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Re: [tree-ssa] Removal of gotos from cfg based ir


In message <1068840451.2358.262.camel@p4>, Andrew MacLeod writes:
 >Yes, no one is arguing that we dont need a cfg, you build that as an
 >encapulation/summary of flow through the IL. The disagreement is whether
 >the cfg ought to be an integral part of the IL description or not. Like
 >every other data structure that the optimizers use, I think it ought to
 >be referred to for information, not used to drive the IL.
Precisely. 


 >If the original intention was to do this, we didn't even need to lower
 >the original container stmts, you just detach them when we build the
 >CFG, and let the CFG decide where everything is, and then reattach
 >things to the appropriate container when we destroy the CFG. That would
 >have been a much simpler way of getting there than going through all the
 >pain of lowering the stmt chain into a single list, then breaking it up.
 >It would have been much easier to convince me of this before we went to
 >all the effort of lowering the code. Some of us even discussed the
 >possibility of integrating the CFG a year ago when it was containers,
 >but lots of other changes were happening at the time. Now that its
 >lowered, I see even fewer reasons to do it.
Based on my experience with our nested IL, I would tend to strongly 
disagree.  While it may seem like we could use the CFG and the old
containers to do this, I don't think it would have worked.

This was made painfully clear to me with the problems created when we
started threading jumps -- it tends to leave us with highly unstructured
code.  Or imagine the problems with BIND_EXPRs -- to make this scheme work
we would have had to had more magic for BIND_EXPRs, or we would have needed
to treat them as starting/ending basic blocks.

The lowering of the IL was a good thing, regardless of whether or not
Zdenek had other long term goals.


Jeff



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