and explain one particular subtility about it.
Vlad
