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[PM] Port LoopSink to the new pass manager.

Description

[PM] Port LoopSink to the new pass manager.

Like several other loop passes (the vectorizer, etc) this pass doesn't
really fit the model of a loop pass. The critical distinction is that it
isn't intended to be pipelined together with other loop passes. I plan
to add some documentation to the loop pass manager to make this more
clear on that side.

LoopSink is also different because it doesn't really need a lot of the
infrastructure of our loop passes. For example, if there aren't loop
invariant instructions causing a preheader to exist, there is no need to
form a preheader. It also doesn't need LCSSA because this pass is
only involved in sinking invariant instructions from a preheader into
the loop, not reasoning about live-outs.

This allows some nice simplifications to the pass in the new PM where we
can directly walk the loops once without restructuring them.

Differential Revision: https://reviews.llvm.org/D28921

Details

Committed
chandlercJan 20 2017, 12:42 AM
Differential Revision
D28921: [PM] Port LoopSink to the new pass manager.
Parents
rL292588: [LoopSink] Trivial comment cleanup.
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