On Fri, Feb 29, 2008 at 20:39, Kenneth Zadeck <[EMAIL PROTECTED]> wrote:
> I personally dislike the fact that the middle end keeps the phi's separate. Six of one, half a dozen of the other. If you put the PHIs in the IL stream, then you need to be careful about not moving anything before or in between them. They also have different semantic properties: they execute all in parallel and so the result of one PHI cannot be used as an argument in another PHI in the same block. Things like SSA propagation need to treat them differently, etc. Some things would potentially become easier, while others become more difficult. It would probably a good experiment to run on a branch some time. > Then my plan is to "adapt" as much of the tree ssa code (there is no > reason for me to write dominance frontier code for the 4 time from > scratch) You don't need to. Dominance information is completely IL independent. It only needs the CFG. > [ ... ] and can just adapt the ssa stack based renaming algorithm to build > the chains rather than rename the vars. I have no idea if wolfe ever > figured this part out or not. Yes, he did. That's the main point behind my proposal. Both FUD chains and rewriting SSA operate in *exactly* the same way, we do not need two renaming algorithms in tree-into-ssa.c. The only difference between FUD chains and rewriting SSA is that the former does not modify the statement, it merely rewrites the VDEF/VUSE operands (thus creating the SSA web). If you adapt the algorithm to simply rewrite the DF chains, you will be set. FUD chains are never part of the IL, so by converting the UD links to factored UD links in the DF data structure, you should be able to get all the benefit of the sparser representation. What if you treated subregs as total writes (like we do arrays) and libcalls as clobbering points? Though I guess that may not be sufficient. Diego.
