[llvm] [VPlan] Supported conditionally executed single early exits. (PR #182395)

[Luke Lau via llvm-commits]

https://github.com/lukel97 commented:

I think this approach is fine, but it's a shame we have to leak information about the current block mask through MaskedCond. 

I think it's possible to handle this all within the CFG if we branch to the latch on the exiting condition, and insert a phi in the latch with false as the incoming value on the non-earlyexiting block. The predicator will generate a `select earlyexiting-blockmask, earlyexit-cond, false` which is the same logical and. 

But maybe we can look at doing that closer to #172454

https://github.com/llvm/llvm-project/pull/182395