On Dec 10, 2007 11:36 AM, Evan Cheng <[EMAIL PROTECTED]> wrote: > On Dec 10, 2007, at 6:47 AM, Dan Gohman wrote: > > And if that's all it's doing, MachineLICM's traversal could be > > simplified > > a little. Instead of visiting each loop individually, taking care to > > avoid > > revisiting to blocks within inner loops, the pass could just traverse > > entire outer-most loops, which will implicitly include the blocks of > > any > > inner loops. Instructions nested deep in inner loops can then be > > hoisted > > all the way out of the outer-most loop in a single step instead of > > being > > hoisted out one loop at a time. > > I don't think lifting loop invariant from inner loop all the way out > of outer-most loop is a good idea. That will increase register > pressure in basic blocks where it is not used. > This is going to happen with the current pass, though. Each loop is going to see the hoisted instructions from the previous iteration and try to re-hoist them. Is there some heuristic we should apply to prevent it from hoisting instructions too far?
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