Fix LoopUnswitch bug. RewriteLoopBodyWithConditionConstant can delete a dead case of a switch instruction. Back off this optimization when this would eliminate all of the predecessors to the latch.
Fix LoopUnswitch bug. RewriteLoopBodyWithConditionConstant can delete a dead
case of a switch instruction. Back off this optimization when this would
eliminate all of the predecessors to the latch.

Sorry, I am unable to reduce a reasonably sized test case.

rdar://9486843


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@132022 91177308-0d34-0410-b5e6-96231b3b80d8

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