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cold loops as-if they were being optimized for size. Nothing fancy here. Simply test case included. The nice thing is that we can now incrementally build on top of this to drive other heuristics. All of the infrastructure work is done to get the profile information into this layer. The remaining work necessary to make this a fully general purpose loop unroller for very hot loops is to make it a fully general purpose loop unroller. Things I know of but am not going to have time to benchmark and fix in the immediate future: 1) Don't disable the entire pass when the target is lacking vector registers. This really doesn't make any sense any more. 2) Teach the unroller at least and the vectorizer potentially to handle non-if-converted loops. This is trivial for the unroller but hard for the vectorizer. 3) Compute the relative hotness of the loop and thread that down to the various places that make cost tradeoffs (very likely only the unroller makes sense here, and then only when dealing with loops that are small enough for unrolling to not completely blow out the LSD). I'm still dubious how useful hotness information will be. So far, my experiments show that if we can get the correct logic for determining when unrolling actually helps performance, the code size impact is completely unimportant and we can unroll in all cases. But at least we'll no longer burn code size on cold code. One somewhat unrelated idea that I've had forever but not had time to implement: mark all functions which are only reachable via the global constructors rigging in the module as optsize. This would also decrease the impact of any more aggressive heuristics here on code size. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200219 91177308-0d34-0410-b5e6-96231b3b80d8
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