[PATCH] Add a flag to experiment with outlining optional branches.

[hfinkel at anl.gov]

In http://reviews.llvm.org/D7719#125705, @djasper wrote:

> As previously discussed on IRC, using the post dominator tree is probably not an option for performance reasons.


I highly recommend measuring the performance of the post-dom-tree version before concluding it is too expensive. True, we've traditionally avoided them. But we also added use of a post-dom tree to the MachineSink pass, because it was the right way to solve the problem, and the compile time cost increase turned out to be relatively small.

> I'll try to come up with an implementation that doesn't need it. If we had it, the implementation can actually be simplified as in this version of the patch (a single lookup in the dominator tree instead of many). Just adding this for documentation of the progress.





http://reviews.llvm.org/D7719

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