Chandler Carruth 8c0b41d656 Add a somewhat hacky heuristic to do something different from whole-loop ...

rotation. When there is a loop backedge which is an unconditional
branch, we will end up with a branch somewhere no matter what. Try
placing this backedge in a fallthrough position above the loop header as
that will definitely remove at least one branch from the loop iteration,
where whole loop rotation may not.

I haven't seen any benchmarks where this is important but loop-blocks.ll
tests for it, and so this will be covered when I flip the default.

llvm-svn: 154812

2012-04-16 13:33:36 +00:00

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